Title:
RECIPROCATING COMPRESSOR
Kind Code:
A1


Abstract:
A reciprocating compressor includes a suction port, through which a working gas is taken into a cylinder volume, which is closed and opened by a suction valve, and a discharge port, through which the working gas compressed by a reciprocating piston is emitted toward an end use, which is closed and opened by a discharge valve, wherein the maximum discharge pressure determined by a compression ratio which is calculated by the ratio of the cylinder volume in a case where the piston is located at the bottom dead center position and the cylinder volume in a case where the piston is located at the top dead center position, is set so as to be compatible with the demand pressure of said gas end use.



Inventors:
Inoue, Hiroshi (Yokohama-city, JP)
Application Number:
11/862344
Publication Date:
04/03/2008
Filing Date:
09/27/2007
Assignee:
ANEST IWATA CORPORATION (Yokohama-shi, JP)
Primary Class:
Other Classes:
417/437
International Classes:
F04B39/10; F04B19/22; F04B53/12
View Patent Images:
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Primary Examiner:
COMLEY, ALEXANDER BRYANT
Attorney, Agent or Firm:
Rossi, Kimms & McDowell LLP (Ashburn, VA, US)
Claims:
What is claimed is:

1. A reciprocating compressor comprising; a suction port, through which a working gas is taken into a cylinder, wherein the suction port is opened/closed by a suction valve; a discharge port, through which the working gas compressed by a reciprocating piston is emitted toward an end use, wherein the discharge port is opened/closed by a discharge valve; and a cylinder volume setting mechanism that determines a cylinder volume of the cylinder; wherein a maximum discharge pressure determined by a compression ratio, which is calculated by the ratio of the cylinder volume in a case where the reciprocating piston is located at the bottom dead center position of the cylinder and the cylinder volume in a case where the reciprocating piston is located at the top dead center position of the cylinder, is set by the cylinder volume setting mechanism so as to be compatible with the demand pressure of the gas end use.

2. The reciprocating compressor of claim 1, further comprising a cylinder-cover which puts the lid on said cylinder, wherein the cylinder-cover is of a boxy type, and wherein within the cylinder cover a suction chamber is connected to said suction port and is juxtaposed with a discharge chamber connected to said discharge port.

3. A reciprocating compressor comprising; a suction port, through which a working gas is taken into a cylinder volume of a cylinder, wherein the suction port is opened/closed by a suction valve; and a discharge port, through which the working gas compressed by a reciprocating piston is emitted toward an end use, wherein the discharge port is opened/closed by a discharge valve; wherein said suction port and said suction valve are at an upper part of a suction side of a cylinder-wall of said cylinder; wherein said discharge port and said discharge valve are at the upper part of a discharge side of the cylinder-wall of said cylinder; and wherein a discharge chamber is at the above-mentioned discharge side of said cylinder-wall and is connected to said discharge port.

4. A reciprocating compressor comprising; a suction port, through which a working gas is taken into a cylinder volume of a cylinder, wherein the suction port is opened/closed by a suction valve; and a discharge port, through which the working gas compressed by a reciprocating piston within the cylinder is emitted toward an end use, wherein the discharge port is opened/closed by a discharge valve; wherein the suction port, which is opened and shut by said suction valve, is placed at a top wall of said piston that faces with said cylinder volume; wherein an inhalation passage connected to said suction port is provided inside said piston; wherein said discharge port and said discharge valve are at an upper part of a cylinder-wall of said cylinder; and wherein a discharge chamber is connected to said discharge port.

5. The reciprocating compressor of claim 1, wherein the cylinder volume setting mechanism includes: a second cylinder volume located by the upper part of a cylinder-wall of the cylinder, which is connected to the cylinder volume, and a piston that is capable of adjusting the second cylinder volume.

6. The reciprocating compressor of claim 2, wherein the cylinder volume setting mechanism comprises a spacer located between the cylinder and the cylinder-cover.

Description:

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a reciprocating compressor, including a suction port, through which a working gas is taken into a cylinder room, and which is closed and opened by a suction valve, and a discharge port, through which the working gas compressed by a reciprocating piston is fed toward an end use, and which is closed/opened by a discharge valve.

2. Description of the Related Art

There are a variety of control principles that may be used to control the pressure in a cylinder including: automatic start/stop control or pressure switch control; load/no-load control or unloader control; upper limit pressure release control or safety valve control; or a combination of these controls.

