BACKGROUND

[0001] Few people appreciate the important roles compressors play in everyday life much less how important they are in many industries. Refrigerators, air conditioning systems, pneumatic power systems, and a vast array of industrial, commercial and other systems all rely on compressors. Moreover, vacuum pumps also underlie a number of industries. For instance, many processes in the semiconductor industry require the evacuation of air from fabrication chambers which in essence require rarified air in the fabrication chambers to be "compressed" and discharged to the atmosphere (or elsewhere). Bulk chemical processes, of course, also rely on compressors. For instance, the production, storage, and transportation of gaseous hydrocarbon fuels require that literally millions of cubic meters of gas be compressed (and often to or beyond the point of liquefaction).

[0002] Compressors, though, consume relatively large amounts of power, require relatively large amounts of cooling, are often bulky, and tend to breakdown more often than would otherwise be desired. The power needs arise from the energy intensive physics of compressing gases and, of course, these needs escalate as the desired compression ratio rises. Moreover, compressing gases causes a largely adiabatic temperature increase which makes compressing the gases just that much more energy-intensive. The gases also often impart the associated heat to the compressor itself thereby leading to the need to use specialty high-temperature materials, heat-related corrosion issues, heat-related failures, etc.

[0003] Common rotary compressors moreover, require special bearings to absorb the loads imparted by the rotating driver, motor, or other power source. They also tend to be capacity-limited because of the large centripetal forces developed by the drivers. These forces also complicate the design of the drive shafts, their bearings, and related seals of heretofore available compressors. Because of the rotational inertia of the drivers, moreover, such compressors tend to be limited in their ability to respond rapidly to load changes. SUMMARY

[0001] The following presents a simplified summary in order to provide a basic understanding of some aspects of the disclosed subject matter. This summary is not an extensive overview of the disclosed subject matter, and is not intended to identify key/critical elements or to delineate the scope of such subject matter. A purpose of the summary is to present some concepts in a simplified form as a prelude to the more detailed disclosure that is provided herein. The current disclosure provides systems, apparatus, methods, etc. for compressing gases and more specifically for compressing hydrocarbon-related gases in reliable and efficient manners.

[0002] Compressors find use in a large variety of contexts in which the pressure and/or density of a gas needs to be increased. For instance, in the petro-chemical industries it is often desired to liquefy natural gas for storage and/or shipment and without substantial impurities such as other gases, water, etc. In perhaps a more mundane context, large quantities of natural gas and/or petroleum gas (that is various mixtures of largely methane, ethane, propane, butane, etc.) are compressed for use in barbeque pits, for fueling vehicles, powering generators, driving large scale energy production, etc. Of course, various gases can also be compressed to increase their reaction rate in a variety of industrial applications too numerous to enumerate practicably. Typical cooling systems (for instance, refrigerators, air conditioners, and the like) likewise require compressors to pressurize cooling fluids like Freon® in order to enable the cooling/expansion cycle. Of course, other gases need to be compressed for a wide variety of purposes such as oxygen for medical purposes, hydrogen for use as a fuel, etc.

[0003] Yet most if not all compression processes generate large quantities of heat due to the nearly adiabatic compression of the gases involved. While low-boiling temperature fluids can be used as coolants in a small fraction of these applications, other more heat-intensive applications require the use of potentially environmentally- unfriendly, higher-temperature and/or more efficient coolants. And, of course, compression efficiency decreases as the discharge temperature of the compressed gas increases. Thus, attaining lower discharge temperatures is often desirable and can be done without excessive water use and or without the use of toxic or environmentally detrimental coolants in accordance with embodiments. [0004] Compressors of embodiments can be easily integrated with one another because the discharge strokes of the (relatively) low pressure stages and (relatively) high pressure stages are synchronized. Compressors of these embodiments do not require intermediate receivers to hold the gases compressed in upstream stages while the downstream stages ready themselves to accept those gases. Moreover, because of such internal/inherent synchronization, several such compressors can be interconnected to achieve relatively high compression ratios. And, as further disclosed herein, the series of compressors can be synchronized by coordinating the strokes of their drive shafts in relatively simple control schemes.

[0005] Moreover, compressors of various embodiments are relatively easy to service and repair thereby enabling simplified and less expensive maintenance. Such compressors also tend to be easier and less expensive to manufacture while being compact enough for use in both stationary and mobile applications. Moreover, compressors of the current embodiment experience lower dynamic loading which leads to increased reliability as compared to heretofore available compressors.

[0006] Gas compressor systems of embodiments comprise at least two multistage compressors with their low-pressure and high-pressure zones connected with gas pipes. The high-pressure zone or stage has at least one piston compressor and the low- pressure zones also have at least one low-pressure compressor. One feature of these multistage compressor systems is that the hydraulic drive(s) are connected by the same rod (or drive shaft) to the piston compressors of the low and high-pressure zones. The gas inlet of the high-pressure compressors are connected with the outlets of the low-pressure compressors. The control of the reciprocating motion of the hydraulic drives is carried out with the help of limit switches or other types of position sensors (for instance, continuous analog position sensors) in communication with a controller.

[0007] In such compressor systems, the working hydraulic fluid is supplied to all the hydraulic drive cylinders simultaneously and the movement of their pistons is controlled by the limit switches. To synchronize the operations of the compression stages, the limit switches develop a common signal that, when the signals are present in all the sensors (at a particular end of the stroke and/or a particular position of the pistons), the signal indicates that all compressor stages have reached a common position in their respective strokes. Thus, the control scheme of the current embodiment synchronizes the strokes of all of the stages. Moreover, the limit switches of the current embodiment can be non-contact, magnetically operated, sealed switches, inductive sensors, sonar-based sensors, radar-based sensors, etc.

[0008] Compressors of various embodiments possess relatively high degrees of integration in that they comprise various numbers of similar compressor modules.

These compressor modules are connected with pipes, tubes, manifolds, etc. so that the various compression stages are in fluid communication with one another such that the low pressure stages feed the high pressure stages with all of the stages being synchronized in operation.

[0009] This synchronization ensures that the low pressure stages feed the high pressure stages as the high pressure stages are attempting to draw fluid into themselves. And, because the high pressure stages are drawing gas at the same time that the low pressure stages are discharging gas, these systems require no intermediate reservoirs, tanks, pressure vessels, etc. to temporarily store gas surges from the low pressure stages. Nor do the high pressure stages risk being starved for gas as they move through their intake strokes. Thus, compression systems of the current embodiment tend to be simpler, less expensive to operate, and more reliable and efficient.

[0010] Moreover, because only one assembly (the shaft assembly) moves, compressors of many embodiments are easier to service, easier to repair, and simplify maintenance thereby reducing operating expenses. Compressor systems of embodiments are also less expensive to design and/or manufacture since their design is largely based on the number of modules desired, the compression ratios across the various stages (as determined by their relative displacement volumes), their interconnections, and the common stroke length of the various compression modules.

In some embodiments, two or more compressor modules are placed in line and driven by a common drive shaft. These multi-module systems can be oriented in just about any orientation from horizontal to vertical and/or in between. Note that the use of a common drive shaft (if desired) synchronizes all of the compression stages driven by that shaft.

[0011] Some embodiments provide pumps comprising pistons, first stage cylinders, shafts and second stage cylinders. In such embodiments, one side of the piston can be said to be hollowed thereby forming a coolant chamber and heat fins. These pistons define shaft and coolant sides and slidably engage the first stage cylinders. Furthermore, the first stage cylinders at least partially extend beyond the coolant sides of the pistons. The shafts operatively couple to the shaft sides of the pistons and extend into the first stage cylinders. The second stage cylinders operatively couple to the coolant sides of the pistons and extend into the first stage cylinders.

