FLUID PUMP HAVING HIGH PRESSURE METERING AND HIGH

PRESSURE DELIVERING

BACKGROUNDART

[0001] The present invention relates to high-pressure fluid pumps.

[0002] Delivering under high pressure is useful, for example, in liquid chromatography to pump the mobile phase (e.g. a mixture of solvents) through the chromatographic system including the separation column. The pumping apparatus may form a part of a solvent delivery system which then comprises additional units for drawing in and mixing solvents.

[0003] Different approaches are known in the art for pumping the mobile phase through a chromatographic system. According pumping apparatuses usually require a pressure source and may comprise any possibility for blending different solvents, for example by filtering fluctuations of composition or mixing them through a certain amount of volume.

[0004] EP 0 309 59& B1 (by the same applicant), for example, shows a pumping* apparatus comprising two pistons and two according pump chambers and control means coupled to drive means for adjusting the stroke length of the pistons.

[0005] A combination of a pump producing a pulsating stream of liquid such as a diaphragm pump and a pulse damper is disclosed the EP 0 115672 B1 (by the same applicant).

[0006] US 4,003,679 (by the same applicant) discloses a pumping system provided in which a low pressure metering pump injects fluid charges into a high pressure pump which in turn operates into a high pressure load.

[0007] US 4,599,049 (by the same applicant) discloses a high pressure meter pump system with improved accuracy by subdividing a large meter pump capacity into metered subvolume charges which are incrementally delivered to a high pressure

slave pump.

[0008] Another system is shown in the US 4,714,545 (by the same applicant), wherein a plurality of fluid solutions are connected to an input of a pump system having at least two displacement chambers.

DISCLOSURE OF THE INVENTION

[0009] It is an object of the invention to provide an improved delivery of fluid. The object is solved by the independent claims. Preferred embodiments are shown by the dependent claims.

[0010] According to embodiments of the present invention, a pumping apparatus adapted for delivering fluid against pressure is suggested. The pumping apparatus can be adapted for blending at least two different fluids, for example liquids. The pumping apparatus can be adapted for delivering the blended fluid at high pressure at which compressibility of the fluid becomes noticeable.

[0011] The pumping apparatus comprises a plurality of metering devices with at least a first metering device and a second metering device. The metering devices each comprise an inlet and an outlet. The outlets of the metering devices are coupled to an inlet θf a damping device. In other words, the metering devices caft'be connected in parallel or side-by-side. Consequently, different flows, for example flows of different fluids, can flow through the metering devices in parallel, wherein all flows of said different fluids lead into one common flow leading into the damping device.

[0012] The metering devices can deliver different fluids to the damping device at high pressure. The metering devices can be adapted for increasing the pressure of the metered fluids to said high pressure. The damping device can de designed and operated to compensate any occurring flow and thus pressure fluctuation. This makes it possible to deliver a stream of fluid at higher pressures, relatively low flow rates, and fewer pulsations.

[0013] Advantageously, miniaturized chromatographic systems, which generally need lower flow rates, higher pressures, and refined mixing ratios, can be supplied

with fluid, for example liquid, by the pumping apparatus. The pumping apparatus comprises an improve performance and can therefore enhance the performance of such coupled chromatographic systems. This is why the mobile phase can be pumped through said chromatographic systems with an increased accuracy of system parameters like flow rate and pressure. Advantageously, such coupled systems allow an increased total number of peaks per time interval. Due to the improved pumping apparatus, such coupled systems can comprise one or more of the following features for enhancing the performance: Smaller size of packing material, smaller id columns, faster linear speed of solutions during separation, faster compositional gradients, and longer separations beds. Summarizing, the total amount of liquid in use can be reduced without seriously endangering the quality of the separation process.

[0014] For chromatographic analysis, for example, a flow rate of fluid can be delivered to the column by the pumping apparatus being adjustable across a wide range of flow rates. Besides this, the pumping apparatus permits the generation of mixtures of solvents and changing the mixing ratio of the various solvents of the mixture in the course of time (gradient operation). Advantageously, the pumping apparatus can deliver a tunable blend of different fluids allowing an exact mixing ratio. Such versatility of the pumping apparatus allows optimizing the analysis conditions for the specific sample to be chromatographically separated.

