US1994146A - Means for regulating compressors - Google Patents

Description

March 12, 1935. w. OCHEL 1,994,146

MEANS FOR REGULATING COMPRESSORS Filed April 7, 1954 4 Sheets-Sheet 2 INVENTOR K /L ATTORNEYS flan' ch 12, 1935o W. OCHEL MEANS FOR REGULATING COMPRESSORS Filed April 7, 1934 4 Sheets-Sheet 3 arch 12, 1935. W, QCHEL 1,994,146

MEANS FOR REGULATING COMPRESSORS Filed April 7, 1954 4 Sheets-Sheet 4 the suction valve,

UNITED STATES PATENT OFFI MEANS FOR REGULATING OOMPRESSORS Willy Ochel, Berlin-Wittenau,

to A. Borsig Maschinenbau, Germany,

8 Claims.

This invention relates to means for regulating the output of compressors and similar machines, and refers more particularly to a device utilizing compressed air, for maintaining the suction valve of a compressor open during a certain portion of the compression stroke of the latter.

In prior art, auxiliary pistons used for opening the suction valves of a compressor were arranged in the form of a separate device operated in synchronism with the compressor and actuated by separate driving means, such as oil or anelectrical current. These devices are quite complicated and expensive and in many instances they cannot be attached to ordinary compressors installed in factories and workshops.

An object of the present invention is the provision oi. a regulating device for compressors which can be easily installed and connected with compressors of the usual type.

Another object is the provision of means for regulating without stages the output of compressors and similar machines, which are operable without the necessity of using ating media.

any separate actu A further object is the provision of a regulating device which is simple in construction and inexpensive to manufacture.

The above and other objects of this invention may be realized by supplying air compressed during the compression stroke of the main piston to the surface of an aum'liary piston which is smaller in size than the operative surface of the suction valve, the pressure of said air, which is utilized for moving the auxiliary piston and thus actuating being adjus throttling device which may table by means of a be operated either automatically, for instance, depending upon the variations in pressure in the a The invention will appear ir tank, or by hand. more clearly from the following detailed description when taken in connection with the accompanying drawings showing preferred embodiments of the inventive idea.

In the drawings:

Figure 1 is a vertical section through a regulating device which is adjustable by hand.

Figure 2 shows on a larger scale a portion of the device illustrated in Figure 1.

Figure 3 shows diagramma tically an air compressure in the air tank.

Figure 4 is a vertical section through the regulating device illustrated di Figure 3.

rammatically in Germany, assignor A.-G., Berlin-Tegel,

a corporation of Germany Figure 5 is a similar view to Figure 4 and shows various parts of the regulating device in difierent positions. v

The device illustrated in Figures 1 and 2 of the drawings, comprises a compressor cylinder surrounding a piston 11 connected with a piston rod 12. The suction valve of the compressor, which is generally designated by the numeral 13 comprises a valve disc 14 situated within an opening 15 formed in the cylinder 10. The valve disc 14 is connected by a valve stem 16 with an auxiliary piston 17 and has a larger diameter than the piston 17.

A casing 18 surrounds the valve stem 16 and the piston 17 and is carried by the cylinder 10. A coiled spring 19 is situated within the casing 18 and presses on one side against the lower surface of the piston 17 and on the other side against a valve seat 20 screwed into the casing 18 and provided with openings 21. A hollow pipe 22 is attached to the casing 18.

Another hollow casing 23 is carried by the easing 18 and forms a chamber 24, communicating through an opening 25 formed in the casing 18 with a chamber 26, which is also formed in the casing 18 and which contains the spring 19 and the valve stem 16.

A coiled spring 27 is situated within the chamber 24 and supports a ball 28, used as a throttling device. A bore hole 29 formed in the casing 23 leads to the chamber 24. A cover 30 which is placed upon the casing 23 carries an adjustable bolt 31. The lower end of the bolt 31 is rigidly connected with a finger 32 which may be made of a single piece with the bolt 31; the lower end of the finger 32 may be brought into contact with the ball 28.

The casing 23 is also provided with a channel 33 which is in communication with a pipe 34 connected by the pipe 35 with a pipe 36 leading to the interior 37 of the cylinder 10.

The cylinder 10 is also provided with an outlet valve 38 comprising a valve disc 39 supported by a. spring 40 within a casing 41 connected with the cylinder 10. The valve stem 42 of the valve 38 is guided in the support 43. A pipe 44 is used as an outlet for compressed air and may be connected with an air tank which is not shown in the drawings.