[0012] Note, that herein the term "pump" will be used to refer to various embodiments because depending on the interconnections between stages (and/or lack thereof) the disclosed embodiments can act as either pumps (when handling liquids) and/or compressors (when handling both). And, furthermore, because two phase conditions might exist in the pumps, compressors, modules, systems, etc. disclosed herein the term "pump" will be used. On that note, moreover, because embodiments use positive displacement pistons, little or no cavity is expected during the operation of the pumps even with two phase conditions occurring. This is in contrast to what might be expected with rotary bladed pumps and/or compressors. These two phase capabilities also contribute to the ease of maintenance and reliability of pumps of various embodiments.

[0013] Note also that the second stage cylinders can be configured as heat fins in having relatively thin thicknesses and being made of materials with relatively high thermal conductivity. As desired, some pumps can further comprise alignment shoes positioned in the cylinders so as to align the heat fins (second stage cylinders) with the pistons and first stage cylinders. These alignment shoes can be coupled to the heat fin. Note that the heat fins and cylinders are concentric and spaced apart from one another in some embodiments. In addition, or in the alternative, in some pumps, the first stage cylinders extend beyond the shaft sides of the pistons thereby defining displacement volumes. In some of these pumps, the shafts have outer diameters approximately equal to the inner diameters of the displacement volumes and formed so called "plunger" stages wherein the shaft acts as a piston rather than relying on a separate piston. Of course, the pumps can comprise working fluid chambers and working fluid pistons which are coupled to the shaft so that a working fluid drives the shafts.

[0014] In some embodiments, the pumps further comprise seals carried by the shafts located in the displacement volumes and/or the first stage cylinders define cooling fluid ports in fluid communication with the heat fins. If desired, the heat fins and the cylinders define additional, second stage, displacement volumes. And when these pumps also include alignment shoes, these shoes can seal the additional, second stage displacement volumes. Various embodiments also comprise seals positioned between the heat fins and the first stage cylinders.

[0015] Additionally, other embodiments provide pumps comprising shafts, pistons coupled to the shafts, and cylinders. The cylinders define piston-associated displacement volumes and shaft-associated displacement volumes. In such pumps, as the shafts reciprocate, the pistons pump fluid in the piston-associated displacement volumes and the shafts pump fluid in the shaft-associated displacement volumes. Note also that in pumps of these embodiments the shafts haves outer diameters about equal to the inside diameters of the cylinders in the piston-associated displacement volumes. Additionally, the shafts of these embodiments have outer diameters about equal to the inner diameters of the cylinders in the shaft-associated displacement volumes whereby the shaft can be said to define a "plunger" stage.

[0016] In addition or in the alternative, pumps of embodiments further comprise seals coupled to the shafts in the shaft-associated displacement volumes. Moreover, some pumps further comprise additional pistons which, in conjunction with the cylinders, define additional displacement volumes associated with the additional pistons. Cylinders of various embodiments further define additional shaft-associated displacement volumes. Pumps, of some embodiments, further comprise additional pistons which, in conjunction with the cylinders define additional displacement volumes wherein the cylinders define additional shaft-associated displacement volumes.

[0017] To the accomplishment of the foregoing and related ends, certain illustrative aspects are disclosed herein in connection with the annexed figures. These aspects are indicative of various non-limiting ways in which the disclosed subject matter may be practiced, all of which are intended to be within the scope of the disclosed subject matter. Other advantages and novel features will become apparent from the following detailed disclosure when considered in conjunction with the figures and are also within the scope of the disclosure.

BRIEF DESCRIPTION OF THE FIGURES [0018] The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number usually identifies the figure in which the reference number first appears. The use of the same reference numbers in different figures indicates similar or identical items.

[0019] Fig. 1 illustrates a variety of scenarios involving compressed gases.

[0020] Fig. 2 illustrates a cross-sectional view of a pair of gas compressor modules.

[0021] Fig. 3 illustrates a plan view of a gas compressor.

[0022] Fig. 4 illustrates a plan view of another gas compressor.

[0023] Fig. 5 illustrates a plan view of a gas compressor with inter-stage cooling features.

[0024] Fig. 6 illustrates a top plan view of a compressor in a cooling tank.

[0025] Fig. 7 illustrates a control system for a pair of compressors.

[0026] Fig. 8 illustrates a compressor with concentrically arranged compression stages.

[0027] Fig. 9. Illustrates a flowchart of a method in accordance with embodiments.

[0028] Fig. 10 illustrates a block diagram of a controller for one or more compressors.

[0029] Fig. 11 illustrates a multi-stage pump of embodiments.

[0030] Fig. 12 illustrates another multi-stage pump of embodiments.

[0031] Fig. 13 illustrates yet another multi-stage pump of embodiments.

DETAILED DESCRIPTION

[0032] This document discloses systems, apparatus, methods, etc. for compressing gases and more specifically for compressing hydrocarbon-related gases in reliable and efficient manners.

[0033] Fig. 1 illustrates a variety of scenarios involving compressed gases. More specifically, Fig. 1 illustrates an LNG (Liquefied Natural Gas) "super-tanker," 102, an industrial-sized natural gas tank 104, and a residential-style propane tank 106. The LNG super-tanker 102 includes several insulated tanks 108 which, cumulatively, can hold several hundred thousand cubic meters of LNG. Of course, to liquefy the natural gas, compressors are often employed to raise their pressure in conjunction with heat exchangers and/or other equipment to produce a relatively dense liquid in a form more suitable for transportation, distribution, use, etc. While Fig. 1 illustrates only 1 LNG super-tanker 102, it is noted here that dozens (if not hundreds) of LNG super - tankers sail the oceans, rivers, and other waters of the Earth transporting LNG to many locations around the world. In addition to the number of LNG super-tankers 102 that exist, the presence of extensive LNG (and other hydrocarbon) pipelines/networks in most industrialized countries shows how large the market is for such compressed gases/liquids.

[0034] Fig. 1 also illustrates that many factories, chemical plants, municipalities, need to store gaseous fuels in bulk. Moreover, at many remote locations, users desire to store compressed natural gas for a variety of uses. For instance, many farms, ranches, households, etc. include a natural gas tank 104 (but of smaller size) from which they draw natural gas for heating and/or other purposes. Furthermore, the propane tanks

106 illustrated by Fig. 1 find use in a variety of places such as residential barbeque pits, fuel tanks for golf/utility carts, fuel tanks for emergency electricity generators, etc. And, again, while they are small individually, these propane tanks 106 represent a large cumulative market. Thus, Fig. 1 illustrates a few of the large number of demands for compressed gases.

[0035] Fig. 2 illustrates a cross-sectional view of a pair of gas compressors. Of course, as disclosed elsewhere herein, compressors are used to compress the gases involved in the applications illustrated by Fig. 1 as well as many other applications. Provided herein are compressors, methods of compressing gases, and associated apparatus, systems, and methods including the compressors illustrated by Fig. 2. The compressor system 200 of the current embodiment can compress a wide variety of gases to high compression ratios efficiently and reliably.

[0036] The compressor systems 200 of embodiments, includes a pair of compressors 202 and 204 each having pairs of low and high pressure stages (4 stages per compressor, 8 stages in the system) with double acting pistons and possibly differing displacement volumes in each stage. For instance, the displacement volumes in successive stages can decrease such that compression is achieved across each stage (and/or various combinations of stages). Of course other numbers of compressor modules, stages, etc. are within the scope of the current disclosure. And in at least one sense of the term "stage," each side of each double acting piston can define a

"stage." Moreover, each compressor 202 and 204 comprises one double acting hydraulic/pneumatic drive piston situated between the pairs of low/high pressure stages. Each low pressure stage feeds the corresponding high pressure stage and the double acting pistons of each pair of stages acts in the same direction due to the common drive shaft for all of the pistons/stages of a given compressor.