In the above cylinder internal pressure control systems, a pressure switch control device, an unloader control device or a safety valve is required, each corresponding to pressure switch control, unloader control or safety valve control, respectively. In addition, an air holder and/or a gas holder is necessary so as to maintain the operation stability of each control device.

Moreover, in a reciprocating compressor, maximum discharge pressure Pmax depends on the compression ratio κ of the piston, where κ is defined as


(Vh+Vc)/Vc

and Vh and Vc are the piston stroke volume and the cylinder dead volume respectively. Here the cylinder dead volume means the cylinder volume at a time when the piston is located at a top dead center position. When the cylinder dead volume Vc is less than the conventionally experienced value or when the compression ratio κ is more than the conventionally experienced value, the maximum discharge pressure Pmax would exceed a permissible value, thereby resulting in Pmax bringing excessive stress to the static and/or running components around the cylinder room.

In order to evade the excessive rise of the maximum discharge pressure Pmax, discharge pressure control methods have been conventionally introduced to keep the maximum discharge pressure to less than a permissible value.

For example, patent document WO 02/29251 discloses a method of controlling the maximum discharge pressure. In this related method, the maximum discharge pressure is prevented from exceeding the permissible limit by: introducing a relief port and a relief valve which opens and closes the relief port at a cylinder cover; making the relief valve opened by means of a drive projection fitted on the top of a piston at the final stage of the piston compression stroke; and draining a part of the gas in the cylinder outside through a relief port.

It is necessary that the maximum discharge pressure Pmax of the compressor be kept within a service pressure so as not to cause excessive stresses to the static and/or running components around the cylinder room and so as to conform with the specified pressure of the instrumentation that uses the discharged gas. In the related art of the aforementioned patent document WO 02/29251, the maximum discharge pressure Pmax is controlled to a target pressure so as to meet both conditions by means of the maximum discharge pressure control devices.

However, in the related method discussed above, it is required to additionally introduce special parts and/or related machining in order to control the maximum discharge pressure in a way that the relief port, the relief valve to open/close the relief port and the opening/closing mechanism of the valve are installed within the cylinder cover as well as in a way that the drive projection on the top surface of the piston is specially machined and/or manufactured. As a result, in the related method, processing man-hours to make the compressor and production costs of the compressor are inevitable increased.

SUMMARY OF THE INVENTION

The present invention is directed to realizing a reciprocating compressor capable of holding the discharge pressure of the compressor so as to prevent the components of the compressor from breakage, and is also capable of always keeping the discharge pressure of the compressor at a target pressure in order not to violate a demand service pressure determined by the end-application conditions or specified limitations of instruments used downstream of the compressor, without an increase of part marks increasing processing man-hours or increasing production costs as a result.

According to the present invention, a reciprocating compressor includes a suction port, through which a working gas is taken into a cylinder room and which is closed/opened by a suction valve, and a discharge port, through which the working gas compressed by a reciprocating piston is fed toward an end use and which is closed/opened by a discharge valve. Maximum discharge pressure is determined by a compression ratio, which is calculated by the ratio of the cylinder volume in a case where the piston is located at the bottom dead center position and the cylinder volume in a case where the piston is located at the top dead center position, and the maximum discharge pressure is set so as to be compatible with the demand pressure of the gas end use.

Specifically, the present invention provides a reciprocating compressor that includes: a cylinder-cover, which puts a lid on a cylinder and is of a boxy type, and a suction chamber connected to a suction port is juxtaposed with a discharge chamber connected to a discharge port; wherein the suction port and the suction valve are at one side of an upper part of a cylinder-wall of the cylinder, the discharge port and the discharge valve are at another side of the upper part of the cylinder-wall of the cylinder, the discharge chamber is at the discharge side of the cylinder, being connected to discharge port, and additionally the suction valve is placed so as to open/close the connection between the above-mentioned discharge port and discharge chamber; wherein the suction port, which is opened/closed by the suction valve, is placed at a top wall of the piston, the top wall facing with the above mentioned cylinder volume, an inhalation passage connected to the above-mentioned suction port is prepared inside the above-mentioned piston, the above-mentioned discharge port and the above-mentioned discharge valve are at the upper part of the cylinder-wall of the above-mentioned cylinder, the discharge chamber is at the above-mentioned discharge side of the cylinder, the chamber being connected to the above-mentioned discharge port, and that the above-mentioned suction valve is placed so as to open/close the connection between the above-mentioned discharge port and discharge chamber; and wherein, outside the upper part of the above-mentioned cylinder-wall of the above-mentioned cylinder, is prepared a second cylinder volume, which is connected to the aforementioned cylinder volume, and within which a piston is placed so as to be capable of adjusting the second cylinder volume.

