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Patent Searching and Data


Title:
GAS COMPRESSOR
Document Type and Number:
WIPO Patent Application WO/2012/092977
Kind Code:
A1
Abstract:
A high-pressure piston compressor (1) for compressing gas, comprising a vessel (4) having a vessel chamber (8, 23) wherein a piston (3) is guided reciprocally, for compressing a gas in the vessel chamber during operation of the piston compressor, an inlet valve housing (17, 29) comprising an inlet valve(18, 30), and an outlet valve housing (15, 31) comprising an outlet valve (16, 32), wherein the inlet valve housing and the outlet valve housing are mounted within a portion of the vessel chamber wall (14, 28), and wherein the portion of the vessel chamber wall encloses the inlet valve housing and the outlet valve housing, such that the portion of the vessel chamber wall generates an isostatic counter-pressure on the inlet valve housing and the outlet valve housing in response to the pressure on the inlet valve housing and the outlet valve housing from the gas in the vessel chamber during operation of the piston compressor.

Inventors:
THUNHOLM, Roger (Floragatan 4, Västerås, S-724 61, SE)
Application Number:
EP2011/050166
Publication Date:
July 12, 2012
Filing Date:
January 07, 2011
Export Citation:
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Assignee:
AVURE TECHNOLOGIES AB (Quintusvägen 2, Västerås, S-721 66, SE)
THUNHOLM, Roger (Floragatan 4, Västerås, S-724 61, SE)
International Classes:
F04B9/109; F04B9/115; F04B25/00; F04B39/10; F04B39/12
Foreign References:
EP0064481A1
DE10353314A1
US4284391A
GB2344622A8
EP0064481A1
Attorney, Agent or Firm:
LOQVIST, Mathias (Awapatent AB, Box 45086, S- Stockholm, 104 30, SE)
Download PDF:
Claims:
CLAIMS

1 . A high-pressure piston compressor (1 ) for compressing gas, comprising

a vessel (4) having a vessel chamber (8, 23) wherein a piston (3) is guided reciprocally for compressing a gas in the vessel chamber during operation of the piston compressor,

an inlet valve housing (17, 29) comprising an inlet valve (18, 30) for controlling a supply of gas into the vessel chamber, and

an outlet valve housing (15, 31 ) comprising an outlet valve (16, 32) for controlling a discharge of gas out from the vessel chamber,

wherein the inlet valve housing and the outlet valve housing are mounted within a portion of the vessel chamber wall (14, 28), and wherein the portion of the vessel chamber wall encloses the inlet valve housing and the outlet valve housing, such that the portion of the vessel chamber wall generates an isostatic counter-pressure on the inlet valve housing and the outlet valve housing in response to the pressure on the inlet valve housing and the outlet valve housing from the gas in the vessel chamber during operation of the piston compressor.

2. The piston compressor as claimed in claim 1 , further comprising an inlet duct (20, 33) mounted at least partially within the portion of the vessel chamber wall for allowing a supply of gas into the vessel chamber, wherein the inlet valve housing is positioned within the inlet duct and positioned immediately adjacent the vessel chamber.

3. The piston compressor as claimed in claim 2, wherein the inlet duct elongates to the vessel chamber substantially in parallel with the vessel axis.

4. The piston compressor as claimed in any one of the preceding claims, further comprising an outlet duct (19, 34) mounted at least partially within the portion of the vessel chamber wall for allowing a discharge of gas out from the vessel chamber, wherein the outlet valve housing is positioned within the outlet duct and positioned immediately adjacent the vessel chamber.

5. The piston compressor as claimed in claim 4, wherein the outlet duct elongates from the vessel chamber substantially in parallel with the vessel axis. 6. The piston compressor as claimed in any one of the preceding claims, wherein the portion of the vessel chamber wall is a block unit, detachable from the piston compressor.

7. The piston compressor as claimed in claim 6, wherein the block unit is fastened by a threaded nut (21 ), the block unit being positioned between the threaded nut and the vessel chamber.

8. The piston compressor as claimed in any one of the preceding claims, wherein the piston compressor is fastened by a plurality of tie rods (12), elongating in parallel with the vessel axis.

9. The piston compressor as claimed in any one of the preceding claims, wherein the vessel is wound with wire inducing a pre-stress such that the vessel is radially pre-stressed during operation of the piston compressor.

10. The piston compressor as claimed in any one of the preceding claims, wherein the vessel is enclosed by a force-absorbing press frame.

1 1 . The piston compressor as claimed in claim 10, wherein the force-absorbing press frame is wound with wire inducing a pre-stress such that the vessel is axially pre-stressed during operation of the piston compressor.

12. The piston compressor as claimed in any one of the preceding claims, wherein the vessel is cooled by cooling bars (10, 25) provided adjacent the vessel.

13. A compressor arrangement for compressing gas, comprising piston compressor as claimed in any one of the preceding claims.