[0037] However, because the drive pistons are situated between the pairs of low/high pressure stages, one pair of stages is acting in one direction (for instance, compressing the gas therein on one side of the respective pistons) while the other pair of stages (on the opposite side of the drive piston) is operating (compressing) in the other direction. Still with reference to Fig. 2, the drawing shows that between the two compressors 202 and 204, the compressor system 200 includes 8 stages (stages I to VIII) of compression. Stages I, III, V, and VII have relatively large displacement volumes (and/or diameters) while stages II, IV, VI, and VIII have smaller displacement volumes (and/or diameters). Moreover, I, III, V, and VII feed stages II, IV, VI, and VIII respectively. And stages II and VI of compressor 202 also feed, respectively, stages III and stage VII of compressor 204. In other words, the first compressor 202 feeds the second compressor 204. Note that stages I and V draws gas from the inlet of the compressor system 200 while stages IV and VIII discharge compressed gas to the outlet of the system. And, in the current embodiment, each of the compressors 202 and 204 have drive shafts with the same stroke (and are driven in parallel) so that all compressor stages I to VIII share that stroke length also and operate in synchronization. In some embodiments, though, various modules can have differing strokes provided that the velocities of the various shafts are coordinated to provide synchronized operation and or surge tanks or the like are employed to facilitate operations of such systems.

[0038] In operation, therefore, as stage I draws gas from the inlet on one side of its double acting piston, the other side of the stage I double acting piston feeds one side of the double acting piston of stage II. The other side of the stage II double acting piston meanwhile drives gas to stage III. Stages III and IV, stages V and VI, and Stages VII and VIII act in a similar manner (when the drive rods move in direction A). When the drive rods move in direction B (as indicated by another arrow), the process repeats but with the opposite sides of the double acting pistons driving the gas (and/or drawing gas from their inlets). And, because, the even numbered stages have smaller displacement volumes (with the same stroke), relatively low pressure gas is compressed in the odd-numbered stages as it is driven into the even-numbered stages. The gas is further compressed as it is driven from the even number stages to the odd numbered stage (in the next pair of stages).

[0039] This arrangement also results in a relatively steady flow of gas from the system overall. More specifically, because both of the pairs of stages of a pump are always (acting in one direction or another) compressing (and discharging) gas, it is anticipated that the compressors of the current embodiment will produce approximately ½ of the flow/pressure pulsations that other positive displacement compressors produce. And, of course, since in the current embodiment, the drive piston acts in a linear manner, the compressors experience none of the centripetal forces generated by a revolving drive shaft (and their prime drivers). Moreover, because the drive shafts need not overcome its compressors' rotational inertia, the compressors of the current embodiment can respond to load changes relatively quickly.

[0040] Further still, Fig. 2 illustrates that for the two compressors shown, their (two pairs of) four stages of compression are arranged in series leading to a relatively large potential compression ratio. And this result is true no matter which direction the drive shafts are moving. More specifically, when gas flows into the low pressure stage I of the upstream compressor 202, it is compressed and flows to the high pressure stage II of that upstream compressor 202. In that high pressure stage II, the gas is further compressed and flows into the "low" pressure stage III of the next downstream compressor 204 where it is compressed again. From the "low" pressure stage III of the downstream compressor 204, the gas flows to the high pressure stage IV of that downstream compressor 204 it is (further) compressed for a fourth time. Thus, the gas flowing through the compressor system 200 of the current embodiment undergoes four stages of compression by a balanced compressors 202 and 204 and can therefore undergo demonstrated compression ratios of up to at least 400:1.

[0041] With continuing reference to Fig. 2, the compressor system 200 comprises the pair of compressors 202 and 204 and their hydraulic cylinders 208, pneumatic cylinders 210 and 212, rods or drive shafts 214 and 216, pistons 218, and 222, and check valves 226 and 228. Each compressor 202 and 204 further comprises a pair of a low pressure stages 230, a pair of a high pressure stages 232, and a drive stage 234. The drive shafts 214 and 216 provide the motive power to drive the low and high pressure stages 230 and 232 respectively of each compressor 202 and 204 and can be driven in parallel (as demonstrated in working prototype) or series.

[0042] Focusing now on compressor 202, the hydraulic cylinder 208 is situated between and coupled to the pair of pneumatic cylinders 210 for the low pressure stages 230. Furthermore, on either end of the compressor 202, the pneumatic cylinders 212 for the high pressure stages 232 extend from, and couple to, the pneumatic cylinders 210 for the low pressure stages 230. Indeed, the cylinders 208, 210, and 212 for the compressor 202 can be formed individually and then welded together or otherwise joined to form an integral unit.

[0043] The drive shaft 214 extends through the cylinders 208, 210, and 212. Except that its length is short enough (compared to the operative lengths of the cylinders 208, 210, and 212) that it can travel freely for its full stroke. In this manner it can substantially clear one end of all of the pneumatic cylinders (low pressure) 210 and 212 (high pressure) of gas during its cycle while substantially filling the other ends of the pneumatic cylinders 210 and 212 with gas. Note also, that the drive shaft 214 carries the pistons 218, 222, and 224 which are situated in the hydraulic cylinder 208, low pressure pneumatic cylinder 210, and high pressure pneumatic cylinder 212 respectively. Furthermore, the pistons 218, 222, and 224 are positioned on and couple to the drive shaft 214 such that they substantially sweep the entire length of their respective cylinders during the stroke of the drive shaft 214. Thus, the operative portions of the compressors 202 of the current embodiment are integrated in a linear manner.

[0044] Hydraulic fluid flows into the hydraulic cylinder 208 (on one side or the other), it causes the hydraulic piston 218 to move responsive thereto. In turn, the hydraulic piston 218 urges the drive shaft 214 to move with it. For its part, the drive shaft 214 urges the pneumatic pistons 222 and 224 of the low and high pressure stages 230 and 232, respectively, to move with it along the common stroke length shared by these components. Moreover, because the cylinders 208, 210, and 212 and pistons 218, 222, and 224 have lengths/strokes which are the same, the compressor 202 substantially empties/fills the corresponding ends of the cylinders 208, 210, and 212 defined by the pistons 218, 222, and 224 as the drive shaft moves through its stroke.

[0045] Moreover, note that the drive shaft 214 reciprocates along its stroke repeatedly during operation. In the current embodiment, furthermore, any rotation of the drive shaft 214 about its longitudinal axis can be merely incidental. Indeed, if desired, the drive shaft 214 and one or more of the cylinders 208, 210, and/or 212 can be keyed to prevent such rotation. As a result, the bearings and/or seals 236 on the pistons and the seals 238 on (or in) the cylinders 208, 210, and 212 can be of relatively simple design to accommodate only the linear displacement of the drive shaft 214 while preventing leakage along the drive shaft 214 and between the cylinders 206, 210, and 212.