During the normal suction stroke of the piston 11, the latter moves from the left to right (looking in the disclosure of Figure 1), the valve 13 is open and fresh air flows through the pipe 22 and the suction valve 13 into the chamber 37 of the cylinder 10.

During the normal compression stroke 1. e. when the piston is moving from right to left (looking in the disclosure of Figure 1), the valve 13 should be closed, the valve 38 is open and compressed airflows through the valve 38 into the pipe 44. However, a part of the compressed air will flow through the pipes 36, 35 and 34 and the channel 33 into the bore hole 29. This air will press upon the ball 28 moving it downward, and compressing the spring 27, so that a passage will be formed between the ball 28 and the adjacent walls of the bore hole 29. Then compressed air will be able to flow through the chamber 24 into the opening 25 and thus come in contact with the upper surface of the piston 17.

During the normal compression stroke of the piston 11, the air pressing upon the piston 1'7 will not be able to open the valve 13, since the air which is in contact with the piston 1'7 has the same pressure as the air filling the chamber 37 and pressing upon the valve disc 14. Since the operative surface of the valve disc 14 is larger than the operative surface of the piston 17, while the pressures upon the two surfaces are the same, the resultant force will tend to press the valve disc 14 against the valve seat 20, thus maintaining the suction valve 13 closed.

In the position shown in Figure 1 of the drawings, the lower end of the finger 32 is situated within the bore hole 29 and cannot come in contact with the ball 28, so that the ball 28 is free to move within the chamber 24. In this position the compressor will run empty, without performing any useful work, as will be explained hereinafter.

When the finger 32 is in the position shown in Fig. .1, and when upon the completion of the compression stroke the piston 11 begins to move from left to right, the pressure within the pipes 36, 35 and 34 will suddenly drop, so that the pressure in the chamber 24 will become higher than the pressure within the bore hole 29. Due to this higher pressure in the chamber 24 and to the action of the spring 2'7, the ball 28 will be pressed upward and will close the bore hole 29, thus interrupting the communication between the chamber 24 and the bore hole 29 connected with the channel 33.

The ball 28 closes the chamber 24, so that compressed air situated in this chamber continues to exert the same pressure upon the piston 17. In the meantime, no pressure is exerted upon the valve disc 14, so that the valve stem 16 moves downward compressing the spring 19 and permitting atmospheric air to flow through the pipe 22 and the openings 21 into the chamber 3'7 of the compressor. This position is shown in Fig. 1.

During the next compression stroke of the piston 11, compressed air within the chamber 24 will continue to press against the piston 17 while the air within the chamber 37 will be forced by the piston 11 to fiow through the openings 21 into the chamber 26.

Consequently, during this compression stroke of the piston 11 all the air will be driven out through the open valve 13 and the pipe 22, with the result that the compressor will operate without performing any useful work. It will be seen, therefore, that in the position shown in Figure 1, the regulating device prevents the piston 11 from supplying any compressed air to the air tank.

In the position shown in full lines in Figure 2 of the drawings, the bolt 31 has been screwed further into the bore hole 29, in comparison with its position shown in Figure 1. In Figure 2, the lower end of the finger 32 forming a part of the bolt 31 prevents the ball 28 from being pressed against the walls of the bore hole 29 and from closing this bore hole.

It the bolt 31 is situated in the position shown in Fig. 2, the device will operate as follows:

During the compression stroke of the piston 11, compressed air will flow through the pipes 36, 35 and 34 into the chamber '24. The pressure upon the piston 17 will be the same as the pressure on the valve disc 14 and since the operative surface of the valve disc 14 is greater than that of the piston 17, the valve 13 will remain closed.

During the return stroke or the suction stroke of the piston 11 both the piston 17 and the valve disc 14 will be under sub-atmospheric pressure. Since the chamber 26 is always in communication with the atmospheric air through the pipe 22, the pressure of atmospheric air will cause the valve stem 16 to move downward so that the suction valve 13 will open.

At the beginning of the next compression stroke, the valve 13 will close again, since the piston 1'7 and the valve disc 14 are subjected to the same pressure and since the operative surface of the valve disc 14 is greater than that of the piston 17.

Therefore, if the bolt 31 is in the position shown in full lines in Figure 2, the compressor produces the maximum amount of compressed air and it operates without being influenced by the regulating device.