[0015] Advantageously, the flow rate can be adjustable or selectable and can be - once selected — kept substantially constant by the damping device. This can avoid any fluctuation of the flow rate through the separation column leading to variations in the retention time and peak width of the examined sample compounds so that the areas of the chromatographic peaks produced by a detector connected to the outlet of the column, for example, an absorption detector, a fluorescence detector, or a refractive index detector, may vary.

Since the peak areas are representative of the concentration of the chromatographically separated sample substances, preventing any fluctuations in the flow rate can advantageously improve the accuracy and the reproducibility of quantitative measurements.

[0016] In a minimum configuration for blending two fluids at required composition precision, an embodiment of the pumping apparatus only needs three devices, namely the two metering devices and the damping device, and can produce a ripple free stream of tunably blended fluid against high pressure. Advantageously, this can allow a mechanically simple and cost saving design.

[0017] Embodiments may comprise one or more of the following. Advantageously, the metering devices can deliver fluid synchronously to the damping device. In preferred embodiments, the damping device is realized as an active damping device or in other words as an active pulse damper. An active pulse damper can comprise at least one correcting element for influencing at least one parameter, for example the outflow from the damper.

[0018] Advantageously, the damping device can actively stabilize the output flow and thus pressure of the pumping apparatus by being controlled in reaction to a sensing device. This makes it possible that the metering devices produce a pulsating stream of exactly blended fluid without abandoning the aim of a ripple-free output stream of blended fluid. The metering devices can concurrently produce a plurality of exactly metered streams of fluid into the inlet of the damping device. Advantageously, the streams can be blended homogenously just by transporting them into a common connection conduit to the inlet of the damping device. While sucking fresh fluid, the metering devices do not have to produce a stream of fluid because the damping device can fill this time gap by dispensing volume. This can result in a substantially ripple-free streaming out of defined amount of specific fluid composition delivered by the complete pumping apparatus.

[0019] Embodiments may comprise one or more of the following. The outputs of the metering devices can be coupled to the inlet of the damping device via a mixing device. The mixing device can comprise a certain volume for filtering the streams of the metering devices. The mixing device comprises one inlet for each of the metering devices and one common outlet coupled to the inlet of the damping device. The apparatus can comprise according connection conduits adapted for coupling the separate outlets of the metering devices each to separate inlets of the mixing device.

Possibly, the mixing device comprises a certain volume for filtering or mixing the streams produced by the metering devices. The metering devices are adapted for delivering fluid concurrently to the inlets of the mixing device.

[0020] Advantageously, the mixing device can be realized by a simple branch tee - or by a multi-branch connector having a plurality of inlets and one common outlet when more than two metering devices are employed — for avoiding any dead volume. The different fluids can be mixed exactly and simply just by delivering or metering them concurrently into the connection conduit between the outlet of the branch tee and the damping device. For reducing any dead volume to a minimum, the length of said connection conduits can be reduced to a minimum. For example, the branch tee can be integrated in the damping device.

[0021] This reduces any dead volume causing undesired side effects affecting the quality of the flow rate and/or the output pressure to a minimum. Advantageously, the volume of the damping device is structured such being useful for filtering fluctuations of composition of the inflowing blend of different fluids. By this, the damping device additionally realizes a mixing device resulting in a highly homogenous blend of the different fluids deliverable by the pumping apparatus.

[0022] Embodiments may comprise one or more of the following. The pumping apparatus is operated substantially at two different pressures: A sucking pressure and an output pressure. The metering devices each are adapted for letting in fluid at the sucking pressure and for delivering fluid, in particular to the mixing device, at the output pressure. Consequently, the metering devices are adapted for increasing the system pressure from the low sucking pressure up to the high output pressure. The mixing device and the damping device both can be operated always at output pressure. More precisely, the metering devices can be operated between the low sucking pressure and the high output pressure. The sucking pressure can be as low as 20 mbar and the output pressure can be as high as 2000 bar.