[0046] Fig. 2 also illustrates that the low pressure cylinders 210 have associated therewith check valves 226 and 228 on their pairs of inlet and outlet ports. These check valves 226 and 228 are oriented to prevent relatively high pressure gas in the discharging (or pressurized) end of the low pressure cylinders 210 from back flowing into the supply line. Similarly, the high pressure cylinders 212 also have check valves 226 and 228 on their inlet and outlet ports respectively to prevent relatively high pressure gas from the high pressure cylinders 212 from back flowing into or toward the low pressure cylinders 210. In addition, the high pressure cylinder 212 further has a pair of check valves 226 and 228 on its outlet ports. These latter check valves 226 and 228 are oriented to prevent relatively high pressure gas from other compressors 204 that might be downstream in the compressor system 200 from back flowing into the high pressure cylinder

[0047] Fig. 3 illustrates a plan view of a gas compressor. The gas compressor 302 of Fig. 3 includes a hydraulic cylinder 304, a low pressure pneumatic cylinder 306, and a high pressure cylinder 308. Each cylinder, as disclosed elsewhere herein has a common stroke (for the pistons and/or drive shaft contained therein). Thus, each cylinder 304, 306, and 308 defines a common length 11. The hydraulic and low pressure pneumatic cylinders 304 and 306 also happened to share a common diameter dl (and hence displacement volume) although their diameters could be different if desired. Thus, the pressure of the hydraulic fluid in the hydraulic cylinder (along with the difference in diameters of the respective pistons if any) determine the amount of pressure amplification between the (drive) or hydraulic cylinder 304 and the low pressure pneumatic cylinder 306.

[0048] Meanwhile, the high pressure cylinder 308 defines another diameter d2 which further defines (along with the diameter dl of the low pressure cylinder 306) the amount of pressure amplification between the low and high pressure cylinders 306 and 308 respectively. Of course, those of ordinary skill in the art will appreciate that while the diameters dl and d2 shown are "outside" diameters, it is the inner (or piston) diameters of the cylinders that determine the pressure amplification between the respective cylinders.

[0049] Fig. 3 also shows pipes 310, 312, 314, 316, and 318 or other fluid conduits (for instance, flex hoses, tubes, etc.) which interconnect the cylinders 304, 306, and

308. In the case of pipes 310 and 312, and when the compressor is operating in the particular direction C shown by an arrow, the pipe 310 supplies relatively high pressure hydraulic fluid to the hydraulic cylinder 304 while the pipe 312 drains relatively low pressure hydraulic fluid from the hydraulic cylinder 304. Again, with the compressor operating in direction C, pipe 314 supplies relatively low pressure gas to the low pressure cylinder 306 while pipe 316 directs pressurized gas from the discharging (or pressurized) side of the low pressure cylinder 306 to the inlet of the high pressure cylinder 308. Pipe 318 directs high pressure gas from the high pressure cylinder 308 to its point of use, distribution, another compressor 304, etc. Of course, it is recognized that a user might want the compressor 302 to operate in the opposite direction of direction C. And, therefore, Fig. 4 illustrates the piping which would allow it to do so and in many embodiments, compressors 302 would have both sets of pipes (and corresponding inlet/outlet ports).

[0050] Fig. 4 illustrates a plan view of another gas compressor. Pipe 320 supplies the other end of the low pressure cylinder 306 with relatively low pressure gas while pipe

322 directs the relatively high pressure gas from the other end of the low pressure cylinder 306 to the other inlet of the high pressure cylinder 308. Pipe 324 directs the pressurized gas from the other end of the high pressure cylinder 308 to its point of use and/or elsewhere. And, again, it is noted that compressors 302 of many embodiments would be interconnected with both sets of pipes 314, 316, 318, 320, 322, and 324.

Furthermore, check valves 226 and 228 (see Fig. 2) could be included to prevent back flow between various points. Thus, the compressors 302 of embodiments operates with its drive shafts (internal and therefore not shown) reciprocating in linear directions C and D.

[0051] Fig. 5 illustrates a perspective view of a gas compressor with inter-stage cooling features. More specifically, Fig. 5 illustrates a compressor 502 (its hydraulic cylinder 504 and low and high pressure pneumatic cylinders 506 and 508) and interstage cooling applied to its inter-stage pipe 516 and 522 via cooling jackets 528 and 532 respectively. The cooling jackets 528 and 532 can be in close thermal communication with the pipes 518 and 522 so that heat from (the gas in) the pipes 518 and 522 can flow therefrom to the cooling jackets 528 and 532. If desired, thermal grease or some other thermally conductive material can be applied between the pipes 516 and 522 and cooling jackets 528 and 532 to improve the inter-stage cooling associated with the compressor 502. Note, that such inter-stage cooling can reduce the amount of work performed by the high pressure stage thereby making the compressor 502 more efficient than it would be otherwise. The lower resultant temperatures of the gas and the high pressure stage will also likely result in improved reliability of the compressor 502 since it will operate at a lower temperature thereby stresses its components to a lesser degree.

[0052] Fig. 6 illustrates a top plan view of a compressor in a cooling tank. More specifically, Fig. 6 illustrates a compressor 602 of another embodiment and its cylinders 604, 606, and 608 along with a set of pipes 610 connecting the ends of the pneumatic cylinders 606 and 608. Additionally, Fig. 6 shows the entire compressor

602 and its set of pipes 610 (and check valves 626 and 628) immersed in a cooling tank 640 filled with a coolant 611. That coolant can be water, Freon® (if pressurized or the evaporating/boiling Freon® is dealt with in an appropriate manner), or some other fluid compatible with the compressor 602 and its associated piping and which is suitable for removing heat from the same.

[0053] Note also, that Fig. 6 illustrates that the compressor 602 and its set of piping can be treated as a sealed unit which is capable of being used in hazardous areas. For instance, because it includes no high voltage components, the entirely mechanical compressor 602 of the current embodiment could be considered intrinsically safe for NEC (National Electric Code) purposes particularly if its maximum external temperature is held within the appropriate temperature limit(s) of the NEC, applicable portions thereof, and/or other similar codes.

[0054] Fig. 7 illustrates a control system for a pair of compressors. An instrument and control system 750 of embodiments controls the compressors 702 and 704 to synchronize the operation of the two compressors 702 and 704. Of course, the system

700 could include more/fewer compressors 702 and/or 704, other types of compressors, and/or other components. For instance two-phase flow separators, relief valves, storage tanks, surge suppressors, etc. can be included in the system 700 of the current embodiment without departing from the scope of the disclosure. More specifically, though, the illustrated system 700 comprises the control system 750, distal position sensors 752, proximal position sensors 754, pipes 756, pipes 758, a control valve 760, a controller 762, a tank 764, a pump 766, cooling jackets 768, and temperature sensors 770.

[0055] With continuing reference to Fig. 7, the controller 762 could be any type of controller such as a microprocessor, an EPROM (Electronically Programmable Read Only Memory), an EEPROM (Electronically Erasable Programmable Read Only Memory) a RISC (Reduced Instruction Set Controller), an analog circuit, a relay ladder logic controller, a PLC (Programmable Logic Controller), a DCS (Distributed

Control System) controller, etc. without departing from the scope of the disclosure. The control system 750 senses the position of the drive shafts 714 and 716 via the position sensors 752 and 754; responsive thereto, it drives the pump 766 to control the compressors 702 and 704, and it senses the temperature of the compressors 702 and 704 via the temperature sensors 770 (and responds accordingly).

[0056] In the current embodiment, the position sensors 752 and 754 are shown as being positioned near the distal and proximal ends of the compressors 702 and 704. Moreover, they are configured to sense when the respective drive shafts 714 and 716 have reached their fully extended (in both directions) positions. However, the positions sensors 752 and 754 could be analog sensors which are configured to sense the continuous position of the drive shafts 714 and 716 along their entire stroke. They are, of course, in communication with the controller 762 and could be any type of position sensor. For instance, these sensors could be Hall Effect Sensors, variable resistance position sensors, fiber optic sensors, sonar/radar sensors, etc. without departing from the scope of the disclosure.