Description:
GAS COMPRESSOR FIELD OF THE INVENTION

The present invention relates to a piston compressor for the

compression of gas.

BACKGROUND OF THE INVENTION

Compressed gas is used as a medium in a diversity of technical fields wherein examples of devices, processes and operations using compressed gas may be refrigerators, densification of powdered or cast materials in high- pressure presses, and oil service operations. Among various known techniques for compression of gas, piston compressors constitute a specific example of compression devices. Piston compressors for small to

intermediate pressures are commonly seen in automotive applications, whereas larger piston compressors are commonly found in large industrial and petroleum applications. Hydraulic drive piston compressors are often arranged such that a center piston is provided in a hydraulic cylinder. The piston divides the cylinder into two sub-spaces of the cylinder into which two sub-spaces oil is pumped periodically such that the pressure from the oil forces the center piston to reciprocate back and forth in the cylinder. The center piston is connected to a rod which extends axially with the cylinder and extends into a first and a second stage gas compression cylinder, between which cylinders the hydraulic cylinder is provided.

In a first stage gas compression cylinder, the rod extending from the hydraulic cylinder is provided with a piston arranged to compress gas entering into the compression cylinder. The compressed gas may thereafter be lead from the first stage to the second stage compression cylinder, in which a piston connected to the rod may compress the gas further in a substantially analogue way as in the first stage. The second stage gas compression cylinder, and analogously, also its piston, have a smaller diameter than the first compression cylinder and piston, such that the pressure is further augmented.

By the arrangement of the reciprocating rod and the pistons in the hydraulic drive piston compressor, the compression of gas in the first stage gas compression cylinder is performed simultaneously as the intake of gas in the second stage gas compression cylinder, when the pistons move in one direction. When the pistons move in the opposite direction, the reverse occurs. Thus, gas may initially enter the inlet of the first stage gas

compression cylinder of the hydraulic drive piston compressors, to finally exit the outlet of the second stage gas compression cylinder. Compressors of this type are utilized for the purpose to increase the pressure of gas from a given initial pressure to pressures of 100 MPa or more.

The inlet and the outlet of the first and the second stage gas

compression cylinder are controlled by valves. At intake of gas into the cylinder, i.e. at the turning point of the piston within the cylinder, the inlet valve is opened and the outlet valve is closed. At the other turning point of the piston, when the cylinder is filled with gas, the inlet is closed, while the outlet remains closed. The gas is then compressed by the piston, and at the turning point of the piston, the outlet valve is opened through which the compressed gas is led, and the cycle is thereafter repeated. As the pressure of the gas is greatly increased in the hydraulic drive piston compressor, there are high demands on the different parts and components of the compressor relating to wear and fatigue. The valves must be tight even at very high pressures.

Furthermore, at the inlets to the compression cylinder and the outlets from the compression cylinder, the piston compressor material is especially exposed to the effect of the pressure from the gas.

In some hydraulic drive piston compressors known in the art, the valves are provided at the ends of the first and second stage gas

compression cylinders, perpendicular to the axis of the rod, such that the inlet and the outlets between the valves and the cylinder space are provided perpendicular to the axis of the rod. However, there are problems related to these piston compressors. As the gas exerts a very high pressure on the cylinder material, especially in the second stage gas compression cylinder, the perpendicular bend of the gas at the inlet and the outlets results in a detrimental exposure of the cylinder material. The inlet and the outlet are critical points and may by this arrangement be responsible for material damage such as e.g. cracks or fractures in the piston compressor.

In patent application EP0064481 , a reciprocating, hydraulically operated, positive displacement compressor is disclosed. Instead of the valves being provided along an axis perpendicular to the axis of the compressor rod, the valves are provided along the compressor rod axis. However, the arrangement of the inlet and the outlet as disclosed may lead to a deteriorated efficiency of the compressor.

SUMMARY OF THE INVENTION It is an object of the present invention to mitigate at least some of the above problems and to provide an improved piston compressor. Another object of the present invention is to provide an improved compressor valve arrangement.

This and other objects are achieved by providing a piston compressor having the features defined in the independent claim. Preferred embodiments are defined in the dependent claims.

According to an aspect of the present invention, there is provided a high-pressure piston compressor for compressing gas, comprising a vessel having a vessel chamber wherein a piston is guided reciprocally, for compressing a gas in the vessel chamber during operation of the piston compressor. The high-pressure piston compressor further comprises an inlet valve housing comprising an inlet valve for controlling a supply of gas into the vessel chamber, and an outlet valve housing comprising an outlet valve for controlling a discharge of gas out from the vessel chamber. The inlet valve housing and the outlet valve housing are mounted within a portion of the vessel chamber wall, and the portion of the vessel chamber wall encloses the inlet valve housing and the outlet valve housing, such that the portion of the vessel chamber wall generates an isostatic counter-pressure on the inlet valve housing and the outlet valve housing in response to the pressure on the inlet valve housing and the outlet valve housing from the gas in the vessel chamber during operation of the piston compressor.