[0023] Embodiments may comprise one or more of the following. The metering devices and the damping device each can comprise a piston for reciprocation in an according pump or damper chamber. Accordingly, the pumping apparatus comprises a

valve arrangement with a plurality of valves adapted for allowing the flow of fluid into the inlets of the metering devices and the damping device or rather the according pump chambers, and for inhibiting the flow in the opposite direction. The valve arrangement can comprise one or more flow check valves, on-off valves, and/or flow control valves or any other valves suitable for this purpose. Preferably, the pump chambers or rather the inlets of the metering devices each are coupled to inlet valves adapted for allowing the flow of fluid into the pump chambers of the metering devices and for inhibiting the flow in the opposite direction. The pump chambers each are located downstream of the inlet valves.

[0024] Accordingly, the inlets of the mixing device, in particular the branch tee, are coupled to mixing inlet valves adapted for allowing the flow of fluid into the mixing device and for inhibiting the flow in the opposite direction. The inlets of the mixing device are located downstream of the mixing inlet valves. In this configuration, the outlet of the mixing device is directly coupled to the inlet of the damping device. Alternatively or additionally, the connection conduit between the mixing device and the damping device can comprise an according valve.

[0025] Embodiments may comprise one or more of the following. Advantageously, the pumping apparatus comprises a control unit. The control unit controls at least one controllable feature such as the metering devices, the damper device, and the valves of the valve arrangement. For this purpose, the control unit can communicate with the different elements in an open or closed loop mode.

[0026] For realizing an optimal feedback closed loop controller, the embodiments of the pumping apparatus can comprise one or more different sensors, such as a pressure sensor for measuring the pressure within any of the conduits of the pumping apparatus, a flow sensor for measuring the flow rate within any of the conduits of the pumping apparatus, a position sensor for measuring the position of any of the pistons of the metering devices, or any other suitable sensor using any suited method of measuring the needed system variables. Consequently, the control unit can realize, for example, a pressure controller, a position controller, and/or a flow controller for controlling the inlet pressure, for controlling the output pressure, the switching status of

any one of the valves, the position of any one of the pistons of the metering devices, the position of the pistons of the pumping devices and/or the damping device, and/or the flow within any one of the connection conduits or at the outlet of the pumping apparatus.

[0027] Advantageously, the control unit can control the damping device, in particular the movement of the piston of the damping device within the pumping or damper chamber of the damping device for realizing an active pulse damping unit in a manner that the output flow and thus pressure is substantially stabilized. Optionally, the pressure and/or the flow can be substantially stabilized. Therefore, the damping device comprises a flow and/or pressure sensor. Advantageously, this enables a smoother changeover of composed fluid from the metering devices into the damping device. In a period of constant pressure mode, the volume contraction can be measured during the time when both metering devices dispense their respective volume. Depending on the timing of dispense/reload cycles, the mixing volume can be adapted to achieve best performance at a given flow rate by running the pistons at variable stroke and frequency, whether the volume of the pump chamber of the damping device is used for filtering or mixing the inflowing fluid. A method of running pistons at variable stroke and frequency is disclosed in the EP 0309596 B1 , which is incorporated herein by reference. Advantageously, the inlet and the outlet of the damping device are positioned at the pump chamber of the damping device in a manner, that a FIFO concept is realized. Consequently, any fluid streaming into the pump chamber of the damping device through the inlet is flowing out first as well. This makes it possible to deposit a gradient in the pump chamber of the damping device, which is then dispensed to the system as a homogenous blend.

[0028] Embodiments may comprise one or more of the following. The pistons of the metering devices can be acting in synchronous fashion when individual flow rates are at comparable levels, but when flow rates differ, say e.g. 10/1, the slower moving piston may just start/stop dispensing until its volume is at a minimum limit. In other words, the slower moving piston stops for each half cycle of the faster moving piston sucking fresh fluid. The proportion of the amplitudes of the synchronous strokes of the pistons of the metering devices is substantially equal to the mixing ratio. Considering

side effects caused by the compressibility of the fluids may modulate this proportion appropriately.