According to the present invention, the maximum discharge pressure can always be held so as to be compatible with the demand pressure of the above-mentioned gas end use, without the mechanism described in the above-mentioned related art, namely, without requiring a drive projection on the top surface of the piston, a relief port and a relief valve to open/close the relief port, both of which are prepared in the cylinder cover, and an opening/closing device of the relief valve.

The present invention provides a way to thoroughly dispense with the increase in the number of parts for controlling the maximum discharge pressure of a compressor, with the increase in the number of processing man-hours for parts, as well as with the increase of production costs of the compressor which result therefrom. Also, the present invention provides a way to always keep the compressor discharge pressure at or below the target discharge pressure, enabling the compressor discharge pressure to be satisfactory compatible with the demand pressure of the gas end use and enabling compressor parts to be prevented from possible breakage.

Moreover, in case of ordinary compressors including the box type cylinder cover which puts the lid on the above-mentioned cylinder and within which the suction chamber connected to the suction port is juxtaposed with the discharge chamber connected to the discharge port, the control effectiveness, that the maximum discharge pressure of the compressors is held within the range of the demand service pressure, is obtained by means of inserting a spacer into the contact surface between the cylinder and the cylinder cover as well as by means of only adjusting the volume of the cylinder volume. The above approach is applicable to current compressors as they are.

In case of the compressors including:

    • (a) a suction port and a suction valve being located at the upper part of one side of the cylinder-wall of the cylinder;
    • (b) a discharge port and a discharge valve being located at the upper part of another side of the cylinder-wall of the cylinder; and
    • (c) a discharge chamber being located at the discharge side of said cylinder, as well as being connected to the discharge port,
      wherein the suction valve is placed so as to open/close the connection between the discharge port and the discharge chamber, it becomes possible:
    • (i) to secure room for placing the suction valve at the upper part of the cylinder-wall of the cylinder volume;
    • (ii) to allow the structure of a cylinder cover putting the lid on the cylinder to be of simple plate type instead of the complicated box type in a manner that a discharge chamber be at the discharge side of the cylinder, being connected to the discharge port.

In the above manner, the production cost of the cylinder cover can be reduced thanks to the simplification of the structure of the cylinder cover and a small compact compressor can be realized with a reduced length of the piston running direction.

Moreover, since the cylinder cover can be of a plate type and cooling fins can be easily formed on the external surface of the cylinder cover, an improved cooling-effect of the cylinder can be expected.

In case of a reciprocating compressor:

    • wherein a suction port, which is opened and shut by the suction valve, is placed at the top wall of the piston the wall facing with the cylinder volume;
    • wherein an inhalation passage connected to the suction port is prepared inside the piston;
    • wherein the discharge port and the discharge valve are at the upper part of the cylinder-wall of the cylinder; and
    • wherein a discharge chamber is at the discharge side of the cylinder, the chamber being connected to the discharge port,
      by means of
    • (1) preparing the discharge chamber connected to the discharge port at the discharge side of the cylinder, and
    • (2) placing the suction port, which is opened and shut by the suction valve, at the top wall of the piston, the wall facing with the cylinder volume; it becomes possible:
  • (a) to reduce the production cost of the cylinder cover thanks to the simplification of the structure of the cylinder cover; and
  • (b) to realize a small compact compressor with a reduced length along the piston running direction, because the discharge chamber can be removed from the cylinder cover and cylinder cover can be of simple plate type instead of the complicated box type as mentioned before.

In addition, an improved cooling-effect of the cylinder can be expected, since the cylinder cover can be of plate type and cooling fins can be easily formed on the external surface of the cylinder cover.

Moreover, since the suction port and the suction valve are placed at the top wall of the piston, the wall facing with the cylinder volume, working gas can be inhaled into the cylinder during the piston down-stroke with the valve opened by the negative pressure in the cylinder. During the piston up-stroke with the valve closed by pressure rising in the cylinder, working gas can be compressed. In this manner, the suction valve can be opened/closed by use of reciprocating motion of the piston.

Thanks to the above manner, since it becomes possible for the inhalated gas to be introduced from the lower part of the cylinder-wall of the cylinder or from the lower part of the crankcase, the degree of freedom of design gas inhalation can be increased, namely, the number of alternative selections of gas inhalation is increased.