Thus, the piston compressor of the present invention is based on the idea of providing an improved arrangement of the inlet and outlet valve housings of the piston compressor. This is realized by providing a portion of the vessel chamber wall which encloses the inlet valve housing and the outlet valve housing. By this, the pressure on the inlet valve housing and the outlet valve housing from the gas in the vessel chamber is counteracted by the portion of the vessel chamber wall, which generates an isostatic counter- pressure on the inlet valve housing and the outlet valve housing.

The isostatic counter-pressure provides inter alia the advantage that the service life of the valves may be increased. This is due to the fact that an anisostatic pressure exerted on the valve housings may lead to detrimental stresses on the valves, which is avoided in the present invention. Thus, the present invention discloses an improvement of a piston compressor compared to other piston compressors known in the art. Consequently, several obstacles may be circumvented such as e.g. a disrupted valve operation due to wear and/or a reduced service life of the valves.

The high-pressure piston compressor for compressing gas may be a first stage piston compressor, in which vessel chamber gas is compressed during operation. Alternatively, the piston compressor referred to may be a second stage piston compressor, comprising a first and a second vessel chamber. During operation in a second stage piston compressor, gas in the first vessel chamber is compressed to a first pressure, and then lead from the first vessel chamber to the second vessel chamber, wherein the gas is further compressed to a second pressure, higher than the first pressure. As both first and second stage piston compressors are known to a man skilled in the art, further details regarding their respective functions are omitted.

In the context of the present invention, the term "valve housing" refers to the housing, cover, or casing of the valve, i.e. a protection of the valve and its function. The inlet valve controls a supply of gas into the vessel chamber of the piston compressor. In other words, the valve may be open such that gas is supplied into the vessel chamber, or analogously, it may be closed such that no gas is supplied into the vessel chamber. Furthermore, the outlet valve controls a discharge of gas out from the vessel chamber of the piston compressor. In other words, the valve may be open such that gas is discharged out from the vessel chamber, or analogously, it may be closed such that no gas is discharged out from the vessel chamber. The inlet and the outlet valves may be any kind of valves provided in devices for the purposes of gas compression, or the like, such that the inlet and outlet valves are fluid- tight when the valves are closed. For example, the inlet and outlet valves may be spring-loaded check valves, wherein the pressure of the gas actuates the opening and closing of the valves. Alternatively, an electronic control of the inlet and outlet valves is a further possible embodiment, wherein the valves may be opened or closed electronically. The function of the inlet and the outlet valves as discussed above, is known to the persons skilled in the art, and further details regarding their respective functions and/or control are therefore omitted.

Furthermore, the inlet valve housing and the outlet valve housing of the piston compressor are mounted within a portion of the vessel chamber wall. The vessel chamber wall defines the vessel chamber, and hence, the inlet and outlet valve housings are mounted within a portion of the vessel chamber wall at least partially defining the vessel chamber. By the term "mounted", it is in the context of the present invention meant that the inlet and outlet valve housings are e.g. provided, positioned or arranged within the portion of the vessel chamber.

Furthermore, the portion of the vessel chamber wall encloses the inlet valve housing and the outlet valve housing. In the context of the present invention, it is meant that the portion of the vessel chamber wall tightly encloses the inlet and outlet valve housings such that there is a close and tight fit between the portion of the vessel chamber wall and the inlet and outlet valve housings. Furthermore, by the term "enclose", it is in the context of the present invention meant that the inlet and outlet valve housings are enclosed, whereas the inlet and outlet valves, as comprised in the inlet and outlet valve housings, respectively, are not enclosed by the portion of the vessel chamber wall. For example, the material of the portion of the vessel chamber wall may surround the inlet and outlet valve housings, however not enclosing the inlet and outlet valves, such that the valves may control a supply and discharge of gas into and out from the vessel chamber, respectively.

The inlet valve housing and the outlet valve housing are mounted within a portion of the vessel chamber wall, and the portion of the vessel chamber wall tightly encloses the inlet valve housing and the outlet valve housing, such that the portion of the vessel chamber wall generates an isostatic counter-pressure on the inlet valve housing and the outlet valve housing in response to the pressure on the inlet valve housing and the outlet valve housing from the gas in the vessel chamber during operation of the piston compressor. Hence, when the gas in the vessel chamber exerts a pressure of the inlet and outlet valve housings during operation, an isostatic counter-pressure is generated from the portion of the vessel chamber wall on the inlet and outlet valve housings. Here, the inlet valve and the outlet valve housings are subjected to an isostatic pressure during operation of the piston compressor, i.e. the pressure on the inlet and outlet valve housings is evenly distributed on the inlet and outlet valve housings from the portion of the vessel chamber wall.