[0029] Embodiments may comprise one or more of the following. For realizing an open loop controller, the control unit can comprise data of the fluids to be mixed, in particular the compressibility, used for calculating and controlling the optimal movement of the pistons of the pumping apparatus for realizing the substantial stabilized output flow and thus pressure. The data can comprise, for example, one or more of the following parameters: The compressibility of each fluid as a function of the pressure and the temperature, the compressibility of the blend as a function of the pressure and the temperature, the viscosity of the fluids and of the blend as a function of the pressure and the temperature, and the mixing volume as a function of the mixing ratio, the mixed fluids, the temperature, and the pressure. The specific volume of the fluids after blending them shall be understood herein, for example, as the mixing volume. Of special interest can be the loss or gain of volume during blending. By using the data above and calculating said loss or gain of volume during blending, any retroactive effect to the desired output pressure can be compensated by the control unit. Consequently, the control unit can calculate the optimal movement and timing of the pistons of the metering devices and the damping device. For each fluid, the control unit has to be fed with the corresponding parameters. Possibly, the control unit can realize an adaptive system, wherein the control unit measures the parameters needed during an initial phase before operating the pumping apparatus. Especially advantageously, the control unit can realize a mixture of the closed and open loop modes. Recapitulating, the control unit can realize a drive control for all metering devices and the damping device of the pumping apparatus in a manner that the output flow and thus pressure is substantially stabilized and a stream of a homogenous blend with an exactly determined mixing ratio is generated.

[0030] According to other embodiments of the present invention, a fluid separation system comprising a fluid, for example liquid, delivery system comprising a pumping apparatus as described above and a separation device for separating components of the fluid, for example liquid, delivered by the fluid delivery system is suggested. Advantageously, the pumping apparatus can produce an exact ripple-free flow of fluid,

for example liquid, for optimizing the performance of the fluid separation system.

[0031] Further embodiments of the present invention relate to a method of delivering fluid, for example at high pressure at which compressibility of the fluid becomes noticeable. In a first step, a plurality of different fluids is metered by a plurality of metering devices. Subsequently, the fluids are received from the plurality of metering devices upstream by a damping device. Finally, pressure fluctuations of the fluids metered by the plurality of metering devices are substantially compensated by the damping device. In embodiments, a pumping apparatus as described above is employed for executing the method. Advantageously, the fluids can be concurrently metered by the metering devices and the pressure can be increased up to said high pressure. Additionally, the different fluids can be mixed before the damping device receives them. Any side effects, for example occurring while blending them within the mixing device can be substantially compensated by the downstream damping device. Advantageously, the damping device does not have to increase the pressure and can be employed therefore for stabilizing the output pressure.

[0032] Embodiments of the invention can be partly or entirely embodied or supported by one or more suitable software programs, which can be stored on or otherwise provided by any kind of data carrier, and which might be executed in or by any suitable data processing unit. Software programs or routines are preferably applied for controlling the steps of the method as described above. For example, for controlling set points of the pumping apparatus or said steps by using a control unit comprising the software programs or routines, for example as firmware.

BRIEF DESCRIPTION OF DRAWINGS

[0033] Other objects and many of the attendant advantages of embodiments of the present invention will be readily appreciated and become better understood by reference to the following more detailed description of preferred embodiments in connection with the accompanied drawing. Features that are substantially or functionally equal or similar will be referred to with the same reference sign(s).

[0034] Fig. 1 shows a pumping apparatus with two metering devices and a

damping device controlled by a control unit and

[0035] Fig.2 shows a schematic view of a fluid separation system with a fluid delivery system comprising a pumping apparatus.