In addition, in case of the compressors characterized in that, beside the upper part of the cylinder-wall of the cylinder, is prepared a second cylinder volume, which is connected to the aforementioned cylinder volume, and within which a piston be placed so as to be capable of adjusting the second cylinder volume, the cylinder dead volume can be redefined as the sum of the original cylinder dead volume, which is the cylinder volume at a time when the piston is at the top dead center, and the second cylinder volume. In this manner, the maximum discharge pressure can be adjusted so as to be compatible with the demand pressure of gas end use.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail with reference to the preferred embodiments of the invention and the accompanying drawings, wherein:

FIG. 1 shows a cylinder-centerline section regarding an embodiment of the reciprocating compressor of the present invention;

FIG. 2 shows a cylinder-centerline section regarding another embodiment of the upper part of the reciprocating compressor of the present invention;

FIG. 3 shows a third embodiment of the present invention corresponding to FIG. 2; and

FIG. 4 shows a fourth embodiment of the present invention corresponding to FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, the present invention will be described in detail with reference to the embodiments shown in the figures. However, the dimensions, materials, shape, the relative placement and so on of a component mentioned in these embodiments shall not be construed as limiting the scope of the invention thereto, unless especially specific mention is placed.

FIG. 1 illustrates a reciprocating compressor in accordance with a first embodiment of the present invention. A crankshaft 6 is installed in and penetrates a crankcase 1. Both ends of the crankshaft 6 are rotation-freely supported by main bearings 7. A cylinder 3 is securely fastened to the upper part of the crankcase 1 by means of plural bolts which are not illustrated in FIG. 1.

A piston 5 is fitted inside the cylinder 3 so as to be able to carry out reciprocating movement. The piston 5 connected to the small end of a connecting rod 8 via a piston pin 5a, while the large end of the connecting rod 8 is rotatably connected to the crankshaft 6 via a bearing. A crankcase cover 2 is firmly fastened to the crank-axial direction one side of the crankcase 1 by plural bolts 2a.

A valve-case 4a is positioned at the upper side of the cylinder 3 via a spacer 40. Further, a cylinder cover 4 is placed at the upper side of the valve-case 4a via a gasket not illustrated in the figure. The cylinder cover 4 and the valve-case 4a are together fixed over the top face of the cylinder 3 with plural tightening-bolts that are not illustrated in the figure.

The cylinder cover 4 is formed in the shape of box type. Within the cylinder cover 4, a suction chamber 130 is provided which is connected to a suction port 10, a discharge chamber 15 is provided which is connected to a discharge port 13, and a partition wall 130 is provided between the suction chamber and the discharge chamber. In addition, the suction chamber 130 has a inhalation hole 12 opened for gas inhalation and the discharge chamber 15 has a discharge hole 16 opened for gas discharge.

Further, the suction port 10 and the discharge port 13 are positioned at the valve-case 4a. The suction port 10 is opened/closed by means of a suction valve 11, while the discharge port 13 is opened/closed by means of a discharge valve 14.

According to the present invention in the case of production of the reciprocating compressor constituted as mentioned above, the dimension C corresponding to the cylinder volume 9 in FIG. 1 is set so that the maximum pressure in the cylinder coincides with the demand pressure of the end use of the compressed gas which is passed through the discharge chamber 15, where the maximum pressure in the cylinder is decided by the compression ratio computed with a ratio of X and Y, where X denotes the cylinder volume 9 surrounded by the top surface of piston 5 at time in the bottom dead center position (shown by B in FIG. 1), the interior of the cylinder 3, and the undersurface of the cylinder cover 4 (valve-case 4a side), and where Y denotes the cylinder volume 9 surrounded by the top surface of piston 5 at time in the top dead center position (shown by A in FIG. 1), the interior of the cylinder 3, and the undersurface of the cylinder cover 4 (valve-case 4a side).

That is, by means of changing the thickness of the spacer 40, the cylinder volume 9 is adjusted so that the pressure of the cylinder volume 9, in time when the piston 5 comes to a top dead center A, coincides with the demand pressure of the end use of the compressed gas. In addition, the length S shows a stroke of piston 5.

In operation, the rotational drive of the crankshaft 6 is carried out by drive sources, such as a motor (not shown), and the rotary motion of the crankshaft 6 is changed into the reciprocating motion of the piston 5 through the connecting rod 8.

Gas is introduced into the cylinder 3 with the suction valve opened during the down stroke of the piston 5 from the top dead center A to the bottom dead center B. The gas in the cylinder 3 is then compressed with the up stroke of the piston 5 from the bottom dead center B to the top dead center A. The compressed gas is then fed into the use end through a discharge hole 16 after the pressure pulsation is relaxed in the discharge chamber 15.