The isostatic counter-pressure generated by the portion of the vessel chamber wall has the advantage that it mitigates stresses on the inlet and outlet valve housings which otherwise may arise if the pressure is anisostatic. Anisostatic pressure may deform and/or damage the valve housings such that the functionality of the valves become impeded, deteriorated, or possibly, that the anisostatic pressure results in a valve break. For example, if pressure differences arise in the pressure exerted on the inlet and outlet valve housings during piston compressor operation, the valves may experience a deteriorated functionality, or possibly break, as a consequence of the resulting stress, tearing the valves. The portion of the vessel chamber wall mitigates the occurrence of damaged valves and/or worsened valve

functionality, and thereby provides an improved valve operation in the piston compressor. In other words, the isostatic counter-pressure from the portion of the vessel chamber wall on the inlet and outlet valve housings improves the service life of the valves, as valve housings subjected to isostatic pressures are less susceptible to failure compared to valve housings subjected to anisostatic pressures. As a consequence, the present invention provides a piston compressor which is more reliable in terms of operation, and thereby more economically advantageous, compared to other arrangements in the prior art.

According to an embodiment of the present invention, the piston compressor may further comprise an inlet duct mounted at least partially within the portion of the vessel chamber wall for allowing a supply of gas into the vessel chamber, wherein the inlet valve is positioned within the inlet duct and positioned immediately adjacent the vessel chamber. Alternatively, the inlet duct may instead be a pipe, a channel, a conduit, or the like, for allowing a supply of gas into the vessel chamber.

By the term "immediately adjacent", it is in this context meant that the inlet valve housing, positioned within the inlet duct, is positioned in a close vicinity of the vessel chamber. In other words, in one example, the inlet valve housing is positioned at the orifice of the inlet duct to the vessel chamber, i.e. the inlet valve housing is provided at the end of the inlet duct such that the flow of gas from the inlet duct passes the inlet valve before being supplied to the vessel chamber. For example, the space between the inlet valve and the vessel chamber may be 10-15 mm. In another example, the space between the outlet valve and the vessel chamber may also be 10-15 mm.

An advantage of the inlet valve housing being positioned immediately adjacent the vessel chamber is that the dead space of the piston compressor is decreased upon the subsequent compression of the gas when the inlet valve is closed. In other words, when the inlet valve is closed upon

compression of the gas in the vessel chamber, the gas in the vessel chamber is separated from the inlet duct. Hence, the inlet duct is sealed from the vessel chamber by the inlet valve, when the inlet valve is closed. The inlet valve housing being positioned immediately adjacent the vessel chamber in the piston compressor is advantageous regarding the compressor efficiency. During operation of the piston compressor, the piston reciprocates within the vessel chamber such that gas to be compressed is supplied to the vessel chamber when the piston expands the cylinder space, and that the gas is compressed when the piston moves in the opposite direction. Upon

compression of the gas, the inlet valve is closed such that the gas to be compressed is contained in the vessel chamber. As the arrangement of the inlet valve minimizes the dead space of the vessel chamber, inter alia the inlet duct into which gas to be compressed could leak, the efficiency of the piston compressor is increased. In other words, the positioning of the inlet valve provides an increased portion of compressed gas during operation of the piston compressor compared to other piston compressors known in the art, wherein dead spaces such as inlet ducts or the like may yield a deteriorated piston compressor efficiency.

According to an embodiment of the present invention, the inlet duct may elongate to the vessel chamber substantially in parallel with the vessel axis. This is advantageous with regard to the mitigation of wear of the piston compressor. As the gas in the piston compressor is highly compressed during operation, the flow of the gas from the inlet duct to the vessel chamber may be detrimental to the piston compressor parts subjected to the highly compressed gas. This may especially be realized when the flow of the gas is bent, i.e. that the direction of the flow at the inlet duct is changed. For example, prior art discloses arrangements wherein inlets and/or outlets are provided perpendicular to the axis of the vessel chamber. In such

arrangements, the flow of gas to and/or from the vessel chamber may be substantially vertical, whereas the flow within the vessel chamber may be substantially horizontal. For example, the direction of the flow of gas from the inlet to the vessel chamber in the prior art may be substantially 90°. In this way, the construction of the piston compressor adjacent these "bends" of the flow may be subjected to high stress. This, in turn, may yield damages such as e.g. fractures and/or cracks of the piston compressor, possibly leading to an efficiency reduction, dysfunctions, or even a breakdown of the piston compressor. The arrangement of the inlet duct of the present invention mitigates the wear of the portions of the piston compressor, subjected to the compressed gas. The inlet duct, elongated to the vessel chamber substantially in parallel with the vessel axis, eliminates any sharp bends of the flow of compressed gas. This mitigates the potentially detrimental effects of the compressed gas upon the portions of the piston compressor subjected to the compressed gas, which in turn prolongs the service life of the piston compressor.