[0036] Fig. 1 shows a pumping apparatus 1 with a first metering device 3, a second metering device 5, and a damping device 7 controlled by a control unit 9. The first metering device of the pumping apparatus 1 comprises a first piston 11 for reciprocation in a first pump chamber 13, the second metering device 5 of the pumping apparatus 1 comprises a second piston 15 for reciprocation in a second pump chamber 17, and the damping device 7 of the pumping apparatus 1 comprises a third piston 19 for reciprocation in a damper chamber 21.

[0037] The pistons 11, 15, and 19 each are coupled to a screw link actuator 23 driven by a motor 25. The screw link actuators 23 may be coupled via a ball 27 to the metering devices 3, 5, the damping device 7 and to according return springs 29 of the devices 3, 5, and 7. These components realize three drives 31 for the metering devices 3, 5, and for the damping device 7. Drives as the drives 31 for actuating pistons for reciprocating in pump chambers are known in the art and therefore not described in detail in this application. Other embodiments may use crank drives, excenter drives or direct or indirect coupled linear motors.

[0038] The outer diameter of the pistons 11, 15, and 19 are smaller than the inner diameter of bore 33 of the respective pump chambers 13, 17, and the damper chamber 21 so that fluid can flow in the gap between the pistons 11, 15, and 19 and the inner surface of the bores 33.

[0039] Each of the devices 3, 5, and 7 comprises an inlet 35 and an outlet 37. Advantageously, the inlets 35 of the devices 3, 5, and 7 are coupled to an end off the bores 33 located upstream of the upstream inflection point of the pistons 11 , 15, and 19, wherein the outlets 37 of the devices 3, 5, and 7 are coupled to the opposite end of the bores 33 located downstream of the downstream inflection point of the pistons 11 , 15, and 19. By this, fluid sucked firstly into any one of the chambers 13, 17, or 21 can be dispensed firstly also. By this, a first-in-first-out principle can be realized.

[0040] The first pump chamber 13 of the first metering device 3 is coupled to a mixing device 39 via the outlet 37, a first connection conduit 41 comprising a first mixing inlet valve 43. The first pump chamber 13 of the first metering device 3 is located upstream of the mixing device 39. The second pump chamber 17 of the second metering device 5 is coupled to the mixing device 39 via the outlet 37 and a second connection conduit 45 comprising a second mixing inlet valve 47. The second pump chamber 17 of the second metering device 5 is located upstream of the mixing device 39. The position of the mixing inlet valves 43 and 47 within the conduit 41 and 45 may vary. In other embodiments, the mixing inlet valves 43 and 47 are positioned as close as possible to the mixing device 39.

[0041] Besides this, the mixing inlet valves 43 and 47 can be integrated in the mixing device 39 or in the metering devices 3 and 5. The mixing inlet valves 43 and 47 are adapted for allowing the flow of fluid into the mixing device and for inhibiting the flow in the opposite direction. The mixing device 39 comprises two or more inlets 49. The number of inlets 49 of the mixing device 39 is preferably equal to the number of metering devices. In embodiments, the pumping apparatus 1 can comprise an arbitrary higher amount of metering devices and according inlets 49 of the mixing device 39.

[0042] The mixing device 39 is coupled to the damper chamber 21 via an outlet 51, a third connection conduit 53 and the inlet 35 of the damper device 7. The mixing device 39 is located upstream of the damper chamber 21. The damper chamber 21 is coupled to the outlet 37 of the damping device 7. The damper chamber 21 is located upstream of the outlet 37. The stream of fluid provided by the pumping apparatus 1 is provided at the outlet 37 of the damping device 7.

[0043] In embodiments, the damping device 7 can be coupled to a pressure sensor 55 for measuring the output pressure of the pumping apparatus. The conduits 41 , 45, and 53 are operated at the output pressure.

[0044] The first pump chamber 13 of the first metering device 3 is coupled downstream to a first inlet valve 57 via the inlet 35 of the first metering device 3 and a first inlet connection conduit 59. The first pump chamber 13 is located downstream of the first inlet valve 57.