[0057] With ongoing reference to Fig. 7, the control valve 760 directs the flow of hydraulic fluid driving the compressors 702 and 704 in one direction or another. In the current embodiment, a common control valve 760 serves all of the compressors 702 and 704 in the system 700 although individual control valves 760 could be used for the individual compressors 702 and 704. Meanwhile, the tank 764 holds a reservoir of hydraulic fluid for use in driving the compressors 702 and 704. It could, of course, be any sort of tank capable of holding the hydraulic (or other working) fluid and could include means to cool the fluid therein. This tank 764, in the current embodiment, is in communication with the pump 766 and/or the control valve 760.

[0058] As to the pump 766, it provides the motive force to drive the hydraulic fluid and, of course, the pistons 718 and the compressors 702 and 704. It could be an electrically, mechanically, hydraulically, pneumatically, etc. drive pump 766 and could be remote from the compressors 702 and 704. In many embodiments, the pump 766 is a centrifugal pump although positive displacement pumps can be used with appropriate over-pressure devices.

[0059] If the compressors 702 and 704 are in a relatively hazardous and/or inaccessible environment, furthermore, the pump 766 (and/or other control system

750 components) could be located in a relatively safe and/or accessible area. Thus, should maintenance be desired on the control system 750, its components (or at least many of them) would be readily accessible. If the control system 750, or any portion thereof, is not (NEC or otherwise) intrinsically safe, such components can be located in areas which do not make intrinsic safety desirable. Similarly, 1) if any control system 750 components are incompatible with submersion and/or 2) the compressors 702 and/or 704 might be (or might become submerged), such control system 750 components can be located in an area(s) where submersion is unlikely.

[0060] With continuing reference to Fig, 7, systems 700 of the current embodiment also comprise the cooling jackets 768. These cooling jackets 768 can be positioned about the compressors 702 and 704, their high pressure stages, their inter-stage piping, etc. to cool the compressors 702 and 704 and/or the gases being compressed therein. The cooling jackets 768, moreover, can be supplied with a flow of coolant or they could be "bath" type cooling jackets with/without make-up coolant reservoirs/systems.

[0061] Moreover, the cooling jackets 768 could be instrumented with one or more temperature sensors 770 to provide for detection of the coolant temperature. Additionally, or in the alternative, the compressors 702 and 704 could be instrumented with one or more temperature sensors 770 to allow the controller to sense their temperatures and/or that of the gases therein. More specifically, the stages of compression which are positioned downstream in the system 700 could be instrumented with temperature sensors 770 although any/all of the compression stages could be so instrumented. [0062] In many embodiments, the controller 762 senses the temperatures of the compressors 702 and 704, their stages, the inter-stage piping, the gases therein, the coolant, etc. via the temperature sensors 770. And, if desirable, the controller 762 could take action responsive thereto. For instance, if a temperature associated with one or more of the compressor exceeds a user-selected threshold, the controller 762 could decrease the speed with which it drives the pump 766 (and hence the compressors 702 and 704) thereby reducing the rate of heat generation during the compression of the gases. Alternatively, if the compressor temperatures are relatively low, the controller 762 could increase the rate of compression. In addition, or in the alternative, if the cooling jacket temperature 768 exceeds/falls below some threshold, the controller 762 could increase/decrease the flow of coolant, increase/decrease the rate of compression, etc.

[0063] In operation, therefor, the controller 762 could sense the positions of the drive shafts 714 and 716. And, if they are in some intermediate position (and moving in a particular direction, the controller 762 could take no action until/unless something changes. For instance, one or more of the position sensors 752 and/or 754 could indicate that the corresponding drive shaft 714 or 716 has reached either the distal or proximal end of its stroke. Responsive thereto, the controller 762 could continue to wait until the other positon sensor 752 or 754 respectively indicates that the other drive shaft 716 or 714 has reached a corresponding position. Thus, the controller 762 could continue driving the as-yet fully extended drive shaft until it reaches that corresponding position. When that condition becomes true, all of the compressors 702 and 704 (and their stages) will have reached their fully discharged (indrawn) conditions depending on the end of the stage under consideration. Note that the system 700 could include control valves to allow the controller 762 to isolate stages which have reached their desired stroke lengths) from being driven by the hydraulic fluid while awaiting the other stages to reach that stroke length also.

[0064] Responsive thereto, the controller 762 could switch the position of the control valve 760. In so doing, the controller 762 causes the hydraulic fluid driving the hydraulic pistons 718 to reverse flow thereby driving the hydraulic pistons 718 in the opposite direction from which they had been traveling. This control action, of course, causes the compressors 702 and 704 to reverse direction and begin (for at least this cycle) compressing gas with the ends of their stages that had been previously drawing gas into themselves. When the positions sensors 752 and/or 754 indicate that the drive shafts 714 and/or 716 have reached their fully extended position (in the opposite direction), the controller 762 could again switch control valve 760 thereby causing the compressors 702 and 704 to again reverse direction. Of course, the controller 762 could continue controlling the compressors 702 and 704 in such a manner until some time limit has been reached, a particular mass of gas has been compressed, etc.

[0065] Fig. 8 illustrates a compressor with concentrically arranged compression stages. Such concentric compressors 802 can be used where accommodating the length of a non-concentric compressor might be undesirable. But, they can be used in other situations as well. Yet, the stages of concentric compressors 802 of the current embodiment can exhibit a high degree of integration in that (at least) the stroke lengths of their stages would be the same and they could be arranged/assembled in a "Russian Doll" like fashion with the smaller displacement, volume, high pressure stages near the center and the larger volume, low pressure stages near the periphery. In this manner, the low pressure stages could take advantage of the larger diameter near the periphery to accommodate their larger volumes. And the relatively low pressure stage 830 could provide structure to resist and/or to contain the relatively higher pressures in the high pressure stage 832. Although, other arrangements are within the scope of the disclosure. Note that Fig. 8 also illustrates the concentrically arranged low-pressure piston 822 and high-pressure piston 824 and their respective drive shafts 814 and 816.

[0066] Fig. 9. Illustrates a flowchart of a method in accordance with embodiments. The method 900 includes a number of operations further comprising determining the initial conditions of the gas(es) to be compressed. See reference 902. These initial conditions, of course, include, the inlet pressure of the gas, the volume (and/or volumetric flow rate) of the gas, its gas constant "R," its temperature, etc. and/or the ranges of the same. Note that since compressors of embodiments resemble positive displacement pumps, they will be relatively tolerant of changes in the composition/conditions of the incoming gas. Yet, these factors can be considered in method 900.

[0067] Method 900 also comprises determining the desired discharge conditions for the gas to be compressed. For instance, a particular discharge pressure might be desired. The temperature of the discharged gas might also be a factor and can be considered as illustrated at reference 904. As indicated at reference 906, the number of stages of compression, the number of compressors, whether they are to be connected in parallel, series, or some combination to achieve the desired discharge conditions can be determined. Also, in conjunction with the selection of the number of stages, the stroke lengths and/or displacement volumes of the various stages selected can be determined (see reference 908). Also, depending on the desired compression ratio, it might be the case that two-phase flow might occur at points in the system to be designed. If so, two-phase flow separators and/or other associated equipment can be considered for inclusion in a particular compression system. Moreover, that compression system can then be assembled as reference 910 illustrates.