According to an embodiment of the present invention, the piston compressor may further comprise an outlet duct mounted at least partially within the portion of the vessel chamber wall for allowing a discharge of gas out from the vessel chamber, wherein the outlet valve housing is positioned within the outlet duct and positioned immediately adjacent the vessel chamber. Alternatively, the outlet duct may instead be a pipe, a channel, a conduit, or the like, for allowing a discharge of gas from the vessel chamber.

Analogously with the advantage of the positioning of the inlet valve housing, an advantage of the outlet valve housing being positioned

immediately adjacent the vessel chamber is that the dead space of the piston compressor is decreased upon the subsequent compression of the gas when the outlet valve is closed. In other words, when the outlet valve is closed upon compression of the gas in the vessel chamber, the gas in the vessel chamber is separated from the outlet duct. Hence, the outlet duct is sealed from the vessel chamber by the outlet valve, when the outlet valve is closed.

Analogously with the positioning of the inlet valve housing, the outlet valve housing being positioned immediately adjacent the vessel chamber in the piston compressor is advantageous regarding the compressor efficiency. Upon compression of the gas, the outlet valve is closed such that the gas to be compressed is contained in the vessel chamber. As the arrangement of the outlet valve minimizes the dead space of the vessel chamber, inter alia the outlet duct into which gas to be compressed could leak, the efficiency of the piston compressor is increased. In other words, the positioning of the outlet valve provides an increased portion compressed gas during operation of the piston compressor compared to other piston compressors known in the art, wherein dead spaces such as outlet ducts or the like may yield a deteriorated piston compressor efficiency.

According to an embodiment of the present invention, the outlet duct may elongate from the vessel chamber substantially in parallel with the vessel axis. This is advantageous considering the mitigation of wear of the piston compressor, as previously mentioned for the elongation of the inlet duct. The flow of the gas from the vessel chamber to the outlet duct may be detrimental to the piston compressor parts subjected to the gas, especially when the flow of the gas is bent. For example, prior art discloses arrangements wherein the direction of the flow of gas from the vessel chamber to the outlet duct may be substantially 90°, possibly subjecting the construction of the piston

compressor adjacent these "bends" to high stress. This, in turn, may yield cracks or damages of the piston compressor, possibly leading to an efficiency reduction, dysfunctions, or even a breakdown of the piston compressor. The arrangement of the outlet duct mitigates the wear of the portions of the piston compressor, subjected to the compressed gas. The outlet duct, elongating from the vessel chamber substantially in parallel with the vessel axis, avoids any sharp bends of the flow of compressed gas. This mitigates the

detrimental effects of the compressed gas upon the portions of the piston compressor subjected to the compressed gas, thereby improving the service life of the piston compressor.

According to an embodiment of the present invention, the portion of the vessel chamber wall may be a block unit, detachable from the piston compressor. By the term "block", it is here meant a portion, a section, a piece, an enclosure, or the like.

The inlet valve housing and the outlet valve housing are mounted within the block unit. Consequently, with the block unit being detachable from the piston compressor, the inlet and the outlet valve housings may be removed and replaced. This is advantageous considering maintenance work of the inlet and/or the outlet valves, if the valves need to be repaired or replaced by new valves. Thus, the detachable block unit provides an easier and more efficient valve maintenance. According to an embodiment of the present invention, the block unit may be fastened by a threaded nut, the block unit being positioned between the threaded nut and the vessel chamber. This embodiment simplifies the operation of detaching the block unit from the piston compressor, as the threaded nut may easily be unscrewed before the block unit is detached. Furthermore, the threaded nut may be unscrewed for removal of the block unit without the need of any demounting of the tie rods of the piston compressor, which even further simplifies the operation of detaching the block unit. Analogously, a re-insertion of the block unit into the piston compressor is performed by screwing on the threaded nut after inserting the block unit. Hence, the embodiment of the present invention provides an even more simplified and efficient valve maintenance, when needed.

According to an embodiment of the present invention, the force- absorbing press frame may be fastened by a plurality of tie rods, elongating in parallel with the vessel axis. For example, a plurality of tie rods may elongate symmetrically and in parallel with the vessel axis, and extend through elements, such as gables or the like, wherein the tie rods may be fastened to the gables by nuts. In this way, the elements may resist very high pressures from the gas in an axial direction, wherein the pressure is absorbed by the tie rods.

According to an embodiment of the present invention, the vessel may be wound with wire inducing a pre-stress such that the vessel is radially pre- stressed during operation of the piston compressor. By the term "radially", it is here meant that the pre-stress induced by the wire acts in the direction of the radius of the pressure vessel. An advantage with this embodiment is that the pre-stressed vessel to a much higher extent compared to other arrangements in the prior art may withstand very high pressures arising in the vessel chamber during operation of the piston compressor. As a result, the gas may be compressed even further, increasing the efficiency of the piston

compressor. Another advantage of the vessel being radially pre-stressed is that due to the increased strength of the piston compressor, the vessel may be made thinner. This has the advantage that the cooling of the vessel chamber may be improved, as any cooling of the vessel chamber through the vessel becomes more efficient with a thinner vessel wall, decreasing cooling losses. Hence, the efficiency of the piston compressor may be even further improved.