[0045] The second pump chamber 17 of the second metering device 5 is coupled to a second inlet valve 61 via the inlet 35 of the second metering device 5 and a second inlet connection conduit 63. The second pump chamber 17 is located downstream of the second inlet valve 61.

[0046] In embodiments, the inlet valves 57 and 61 can be realized as integrated valves within the metering devices 3 and 5. Consequently, in such embodiments, the pumping apparatus needs no connection conduits 59 and 63 between the valves 57 and 61 and the devices 3 and 5.

[0047] In other embodiments, the inlet valves 57 and 61 can be realized as controlled valves, for example as an on-off or a flow control valve. Forthis purpose, the valves 57 and 61 can comprise valve controllers 65, for example controlled by the control unit 9. Preferably in simple embodiments, the valves 57 and 61 are realized as simple flow check valves. Possibly, the valves 43 and 47 can be realized as on-off or flow control valves also. In preferred simple embodiments, all valves 43, 47, 57, and 61 are realized as simple flow check valves, as known in the art.

[0048] For delivering a ripple-free continuous stream of blended fluid at the outlet 37 of the damper chamber 21 of the damping device 7 of the pumping apparatus 1 , the pumping apparatus ⁵ -! can be coupled with the control unit 9 via control connections ¹ 67. The control unit 9 can realize, for example, a pressure controller 69 for the output pressure of the pumping apparatus 1 , a position controller 71 for the drives 31 for the devices 3, 5, and 7, or a flow controller 73 for the flow rates within the connection conduits 41 , 45, or at the outlet 37 of the pumping apparatus 1. For this purpose, the pumping apparatus 1 can comprise additionally not shown suitable pressures sensors, flow sensors, and/or position sensors. Besides this, the control unit 9 may communicate with encoders 75 coupled to the motors 25 of the drives 31. Each of the drives 31 comprises one drive controller 66 connected via at least one of the control connections 67 to the control unit 9. The control unit 9 interprets all data delivered by the pumping apparatus for realizing a high sophisticated drive control for the pistons 11, 15, and 19. For this purpose, the drive control unit 9 can store and/or measure relevant parameters within the connection conduits within the pumping apparatus 1 , for

example the compressibility or viscosity. Additionally, the control unit can communicate with said sensors in order to compensate any side effect caused by eventually leaking piston seals.

[0049] In order to precisely blend the composition of stream in the third connection conduit 53 respective the output connection conduit 37, the pistons 11 and 15 of the metering devices 3 and 5 are moved in phase while delivering. At the high pressures encountered in high performance liquid chromatography, compressibility of the solvents becomes noticeable resulting in an additional source of pulsation when not corrected. The reason is that during each compression cycle of the metering devices 3 and 5, the pistons 11 and 15 have to move a certain path to compress the fluid to its final output pressure before actual delivery of fluid s tarts. Advantageously, the damping device 7 can compensate this effect. Side effects caused by the change of the mixing volume and/or the viscosity of the fluids can be compensated also.

[0050] Besides this, the control unit 9 can compensate additionally any differences in the compressibility of the different fluids sucked by the metering devices 3 and 5 in a manner that the metering devices 3 and 5 deliver just concurrently fluid through the connection conduits 41 and 45 into the mixing device 39. By this, it is possible to produce a homogenous blend of the different fluids delivered by the metering devices

3 and 5 by using a simple branch tee 77 - as indicated with dashed lines -within the mixing device 39. The flow of fluid is provided at an output connection conduit 79 coupled to the outlet 37 of the damping device 7.

[0051] In other embodiments, the mixing device 39 can comprise a volume for mixing or better filtering fluctuations of composition of the different fluids.