[0068] As Fig. 9 shows, method 900 can continue with the pistons of the various compressors being driven to compress the supplied gas. It is noted at this juncture that the various pistons 718, 722, and 724 are double acting and will compress gas in one end of the respective cylinders and draw gas into the other end of the respective cylinders as indicated at reference 914. More specifically, the control valve 760 can be positioned (depending on the position of the drive shafts 714 and 716) to drive the compressors in parallel. Thus, as indicated at references 916 and 918, the compressors 702 and 704 will begin compressing gas in a first set of the ends of the compressor stages I to VIII and drawing gas into the second set of ends of the compressor stages I to VIII. At some time, the position sensors 752 and 754 will beginning indicating that the drive shafts 714 and 716 have reached their fully extended position in one of the two directions in which they travel. See reference 921.

[0069] Once all of the position sensors 752 and 754 indicate that all of the drive shafts 714 and 716 have reached their fully extended positions, the controller 762 can operate the control valve 760 to reverse the direction of the compressors 702 and 704. In the alternative, it might be the case that a user desires the compressors to have some stroke length less than the full length available. In which case, the controller 762 can reverse the compressors 702 and 704 when the position sensors indicate that the drive shafts 714 and 716 had reached a position corresponding to the desired stroke length. Thus, the pump 766 can drive the pistons 718, 722, and 724 back the other way. [0070] As indicated at references 920 and 922, the compressors 702 and 704 will begin compressing gas in the second set of the ends of the compressor stages I to VIII and drawing gas into the first set of ends of the compressor stages I to VIII. Of course, should one of the temperature sensors 770 indicate an over (or under) temperature condition, the controller 762 can throttle compressor system 700 down (or up) to regulate the temperatures in the system 700 (see reference 926). Moreover, reference 928 indicates that method 900 can be repeated in whole or in part (and/or even in differing orders). Thus, gas can be compressed in accordance with embodiments as method 900 illustrates.

[0071] Fig. 10 illustrates a block diagram of a controller for one or more compressors.

A few words might now be in order regarding the controllers and/or computer(s) 1006 and/or other systems, apparatus, etc. used to control compressors of embodiments. The type of computer 1006 used for such purposes does not limit the scope of the disclosure but certainly includes those now known as well as those which will arise in the future. But usually, these computers 1006 will include some type of display 1008, keyboard 1010, interface 1012, processor 1014, memory 1016, and bus 1018.

[0072] Indeed, any type of human-machine interface (as illustrated by display 1008 and keyboard 1010) will do so long as it allows some or all of the human interactions with the computer 1006 as disclosed elsewhere herein. Similarly, the interface 1012 can be a network interface card (NIC), a WiFi transceiver, an Ethernet interface, etc. allowing various components of computer 1006 to communicate with each other and/or other devices. The computer 1006, though, could be a stand-alone device without departing from the scope of the current disclosure.

[0073] Moreover, while Fig. 10 illustrates that the computer 1006 includes a processor 1014, the computer 1006 might include some other type of device for performing methods disclosed herein. For instance, the computer 1006 could include (or be) a microprocessor, an ASIC (Application Specific Integrated Circuit), a RISC (Reduced Instruction Set IC), a neural network, etc. instead of, or in addition, to the processor 1014. Thus, the device used to perform the methods disclosed herein is not limiting.

[0074] Again with reference to Fig, 10, the memory 1016 can be any type of memory currently available or that might arise in the future. For instance, the memory 1016 could be a hard drive, a ROM (Read Only Memory), a RAM (Random Access Memory), flash memory, a CD (Compact Disc), etc. or a combination thereof. No matter its form, in the current embodiment, the memory 1016 stores instructions which enable the processor 1014 (or other device) to perform at least some of the methods disclosed herein as well as (perhaps) others. The memory 1016 of the current embodiment also stores data pertaining to such methods, user inputs thereto, outputs thereof, etc. At least some of the various components of the computer 1006 can communicate over any type of bus 1018 enabling their operations in some or all of the methods disclosed herein. Such buses include, without limitation, SCSI (Small Computer System Interface), ISA (Industry Standard Architecture), EISA (Extended Industry Standard Architecture), etc., buses or a combination thereof. With that having been said, it might be useful to now consider some aspects of the disclosed subject matter. That being said, when such computers are programmed in accordance with embodiments they cease being generic computers and become computers specifically configured to perform methods in accordance with the current disclosure.

[0075] Thus compressors, compressor systems, and related apparatus and systems have been disclosed herein. Compressors of some embodiments have variable stroke lengths which allow users to vary the flow rate and compression ratios of the various compressor systems, compressors, and/or their compression stages. Moreover, the linear/reciprocating drive shafts of embodiments avoid the load restrictions which rotating compresses must endure due to their angular momentum and/or the centripetal/centrifugal forces developed thereby. Furthermore, compressors of embodiments are intrinsically safe and can be used in hazardous areas and or areas in which they might be or become submerged. In many embodiments, the various stages of the provided compressor(s) can be synchronized via their common drive shafts. Moreover, relatively smooth output flow rates can be achieved by using independent modular compressors connected in parallel and/or series. Furthermore, compressors of embodiments can be hydraulically, pneumatically, magnetically, etc. driven.

[0076] Fig. 11 illustrates a multi-stage compressor of embodiments. Generally, Fig. 11 shows a two-stage compressor with a common reciprocating shaft driving both stages. The compressor shown in Fig. 11 can be said to have a piston which is hollowed out on one side to create an internal coolant chamber along with cooling surfaces/heat fins surrounding that coolant chamber. Moreover, that hollowed out area can be defined by a cylinder which helps form one of the displacement volumes of the compressor.

[0077] Stage 1 of this cylinder is defined by a cylinder, a piston, and a shaft operationally coupled to the piston. Stage II is defined by that same piston, another cylinder, and another displacement volume (with the shaft extending through one of the displacement volumes). Furthermore, the pump 1100 can be configured with interconnecting tubing, piping, hoses, etc. such that Stage I feeds Stage II. But, it need not be so configured. Indeed, the Stages can operate independently such that they can be configured to pump fluids independently of the size of each other's displacement volumes. And because of the linear relationship between the stages, the pump can be used in cramped quarters and/or where space is limited. Moreover the multi-stage nature of the compressor of the current embodiment allows for relatively high compression ratios across those multiple stages.

[0078] As is further disclosed herein, the cylinder of Stage II also serves as a heat exchange surface and/or heat fin for cooling the fluid that the compressor moves as well as the compressor itself. Moreover, because of the configuration of this heat fin (the Stage II cylinder) internal surfaces of Stage II are exposed directly to coolant thereby increasing the efficiency of the coolant system. Additionally, since the pressures in Stage II are greater than the pressures in Stage I, it has been found that cooling Stage II in this manner can be beneficial since the corresponding Stage II temperatures are also higher in many scenarios. The stages, of course, can be interconnected and synchronized. That synchronization can be provided by virtue of a common drive shaft and/or piston.

[0079] More specifically, though, Fig. 11 illustrates the pump 1100, a cylinder 1102, a shaft 1104, another cylinder 1106, a cylinder head 1108, piston 1110, a displacement volume 1112, another displacement volume 1114, a coolant chamber 1116, Stage I ports 1118, cylinder head 1119, Stage II ports 1120, a shaft seal 1122, piston seals 1124, cylinder seals 1126, stops 1128 and 1130, interconnecting plumbing 1132, and an alignment shoe 1134. At this juncture it might be helpful to discuss some aspects of the pump 1100 with more specificity.