According to an embodiment of the present invention, the vessel may be enclosed by a force-absorbing press frame. By force-absorbing press frame, it is meant that the vessel is enclosed in an axial direction by a frame that absorbs the pressure in an axial direction from the compressed gas during operation of the piston compressor. As the force-absorbing press frame even further enhances the withstand of the pressure arising from the compressed gas during operation, the efficiency of the piston compressor is even further augmented.

According to an embodiment of the present invention, the force- absorbing press frame is wound with wire inducing a pre-stress such that the vessel is axially pre-stressed during operation of the piston compressor. In this embodiment, wire is wound in an axial direction of the vessel such that the vessel is pre-stressed in a direction of the vessel axis. By this, the efficiency of the piston compressor may be improved even further, absorbing the axial pressure from the gas during operation.

According to an embodiment of the present invention, the vessel is cooled by cooling bars provided adjacent the vessel. By this arrangement, a transfer of cold is provided from the cooling bars to the vessel during operation of the piston compressor. In its turn, the vessel transfers the cold to the vessel chamber, such that the gas within the vessel chamber is cooled. By cooling the gas in the vessel chamber, the temperature decrease of the gas results in a volume decrease of the gas, such that the gas may be compressed even further in the piston compressor. Thus, this has the advantage that the efficiency of the piston compressor is even further enhanced.

Further objectives of, features of, and advantages with, the present invention will become apparent when studying the following detailed disclosure, the drawings and the appended claims. Those skilled in the art will realize that different features of the present invention can be combined to create embodiments other than those described in the following. BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing a currently preferred embodiment of the invention, wherein:

Fig. 1 is a cross-section view of the piston compressor, and

Figs. 2-5 are views of an end portion of the piston compressor. DETAILED DESCRIPTION

In the following description, the present invention is described with reference to a piston compressor.

In Fig. 1 , a cross-section view of the piston compressor 1 is shown. As the piston compressor 1 is elongated in the horizontal direction, the figure is provided with partitions 2a, 2b, 2c to make the figure more compact. Thus, dimension relationships in the horizontal direction in the figure of the piston compressor 1 is to be construed with this in mind.

In the piston compressor 1 , a piston 3 is provided in a central vessel 4, into which central vessel space 5 oil is pumped periodically to either side of the piston 3 such that the pressure from the oil forces the piston 3 to reciprocate back and forth in the central vessel space 5.

Along the axial direction of the central vessel 4 is provided a first inner gable 6 and a second inner gable 7, defining the central vessel space 5 in the axial direction of the central vessel 4.

The piston 3 extends axially with the central vessel 4 and extends into a first stage gas compression vessel chamber, hereon denoted as the first vessel chamber 8. The first vessel chamber 8 is elongated in the horizontal direction.

In a radial direction, the first vessel chamber 8 is enclosed by a first vessel 9, the first vessel chamber 8 and the first vessel 9 having a common central axis. A plurality of cooling bars 10 are provided adjacent the first vessel 9, in the axial direction of the first vessel 9. A cooling medium, such as water, may be guided through the plurality of cooling bars 10 such that the first vessel 9 is cooled during operation of the piston compressor 1 .

In its turn, the cooled first vessel 9 transfers cold to the first vessel chamber 8, such to cool the gas provided in the first vessel chamber 8. The cooling bars 10 may be provided tightly on the first vessel 9 for an efficient cooling of the first vessel chamber 8.

A first outer gable 1 1 is provided adjacent the first vessel 9, such that the first vessel 9 is provided between the first inner gable 6 and the first outer gable 1 1 . A plurality of tie rods 12 are provided through the first inner gable 6, extending parallelly to the first vessel 9, and extending through the first outer gable 1 1 . The plurality of tie rods 12 are fastened to the first outer gable 1 1 by nuts 13. The first outer gable 1 1 at least partially encloses a first portion of the vessel chamber wall 14, hereafter referred to as the first block 14. In Fig. 1 , the first block 14 penetrates the first outer gable 1 1 and elongates into the first vessel chamber 8. Within the first block 14 is provided a first inlet valve housing 17 comprising a first inlet valve 18, and a first outlet valve housing 15 comprising a first outlet valve 16. The first block 14 tightly encloses the first inlet valve housing 17 and the first outlet valve housing 15, mounted within the first block 14. By this, the first block 14 generates an isostatic counter- pressure on the first inlet valve housing 17 and the first outlet valve housing 15 in response to the pressure on the first inlet valve housing 17 and the first outlet valve housing 15 from the gas in the first vessel chamber 8 during operation of the piston compressor 1 .

Furthermore, during operation of the piston compressor 1 , the first inlet valve 18 controls the supply of gas into the first vessel chamber 8, whereas the first outlet valve 16 controls the discharge of gas from the first vessel chamber 8.