[0052] Fig. 2 shows a schematic view of a fluid separation system 95 with a fluid delivery system 97 comprising the pumping apparatus 1 and a separation device 99 for separating components of the fluid delivered by the fluid delivery system 97. The fluid separation system 95 can comprise a detecting device 101 or a coupling 103 to the detection device 101. The detection device 101 can be employed for detecting components of the fluid separated by the separation device 99. Besides this, the fluid separation system 95 can be connected to a not shown apparatus, for example a mass

spectrograph, for analyzing the fluid, for example liquid, via a connection conduit 105. The separation device 99 can be realized, for example, as a high performance liquid chromatography chip. The pumping apparatus 1 , for example coupled to the control unit 9, can deliver a ripple-free stream of a blend of different fluids, for example a gradient of two solvents, to the separation device 99, for example the high performance liquid chromatography chip.

[0053] In the following different phases of operation of the pumping apparatus 1 are described in detail by referring to the different pressure levels and to Fig. 1 :

[0054] In a first phase, while sucking fresh fluid/s through the connection conduits 59 and 63, the metering devices 3 and 5 cannot deliver any fluid into the damper chamber 21 of the damping device 7. The valves 57 and 61 are open and the valves 43 and 47 are closed. Consequently, the metering devices are operated at the sucking pressure in this first phase. The pistons 11 and 15 of the metering devices 3 and 5 are moved - in direction of the Fig. - downwards for sucking said fresh fluids. In this condition of the pumping apparatus 1 , the piston 19 of the damping device 7 is moved - in direction of the figure - towards the top for avoiding any flow and thus pressure fluctuation. The volume of the damper chamber 21 of the damping device 7 has to be large enough for bridging the phase in which the metering devices 3 and 5 cannot deliver any fluid.

[0055] In a second phase, the pistons 11 and 15 of the metering devices 3 and 5 are moved — in direction of the Fig. — upwards for increasing the pressure within the pump chambers 13 and 17 from the sucking pressure up to the output pressure. In the second phase all valves 43, 47, 57, and 61 are closed. Consequently, the pressure in the conduits between the valves 57, 61 and 43, 47 varies between the sucking pressure and the output pressure in this second phase.

[0056] In a third phase when the metering devices 3 and 5 deliver fluid concurrently into the damper chamber 21 the piston 19 of the damping device 7 can be moved in the opposite direction for avoiding any pressure increase and for refilling the damper chamber 21. In the third phase of delivering fluid, the complete system upstream to the valves 57 and 61 is operated substantially at the output pressure. Consequently, the

valves 57 and 61 are closed and the valves 43 and 47 are open.

[0057] The control unit 9 controls the movement of all pistons 11, 15, and 19 for guaranteeing an optimal hand shake of the metering devices 3 and 5 with the damping device for guaranteeing a ripple free and constant stream of fluid delivered by the pumping apparatus 1. On account of the drive control by the control unit 9 the damping device 7 acts as an active damping device,

[0058] In a fourth phase, the pistons 11 and 15 of the metering devices 3 and 5 are moved - in direction of the Fig. - downwards for decreasing the pressure within the pump chambers 13 and 17 from the output pressure down to the sucking pressure. In the fourth phase all valves 43, 47, 57, and 61 are closed. Consequently, the pressure in the conduits between the valves 57, 61 and 43, 47 varies between the output pressure and the sucking pressure in this fourth phase.

[0059] For an optimal hand shake between the metering devices 3 and 5 and the damping device 7, the control unit 9 has to calculate the exact point of time when the valves 43 and 47 open or can be opened, for example by the control unit 9. At this point of time, the direction of movement of the third piston 19 within the damper chamber 21 of the damping device 7 has to be changed, in particular inversed. Possibly, shortly before the hand shake, the speed of the pistons 11 and 15 can be reduced for allowing a smoother hand shake. The movement of the third piston 19 of the damping device has to be modified accordingly during and after the hand shake.

[0060] During the phases three and four and the sucking phase, the output pressure and the stream of fluid are produced exclusively by the damping device 7.

[0061] The phases are repeated in the following order; first phase for sucking, second phase for increasing the pressure downstream of the valves 43 and 47, third phase for delivering fluid by the metering devices 3 and 5 under high pressure or output pressure to the damping device 7, and fourth phase for decreasing the pressure downstream of the valves 43 and 47. At the end of the second phase and at the beginning of the fourth phase, the control unit 9 has to handle the handshake and consequently to change the movement of the third piston 19 of the damping device 7

for allowing the ripple-free output stream from the pumping apparatus 1.