[0080] On that point, the Stage I cylinder 1102 serves several functions (besides helping define the Stage I displacement volume 1112) one of which is to guide the assembly associated with the shaft 1104 (including the piston 1110 and Stage II cylinder 1106) during the stroke of the shaft 1104. Moreover, from outward appearances, it would seem to be, or form, most of the body of the pump 1100. Perhaps interestingly, in some embodiments, it reciprocates while the shaft 1104 remains stationary. With either configuration, both components reciprocate relative to each other thereby enabling the compressor/pump to compress/pump fluids therein.

[0081] Regarding the shaft 1104, and as noted, it can reciprocate relative to the Stage I cylinder 1102 thereby enabling that compression. It is operatively coupled to, and carries, the Stage II cylinder 1106 and the piston 1110 (which is common to both stages). At the proximal end of the shaft 1104, the shaft 1104 couples to a reciprocating linear/reciprocating driver (not shown) which could be hydraulic, pneumatic, motor, etc. based. More distally, the shaft 1104 extends through the Stage I cylinder head 1108 and into the Stage I displacement volume. Therein it couples to the side of the piston 1110 which pressurizes (or pumps) fluid that might be in the Stage I displacement volume 1112. For the sake of convenience, that side of the Stage I piston 1110 will be referred to hereinafter as the "shaft side" of the piston.

[0082] Furthermore, the piston 1110 couples the shaft to the Stage II cylinder 1106 so that the shaft 1104 drives it as well as the piston 1110. The shaft 1104, the piston 1110, and the Stage II cylinder 1106 can be molded as an integral unit or formed separately and assembled if desired. They can therefore move together during compressor 1100 operations.

[0083] Still with reference to Fig. 11, the Stage II cylinder 1106 operationally couples with the piston 1110 and therefore travels with it. Moreover, it couples to the side of the Stage I piston opposite its shaft side and, in the current embodiment, helps define the coolant chamber 1116. Accordingly, and herein thereafter that side of the piston 1110 can be referred to as the "coolant side." Returning to various features of the

Stage II cylinder 1106, it helps define the annular Stage II displacement volume 1114 in conjunction with the piston 1110. The Stage II cylinder 1106, in conjunction with a portion of the Stage I cylinder 1102, also forms an internal space which serves as the coolant chamber 1116.

[0084] With regard to the Stage I cylinder head 1108, it closes the Stage I displacement volume 1112 and defines the ports 1118. One of these ports can be configured as an inlet port with the other being configured as an outlet port and they can be coupled to appropriate check valves and/or flow/pressure control valves as desired. The cylinder head 1108 also couples to (and/or is formed integrally with) the Stage I cylinder 1102. Since it couples with the cylinder 1102, it will travel with the cylinder 1102 in embodiments where the cylinder 1102 reciprocates rather than the shaft 1104. Moreover, it defines an aperture through which the shaft 1104 reciprocates and a race (or races) therein for the shaft seals 1122.

[0085] Still with reference to Fig. 11, the piston 1110 also probably merits some disclosure. Generally, the piston 1110 serves to pump/compress fluids in the Stage I displacement volume 1112 and to pump/compress fluids in the Stage II displacement volume 1114 (via the outer edges of its coolant side). It also closes the coolant chamber 1116 and couples the shaft 1104 to the Stage II cylinder 1106. Furthermore, it defines races for the piston seals 1124.

[0086] As to the Stage II cylinder head 1119, it closes the Stage II displacement volume 1114 and defines (along with the cylinder 1102) the Stage II ports 1120. It also guides the Stage II cylinder 1106 and defines races for Stage II cylinder seals 1126. Fig. 11 also illustrates a pair of stops 1128 and 1130 at either end of the Stage

II displacement volume 1114. These stops 1128 and/or 1130 can be defined by the Stage II cylinder head 1119, the cylinder 1102, and/or the piston 1110 as desired. They cause the shaft assembly of embodiments to stop when the shaft 1104 (traveling toward the distal end of the pump 1100) reaches the corresponding end of its stroke. The shaft 1104 can be controlled so as to reverse at/before that point and travel back toward the proximal end where the piston 1110 and Stage I cylinder head 1108 can define the other end of its stroke. Again, the shaft 1104 can be controlled to stop at efore that point with the aid of appropriate position sensors and/or other instrumentation/effectors.

[0087] The seals of course play a role in the operation of the pump 1100 as well. For instance, the shaft seals 1122 prevent fluid from escaping from the Stage I displacement volume 1112 along the shaft 1104 when that displacement volume 1112 is pressurized (relative to the surroundings). The inter-stage piston seals 1124 prevent fluid from the Stage I displacement volume 1112 from leaking to Stage II displacement volume 1114 when the Stage I displacement volume is pressurized relative to the Stage II displacement volume 1114. Conversely, when the Stage II displacement volume 1114 is pressurized relative to the Stage I displacement volume 1112, they prevent fluid from leaking into the Stage I displacement volume 1112. The cylinder seals 1126 prevent fluid from leaking to the surroundings when the Stage II displacement volume 1114 is pressurized relative thereto.

[0088] With ongoing reference to Fig. 11, the alignment shoe 1134 of the current embodiment is positioned at the end of cylinder 1106 at the end opposite piston 1110. It serves to keep the cylinders aligned as the shaft 1104 reciprocates. Note that while

Fig. 11 shows 2 alignment shoes 1134, a single or multiple alignment shoes 1134 are within the scope of the disclosure. Of course, where the sliding engagement of 1) the shaft 1104/Stage I cylinder head 1108, 2) Stage II cylinder head 1110/cylinder 1102, and/or 3) Stage II cylinder 1106/Stage II cylinder head 1119 provides sufficient guidance between the moving components, the alignment shoes 1134 might not desirable.

[0089] At this juncture it might also be helpful to consider the displacement volumes 1112 and 1114 and the coolant chamber 1116. The Stage I displacement volume 1112 is defined by the Stage I cylinder 1102, cylinder head 1108, and piston 1110. The shaft 1104, by its presence therein also helps define the displacement volume

1112 by detracting from the volume available for the pumped/compressed fluid. Meanwhile, the Stage II displacement volume 1114 is defined by (the outer edges of) the piston 1110, the Stage II cylinder 1106, and the cylinder 1102. The coolant chamber 1116, meanwhile, is defined by inner portions of the piston 1110 and the Stage II cylinder 1106.

[0090] These volumes vary with the stroke of the shaft 1104 stroke (or the stroke of the cylinder 1102 in embodiments in which it reciprocates). For instance, as the shaft moves toward the distal end of the pump 1100, the Stage I displacement volume 1112 increases, the Stage II displacement volume 1114 decreases, and (assuming a relatively stationary piston is located therein) the coolant chamber 1116 volume decreases as well. Thus, fluid is drawn into the Stage I displacement volume 1112 and pumped out/compressed in the Stage II displacement volume 1114. In the meantime, coolant in the coolant chamber 1116 is pumped out of the coolant chamber 1116. But, the coolant chamber 1116 can be open to a bath (or other source) of coolant. The motion of the pump, therefore, causes at least some convective cooling of the second stage of pumps of the current embodiment. When the shaft driver drives the shaft 1104 toward the proximal end of the pump 1100, the Stage I displacement volume 1112 decreases, the Stage II displacement volume 1114 increases, and the coolant chamber 1116 volume increases. Accordingly, fluid is pumped out of/compressed in the Stage I displacement volume, drawn into the Stage II displacement volume, and coolant is drawn into the coolant chamber 1116.