A first inlet duct 20 is provided at least partially within the first block 14, extending parallelly to the axis of the first vessel 9. During operation of the piston compressor 1 , gas is supplied into the first vessel chamber 8, through the first inlet duct 20, and through the first inlet valve 18.

Analogously, at least partially within the first block 14 is provided a first outlet duct 19, extending parallelly to the axis of the first vessel 9. During operation of the piston compressor 1 , gas is discharged from the first vessel chamber 8, through the first outlet valve 16, and into the first outlet duct 19.

Hence, the first inlet valve 18 is provided between the first inlet duct 20 and the first vessel chamber 8 such that upon operation of the piston compressor 1 , gas may enter the first vessel chamber 8 first through the first inlet duct 20, and then through the first inlet valve 18, when the inlet valve is open. In other words, the first inlet valve 18 is provided on the downstream side of the first inlet duct 20.

Furthermore, the first inlet valve 18 is provided at the end of the first inlet duct 20, in terms of direction of the flow of the gas. In other words, the first inlet valve 18 is provided immediately adjacent the first vessel chamber 8. Thus, "dead space" of the piston compressor 1 is decreased upon the subsequent compression of the gas when the first inlet valve 18 is closed. In other words, when the first inlet valve 18 is closed upon compression of the gas, the gas in the first vessel chamber 8 is separated from the first inlet duct 20, as the first inlet valve 18 is positioned at the downstream end of the first inlet duct 20.

Analogously, the first outlet valve 16 is provided between the first outlet duct 19 and the first vessel chamber 8 such that upon operation of the piston compressor 1 , gas may exit the first vessel chamber 8 first through the first outlet valve 16, and then through the first outlet duct 19, when the first outlet valve 16 is open. In other words, the first outlet valve 16 is provided on the upstream side of the first outlet duct 19.

The first outlet valve 16 is provided at the beginning of the first outlet duct 19, in terms of direction of the flow of the gas. In other words, the first outlet valve 16 is provided immediately adjacent the first vessel chamber 8. Thus, "dead space" of the piston compressor 1 is decreased upon the subsequent compression of the gas when the first outlet valve 16 is closed. In other words, when the first outlet valve 16 is closed upon compression of the gas, the gas in the first vessel chamber 8 is separated from the first outlet duct 19, as the first outlet valve 16 is positioned at the upstream end of the first outlet duct 19. The first block 14 is fastened by a threaded nut 21 , the first block 14 being positioned between the threaded nut 21 and the first vessel chamber 8.

The first vessel 9 is wound with wire in a radial direction of the first vessel chamber 8. By this, the first vessel chamber 8 is radially pre-stressed during operation of the piston compressor 1 . In Fig. 1 , a portion of the first block 14 is subjected to the pre-stress of the wire, whereas the first inlet valve housing 17, the first inlet valve 18, the first outlet valve housing 15, and the first outlet valve 16 are subjected to the pre-stress of the wire.

After compression of the gas in the first vessel chamber 8, i.e. after the gas compression in the first stage of the piston compressor, the first outlet valve 16 is opened. The compressed gas may thereafter be lead in a duct from the first vessel chamber 8 to a second vessel chamber 23 of the piston compressor 1 , for further compression of the gas in a second stage. It will be appreciated that the volume of the second vessel chamber 23 in Fig. 1 is greatly reduced as the piston 3 is in its end position, and the second vessel chamber 23 is therefore indicated with a dashed line.

As functionalities and features of the piston compressor in the second stage have similarities with functionalities and features already described for the first stage, a more concise description is presented for the second stage in the following, and reference may be made to the description of the first stage.

Analogously to the operation of the piston compressor 1 in the first vessel chamber 8 of the first stage, the piston 3 reciprocates back and forth within a second vessel chamber 23. However, the second vessel chamber 23 has a smaller diameter than the first vessel chamber 8, such that the pressure of the gas is further increased during operation of the piston compressor 1 . The second vessel chamber 23 is enclosed by a second vessel 24, the second vessel chamber 23 and the second vessel 24 having a common central axis. A plurality of cooling bars 25, extending axially with the second vessel chamber 23, are provided tightly around the second vessel 24 such that the second vessel chamber 23 is cooled during operation of the piston compressor 1 . A second outer gable 26 is provided adjacent the second vessel 24. The plurality of tie rods 12, provided through the first outer gable 1 1 , extend parallelly to the first vessel 9, and extend through the first inner gable 6, the second inner gable 7, and the second outer gable 26. The plurality of tie rods 12 are fastened to the second outer gable 26 by nuts 27. The second outer gable 26 at least partially encloses a second portion of the vessel chamber wall 28, hereafter referred to as the second block 28. The second block 28 penetrates the second outer gable 26 in the shape of a wedge or a cone, decreasing its circumference in the direction from the second outer gable 26 towards the second vessel chamber 23. As the diameter of the second vessel chamber 23 is less than that of the first vessel chamber 8, the wedge or cone shape of the second block 28 is more pointed or sharp compared to the shape of the first block 14.