[0062] At the high pressures encountered, for example, in high performance liquid chromatography, compressibility of the solvents becomes noticeable resulting in an additional source of pulsation. The reason is that during each compressing cycle of the metering devices 3 and 5 the piston 11 and 15 of the metering devices 3 and 5 have to move a certain path to compress the fluids to the final output pressure before actual delivery to the mixing device 39 respectively to the damping device 7 starts. Advantageously, the damping device 7 can compensate this effect. Besides this, side effects caused by the change of the mixing volume or the viscosity of the different fluids can be compensated by the damping device 7 also. This results in a ripple-free and constant flow under high pressure at the outlet 37 of the damping device 7 respectively in the output connection conduit 79 of the pumping apparatus 1.

[0063] Recapitulating, the control unit 9 controls the movement of all pistons 11, 15 and 19 for guaranteeing an optimal handshake or better a smooth changeover of the metering devices 3 and 5 with the damping devices 7 for ensuring a ripple-free and constant stream of fluid delivered by the pumping apparatus 1. On account of the drive control by the control unit 9 the damping device 7 can act as an active damping device.

[0064] In the following a method of delivering fluid, for example at high pressure at which compressibility of the fluid becomes noticeable, for example by using a pumping apparatus of Rg. 1 or a fluid separation system of Fig. 2, is described by referring to the figures.

Firstly, a plurality of different fluids is metered with a plurality of metering devices 3, 5. After that, the fluids are received from the plurality of metering devices 3, 5, for example by the damping device 7 via the mixing device 39. The fluids can be transported from the plurality of metering devices 3, 5 into the mixing device 39, and from there into the damping device 7. Finally, fluctuations, for example flow and/or pressure fluctuations, of the fluids metered by the plurality of metering devices 3, 5 are substantially compensated by the damping device 7. The different fluids can be mixed, for example within the mixing device and/or within the damper chamber 21 of the damper device 7. The pressure of the different fluids can be increased in the metering

devices before mixing them, for example up to said high pressure. The fluids can be transported subsequently under said high pressure, for example after passing the mixing device 39, to the damping device 7. Concurrently, a control unit 9, for example comprising suited software programs or routines, can control the steps as described above.

[0065] The pumping apparatus can be coupled to a fluid separation system for analyzing and or separating fluid, more specifically, for executing at least one separation process, for example a liquid chromatographic process, for example a high performance liquid chromatographic process (HPLC). For analyzing a fluid, for example a liquid, or rather one or more components within the fluid or liquid, the coupled system can comprise a detection area, such as an optical detection area and/or an electrical detection area being arranged close to a flow path within the system. Alternatively, the fluid separation system can be coupled to a detection area or a detecting apparatus such as a mass spectrograph. The fluid separation system can be realized as a chromatographic system (LC), a high performance fluid chromatographic (HPLC) system, an HPLC arrangement comprising a chip and an mass spectrograph (MS), a high throughput LC/MS system, a purification system, micro fraction collection/spotting system, a system adapted for identifying proteins, a system comprising' a GPC/SEC column, a nanoflow LC system, and/qn a multidimensional LC system adapted for separation of protein digests, or alike. Besides this, the pumping apparatus can be a component part of a laboratory arrangement.

[0066] It is to be understood, that this invention is not limited to the particular component parts of the devices described or to process steps of the methods described as such devices and methods may vary. It is also to be understood, that different features as described in different embodiments, for example illustrated with different elements in the figures, may be combined to new embodiments. It is finally to be understood, that the terminology used herein is for the purposes of describing particular embodiments only and it is not intended to be limiting. It must be noted, that as used in the specification and the appended claims, the singular forms of "a", "an", and "the" include plural referents until the context clearly dictates otherwise. Thus, for

example, the reference to "a sensing device" or "an inlet valve" includes two or more such functional elements.