[0091] In operation, therefore (and keeping in mind that Stage I can feed Stage II via interconnecting plumbing 1132), a particular cycle of the pump might occur as follows. Assuming that the shaft 1104 begins at the distal end of its stroke and is driven in the proximal direction, fluid in the Stage I displacement volume 1112 is compressed/pumped out of one of the ports 1118 to the ports 1120 of Stage II. Stage II, meanwhile, draws that fluid into itself while the coolant chamber 1116 draws coolant into itself. Thus, the pump 1100: 1) pumps/compresses fluid in Stage I, 2) primes Stage II, and 3) draws relatively fresh/cool coolant into the coolant chamber 1116 during this phase. At some point, the shaft 1104 reverses direction, perhaps due to controller action responsive to shaft position data as the shaft 1104 approaches the proximal end of its stroke. As a result, the pump draws fluid into the Stage I displacement volume 1112 via ports 1118 while fluid is compressed in/pumped out of the Stage II displacement volume 1114. The piston 1110, meanwhile, pushes coolant out of the coolant chamber 1116.

[0092] Accordingly, two actions have occurred during this particular cycle of the pump 1100. Fluid has been pumped/compressed by Stages I and II and coolant has been circulated through the coolant chamber 1116 and/or the hollowed out (coolant side) end of the piston 1110. Note that the coolant flows through the coolant chamber 1116 which is internal to the pump 1100 and, indeed, internal to Stage II. Thus, coolant can be applied to both the external surfaces of Stage II (those on cylinder 1102 as well as the external surfaces of Stage I) and the internal surfaces of Stage II (those on cylinder 1106). Moreover, coolant can be applied to piston 1110 which comes is in thermal communication with fluids in both the Stage I and Stage II displacement volumes 1112 and 1114. This configuration of the current embodiment, therefore supplies abundant cooling to Stage I and especially the relatively higher pressure/temperature Stage II.

[0093] Accordingly, embodiments provide increase cooling over pumps/compressors heretofore available. In some embodiments the cooling chamber is open at its distal end (or elsewhere) such that ambient air, water, or other fluids can reach its interior surfaces and cool the piston 1110, the Stage II cylinder, and (hence) the Stage II displacement volume 1114 and/or the fluids therein. In other embodiments, the coolant chamber 1116 is closed and/or pressurized. Thus, to the extent that the coolant chamber 1116 is pressurized, it can structurally stabilize the walls of the Stage II cylinder 1106 adjacent to the Stage II displacement volume 1114 thereby enabling a thinning of those walls (with an attendant increase in cooling efficiency).

[0094] Fig. 12 illustrates another multi-stage pump of embodiments. Generally, in this embodiment, the shaft couples with the piston on its coolant side and does not detract from the displacement volume associated with the first stage. Rather, the shaft extends through the coolant chamber thereby allowing greater pumping capacity for the first stage. It also allows for a simplified first stage cylinder head that has no shaft aperture nor its associated seals. Moreover, the shaft 1204 can be outfit with heat fins extending radially therefrom to provide increased cooling for Stage I via the piston 1210. Note that the Stage II cylinder 1206 can also define, include, and/or comprise heat fins extending radially inward therefrom to provide increase cooling capacity for Stage II.

[0095] More specifically, the pump 1200 comprises a cylinder 1202, a shaft 1204, another cylinder 1206, a first stage cylinder head, a piston 1210, a first stage displacement volume 1212, a second stage displacement volume 1214, a coolant chamber 1216, and a second stage cylinder head 1219. Fig. 12 also illustrates Stage I ports 1218, Stage II ports 1220, a piston seal 1224, a cylinder seal 1226, a stop 1228, a stop 1230, plumbing 1232, and alignment shoe 1234. As noted, pumps 1200 of the current embodiment have increased pumping capacity due to the shaft 1204 being positioned to extend through the coolant chamber 1116 rather than the first stage displacement volume 1212. In the alternative, or in addition, the pump 1200 can provide an increased compression ratio since the Stage I displacement volume is less than it would otherwise be while the Stage II displacement volume is less than it would otherwise be. In some embodiments, furthermore, the shaft 1204, being in the coolant chamber 1216 can act as and/or be configured as a heat fin thereby providing more cooling capacity than might otherwise be the situation.

[0096] Fig. 13 illustrates yet another multi-stage pump of embodiments. Generally, the pump 1300 of the current embodiment comprises a mixture of cylinder/piston- based stages and what will be deemed herein "plunger" based stages. The plunger stages enjoy increased structural stability in that any longitudinal buckling forces that might be experienced by the shaft are minimized by virtue of the relationship between the varying pressure thereon and the varying buckling length of the plunger. Meanwhile any forces acting on the plunger in directions perpendicular to the longitudinal axis thereof are balanced and thus negated.

[0097] More specifically, the pump 1300 of the current embodiment comprises/defines a cylinder 1302, a shaft 1304, a piston 1310, a cylinder head 1330, and a displacement volume 1312 of a first stage. The pump 1300 also comprises/defines a second stage with a cylinder 1306, a corresponding displacement volume 1314, a cylinder head 1319, a plunger 1346, and a seal 1342. The common shaft 1304 is driven in a reciprocating, linear fashion as disclosed elsewhere herein.

But, it does carry the piston 1310 as the latter slidably engages the cylinder 1302. In the current embodiment, a portion of the shaft 1304 forms the plunger 1346. The plunger 1346 can have an outer diameter which is the same as the rest of the shaft 1304 although in some embodiments the two diameters differ. Yet, the plunger 1346 reciprocates in, and slidably engages, the cylinder 1306. Since the displacement volumes 1312 and 1314 can be in fluid communication with one another via interconnecting plumbing 1332, the pump 1300 can be configured as a two stage compressor its first stage being associated with displacement volume 1312 and its second stage being associated with displacement volume 1314.

[0098] The plunger 1346, as noted elsewhere herein, enjoys certain structural advantages over heretofore available pump stages. Notably, the seals 1342, which are located in races in the second stage cylinder head 1319 play a role in this stability. More particularly, they are located at the distal base of the plunger 1346 (in the second stage cylinder head 1319) when it is extended near/at the proximal end of its stroke.

[0099] This arrangement leaves a portion 1340 of the shaft 1304 that extends from the first stage piston 1310 to the seals 1342 (which are stationary in the second stage cylinder head 1319). As a result, that portion of the shaft experiences a compressive force which is the resultant force exerted on the shaft by the fluid in the first stage displacement volume 1312 (acting on the piston 1310) and the fluid in the second stage displacement volume 1314 (acting on the distal end of the plunger 1346). That resultant force places the portion 1350 under a compressive force (at times) which tends to cause a buckling moment in the portion. But, as the shaft 1304 moves proximally and even though the pressure in the second stage displacement volume 1314 increases (and the pressure in the first stage displacement volume 1312 decreases), the buckling length 1 decreases. Contra-wise, as the shaft moves distally, the buckling length 1 increases but the pressure in the second stage displacement volume 1314 increases (with the pressure in the first stage displacement volume increasing). The net result is that the compressive force acting on that portion of the shaft 1350 and the buckling length 1 of that portion are balanced more or less across the stroke of the shaft 1304. Thus, the maximum buckling moment on that portion of the shaft is minimized or at least lessened in comparison to pumps with seals that travel with the shaft and/or second stage portions thereof. This decreased shaft buckling moment can convey a number of features to the pump 1300. For one thing, the shaft 1304 tends to bend/buckle/warp less. Friction between the shaft and the cylinder walls is therefore decreased with improved efficiency as a result. Additionally, and/or in the alternative, the pump 1350 of embodiments can achieve increased compression ratios, operational speeds, etc. as compared to heretofore available pumps.

CONCLUSION

[00100] Although the subject matter has been disclosed in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts disclosed above. Rather, the specific features and acts described herein are disclosed as illustrative implementations of the claims.