The arrows show the flow of gas in FIG. 1, as described above (the same is said of FIGS. 2-4).

Since, in the case of production of the reciprocating compressor, the cylinder volume 9 is set so that the maximum pressure in the cylinder, which is decided by the compression ratio, coincides with the demand pressure of the end use equipment of the discharged compressed-gas, the maximum pressure in the cylinder at the top dead center A of the piston 5 does not exceed the demand pressure (necessary working-pressure) of the end use and the maximum pressure in the cylinder does not rise abnormally during operation.

The above mentioned first embodiment requires the compressor to be assembled only in the manner that the cylinder volume 9 is set so that the maximum pressure in the cylinder, which is decided by the compression ratio, coincides with the demand pressure for the end use equipment of the discharged compressed-gas. Accordingly, the first embodiment gives a way to completely dispenses with the mechanism of the related art, for controlling the maximum discharge pressure of the compressor toward a target pressure, such as a drive projection on the top surface of the piston, a relief port and a relief valve to open/close the relief port both of which are prepared in the cylinder cover and an opening/closing device of the relief valve. Namely, the first embodiment enables the maximum discharge pressure to hold so as to be compatible with the demand pressure of the above-mentioned gas end use completely without the mechanism such as described in aforementioned patent document.

Consequently, the first embodiment makes it possible to realize a reciprocating compressor that is capable of holding the discharge pressure of the compressor so as to prevent the components of the compressor from breakage, and that is capable of keeping always the discharge pressure of the compressor at the target pressure in order not to violate the demand service pressure determined by the end-application conditions or specified limitations of instruments used downstream of the compressor, without an increase of part marks, processing man-hours and production costs.

Moreover, in case of an ordinary compressor comprising the box type cylinder cover 4 which puts the lid on said cylinder 3 and within which the suction chamber 130 connected to the suction port 10 is juxtaposed with the discharge chamber 15 connected to the discharge port 13, the control effectiveness, that the maximum discharge pressure of the compressors is held within the range of the demand service pressure, is obtained by means of inserting a spacer 40 into the contact surface between the cylinder and the cylinder cover as well as by means of only adjusting the volume of the cylinder volume. This embodiment is applicable to current compressors as they are.

FIG. 2 illustrates a partial section view of the upper part along the cylinder centerline 100 of the reciprocating compressor concerning the second embodiment of the present invention.

In this second embodiment, horizontally by one side at the upper part of the cylinder-wall of the cylinder 3, are prepared a suction port 20 and a suction valve 11 which opens/closes the suction port 20. By another side (opposite side of the suction port 20) at the upper part of the cylinder-wall, are prepared a discharge port 23 and a discharge valve 14 which opens/closes the discharge port 23.

Furthermore, by the discharge-side at the upper part of the cylinder 4, is prepared a discharge chamber 24 connected to the discharge port 23. Here, discharge valve 14 is placed so as to open/close the connection between the discharge port 23 and discharge chamber 24.

Here, a plate type cylinder cover 21 puts the lid on the upper part opening of the cylinder 3 as well as the upper part opening of the discharge chamber 24.

The other constitution of the second embodiment is the same as that of the above first embodiment and the same part number is used also in the FIG. 2.

The second embodiment as stated above enables a large height of the cylinder volume 9. Accordingly, the second embodiment also secures the space for installing the suction valve 11 at the upper part of the cylinder-wall. Further, the second embodiment enables the cylinder cover 21 which puts the lid on the cylinder 3 to be of plate type by means of placing, at the discharge side of the cylinder 3, the discharge chamber 24 connected to the discharge port 23, while removing discharge chamber from the cylinder cover 21 and making the cylinder cover 21 only put the lid on the cylinder 3 and the discharge chamber 24.

In the manner as mentioned above, while the structure of the cylinder cover 21 becomes simple, the production cost of the cylinder cover 21 can be reduced and a small compact structure can be realized with restrained length along the cylinder center line.

Moreover, since the cylinder cover 21 can be of plate type, it becomes easier to form cooling fins (not shown) on the external surface of the cylinder cover 21, and an improved cooling effect of the cylinder 3 can be expected.

FIG. 3, corresponding to FIG. 2, shows the third embodiment of the present invention.