Within the second block 28 is provided a second inlet valve housing 29 comprising a second inlet valve 30, and a second outlet valve housing 31 comprising a second outlet valve 32. The second block 28 tightly encloses the second inlet valve housing 29 and the second outlet valve housing 31 , mounted within the second block 28. By this, the second block 28 generates an isostatic counter-pressure on the second inlet valve housing 29 and the second outlet valve housing 31 in response to the pressure on the second inlet valve housing 29 and the second outlet valve housing 31 from the gas in the second vessel chamber 23 during operation of the piston compressor 1 .

During operation of the piston compressor 1 , the second inlet valve 30 controls the supply of gas into the second vessel chamber 23, whereas the second outlet valve 32 controls the discharge of gas from the second vessel chamber 23.

At least partially within the second block 28 is provided a second inlet duct 33, the second inlet duct 33 being slightly inclined in relation to the axis of the second vessel 24. The slight inclination is due to the decreased diameter of the second vessel chamber 23 compared to the first vessel chamber 8, such that the second inlet duct 33 may more easily fit within the second block 28. During operation of the piston compressor 1 , gas is supplied via the second inlet duct 33, through the second inlet valve 30, and into the second vessel chamber 23.

The second inlet valve 30 is provided at the end of the second inlet duct 33, in terms of direction of the flow of the gas. In other words, the second inlet valve 30 is provided immediately adjacent the second vessel chamber 23. Thus, "dead space" of the piston compressor 1 is decreased upon the subsequent compression of the gas when the second inlet valve 30 is closed. In other words, when the second inlet valve 30 is closed upon compression of the gas, the gas in the second vessel chamber 23 is separated from the second inlet duct 33, as the second inlet valve 30 is positioned at the downstream end of the second inlet duct 33.

Analogously, a second outlet duct 34 is provided at least partially within the second block 28. The second outlet duct 34 is slightly inclined in relation to the axis of the first vessel 9 and forms a v-shape together with the second inlet duct 33. During operation of the piston compressor 1 , gas is discharged from the second vessel chamber 23, through the second outlet valve 32, and through the second outlet duct 34.

The second outlet valve 32 is provided at the beginning of the second outlet duct 34, in terms of direction of the flow of the gas. In other words, the second outlet valve 32 is provided immediately adjacent the second vessel chamber 23. Thus, "dead space" of the piston compressor 1 is decreased upon the subsequent compression of the gas when the second outlet valve 32 is closed. In other words, when the second outlet valve 32 is closed upon compression of the gas, the gas in the second vessel chamber 23 is separated from the second outlet duct 34, as the second outlet valve 32 is positioned at the upstream end of the second outlet duct 34.

In Fig. 2, the rightmost portion of the piston compressor 1 is shown, comprising the second stage gas compression.

The second outer gable 26 is provided adjacent a winding gas cylinder 35, around which wire is wound for yielding a pre-stress. The plurality of tie rods 12, wherein only two are shown in this figure for an enhanced clarity, extend parallelly to the winding gas cylinder 35, and extend through the second outer gable 26. The plurality of tie rods 12 are fastened to the second outer gable 26 by nuts 27. In the extension of the second inlet duct 33 and the second outlet duct 34, a collet 36 is provided for each duct.

Fig. 3 shows the portion of the piston compressor 1 as shown in Fig. 2, but wherein the winding gas cylinder 35 has been removed. The plurality of cooling bars 25, are provided tightly around the second vessel 24 such that the second vessel chamber 23 is cooled during operation of the piston compressor 1 .

Fig. 4 shows the portion of the piston compressor 1 as shown in Fig. 3, but wherein the plurality of cooling bars 25 and the second outer gable 26 have been removed. The figure reveals the second vessel 24 and the second block 28.

Fig. 5 shows the portion of the piston compressor 1 as shown in Fig. 4, but wherein the second vessel 24 and the second block 28 have been removed. The figure shows the positioning of the second inlet valve 30 and the second outlet valve 32.

Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. The described embodiments are therefore not intended to limit the scope of the invention, as defined by the appended claims. For example, the

dimensions of the piston compressor 1 may be construed broadly, as the piston compressor 1 could e.g. be longer or shorter, thicker or thinner than that depicted and described. These dimensional aspects also holds for any component comprised in the piston compressor 1 .

Moreover, although a two stage gas compressor has been described, the concept of the present invention may instead be implemented within a first stage gas compressor.

Furthermore, the number of components in the piston compressor 1 may differ from those described. For example, the number of the plurality of tie rods 12, cooling bars 10 and 25, and/or gables 6 and 7, may vary.

All references to "a/an/the [element, device, component, means, step, etc]" are to be interpreted openly as referring to at least one instance of said element, device, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.