In the third embodiment, on the outside surface of the upper part of the cylinder-wall of the cylinder, are placed the discharge port 23 and the discharge valve 14 which opens/closes the discharge port 23, in the same manner as in the second embodiment. As to the discharge side constitution, there is a piston suction hole 25 at the upper part of the piston 5 of which the upper part faces the above-mentioned cylinder volume 9. The piston suction hole 25 is opened/closed by a suction valve 11.

In this third embodiment, the suction entrance (not shown) of the gas is prepared at the lower part of the cylinder-wall of the cylinder 3 or at the side face wall of the crankcase 1. During the down stroke of the piston 5, the suction valve 11 is opened with the aid of the negative pressure in the cylinder 3, while, during the up stroke of the piston 5, the suction valve 11 is closed with the aid of the pressure increase in the cylinder 3 and the gas is compressed.

In addition, as in the above-described second embodiment, the plate type cylinder cover 21 puts the lid on the upper part opening of the cylinder 3 and the upper part opening of the discharge chamber 24.

The other construction is the same as that of the above first embodiment, and the same part as that of the above first embodiment is quoted with the same reference number.

In case of this third embodiment, while the discharge chamber 24 which is connected to the discharge port 23 is prepared at the discharge side of the cylinder 3, the piston suction hole 25 is opened at the upper part of the piston 5 of which the upper part faces the cylinder volume 9, the hole 25 being opened/closed by the suction valve 11. Accordingly, as in the case of the second embodiment, the cylinder cover 21 could be of plate type and of simple structure, while having the function of only putting the lid on the cylinder 3 and the discharge chamber 24. As a result, the production cost of the cylinder cover 21 can be reduced and a small compact structure of the cylinder cover can be realized, the structure bringing restrained length of the compressor along the cylinder-center-line.

Moreover, it would be easy to form cooling fins on the external surface of the cylinder cover 21, and improved cooling effect of the cylinder can therefore be expected.

Moreover, since the piston suction hole 25 and the suction valve 11 are placed at the top wall of the piston 5, the wall facing with the cylinder volume 9, gas can be inhaled into the cylinder 3 during the piston 5 down-stroke with the suction valve 11 opened with the aid of the negative pressure in the cylinder 3. During the piston 5 up-stroke with the suction valve 11 closed with the aid of pressure rising in the cylinder 3, the gas can be compressed. In this manner, the suction valve 11 can be opened/closed by use of reciprocating motion of the piston 5.

By the above manner, since it becomes possible for suction gas to be inhaled from the lower part of the cylinder-wall of the cylinder 3 or the side face wall of the crankcase 1, the degree of freedom of gas inhalation design is increased, namely, the number of alternative selections of gas inhalation structure is increased.

FIG. 4, corresponding to FIG. 2, shows the fourth embodiment of the present invention.

In the fourth embodiment, the second cylinder volume 30 connected to the cylinder volume 9 is formed by the discharge side of the cylinder 3, and a volume adjusting piston 31 capable of piston movement is fitted into the second cylinder volume 30, while a spring 32 for restoration is set between the undersurface of the volume adjusting piston 31 and the base bottom of the second cylinder volume 30.

The other construction is the same as that of the above first embodiment, and the same part as that of the above first embodiment is quoted with the same reference number.

In case of the fourth embodiment, the cylinder dead volume can be redefined as the sum of the second cylinder volume 30 and the original cylinder dead volume which is the cylinder volume 9 in time when the piston 5 is at the top dead center. And the maximum discharge pressure can be adjusted so as to be compatible with the demand pressure of gas end use.

Moreover, since the second cylinder volume 30 connected to the cylinder volume 9 varies with the balance of the cylinder internal pressure force and the spring 32 force, it becomes possible to set the total volume of the second cylinder volume 30 and the original cylinder dead volume which is the cylinder volume 9 in time when the piston 5 is at the top dead center A. Also, it becomes possible for the maximum discharge pressure to be held automatically so as to meet the demand pressure of gas end use.

In the above embodiments, the explanation was focused on the reciprocating compressor which sends gas out to end use. However, the application style is not limited to gas sending. As a matter of course, the present invention is applicable to the reciprocating booster compressor to have the same mechanism as the reciprocating compressor of this invention.

The present invention makes it possible to provide a reciprocating compressor that is capable of holding the discharge pressure of the compressor so as to prevent the components of the compressor from breakage, and that is capable of always keeping the discharge pressure of the compressor at the target pressure in order not to violate the demand service pressure determined by the end-application conditions or specified limitations of instruments used downstream of the compressor, without the increase of part marks, processing man-hours and production costs.