Obviously, the positions of the bolt 31 shown in full lines in Figures 1 and 2, are the two extreme positions. In actual practice, the bolt 31 is adjusted by hand to some intermediate position, depending upon the desired amount of output of the compressor.

For instance, the bolt 31 may be moved downward from the position shown in Figure 1 to the position shown by broken lines in Figure 2. In the latter position, when the ball 28 is pressed upward against the finger 32, a very small slit is formed between the surfaces of the ball 28 and the side walls of the bore hole 29.

In the position shown by broken lines 120 in Figure 2, the ball 28 operates as a throttling device permitting a certain amount of compressed air in the chamber 24 to flow back through the pipes 34. 35 and 36 into the chamber 37 during the suction stroke of the piston 11 and during a certain part of the compression stroke of the piston 11. This constant flow of compressed air out of the chamber 24 will cause a slow drop in pressure in this chamber.

In the beginning of the compression stroke, the valve 13 will remain open so that the piston 11 will cause the air in the chamber 3'1 to flow into the chamber 26 and the pipe 22. However, the pressure upon the piston 17 will gradually diminish until a point is reached when the pressure upon the valve disc 14 will overcome the pressure upon the piston 17. Then the valve stem 16 will move upward and the valve 13 will close. The valve 13 will close sometime during the compression stroke of the piston 11; it may close sooner or later, depending upon the width of the slit between the ball 28 and the bore hole 29. Consequently, by placing the bolt 31 in such a position that the ball 28 is permitted to operate as a throttling device, the time at which the valve 13 closes is shifted from the beginning of the compression stroke to a certain point during the compression stroke. Therefore, by adjusting by hand the position of the bolt 31, it is possible to keep open the suction valve 13 during a predetermined part of the compression stroke of the piston 11.

The compressor runs empty while the. valve 13 is open since the air in the chamber 37 is driven through the openings 21 into the pipe 22. During the remaining part of the compression stroke i. e. while the valve 13 is closed the piston performs useful work by compressing air which passes through the valve 38 into an air tank not shown in the drawings.

The output of the compressor is consequently regulated by adjusting the position of the bolt 31. The amount of compressed air may be changed form a maximum output, during which the bolt 31 is situated in the position shown in full lines in Figure 2, to any number of smaller amounts and finally may be reduced to nothing by placing the bolt 31 in the position shown in Figure 1 of the drawings.

The regulating device shown in Figures 3, 4 and 5 of the drawings, operates automatically, depending upon the variations in pressure of the compressed air in the air tank of the compressor.

The compressor shown in Figure 3, is driven by a motor 51, which drives a fly wheel 52 by means of a belt transmission 53. The fly wheel 52 is connected with a rod 53', which drives the cross-head 54 connected with the piston rod 55 of the compressor 50. The compressor 50 is connected by a pipe 56 with an air tank 57 carried by the support 58. The motor 51 is carried by the support 59, while the compressor 50 and the fly-wheel 52 are carried by the support 60.

The compressor 50 comprises a piston 62 (Figure 4) reciprocating within the cylinder 61 and connected with the piston rod 55. The cylinder 61 carries a suction valve 63 which is connected with a pipe 64 leading to the air filter 65 (Fig. 3).

As shown in Figures 4 and 5, the valve 63 comprises a valve disc 66 connected by the valve stem 67 with an auxiliary piston 68, which is situated within a chamber 69. A coiled spring 70 surrounds the valve stem 67. Pipes 71 connect the suction valve 63 with a non-return valve 72 comprising a casing 73 provided with channels 74, 75 and 76.

A valve disc 77 rigidly connected with the valve stem 78 is situated within a chamber 79 surrounded by the casing 73. A coiled spring 80 surrounding the valve stem 78 is also situated within the chamber 79.

A pipe 81 connects the chamber 82 of the cylinder 61 with the conduit 74 formed in the casing 73. The conduit 74 which may be connected by the opening 83 with the chamber 79 is also connected with a pipe 84 leading to a casing 85.

As shown in Figures 4 and 5, the casing 85 is carried by a flange 86 of a cylindrical casing 87 surrounded by a casing 88. The casing 87 surrounds a chamber 89, while an annular chamber is formed between the walls of the casings s7 and as.

A plate 91 integral with the casing 88 carries the casing 87 and is provided with a channel 92, which connects the chamber 89 with the chamber 90. As shown in Figure 3, the plate 91 is carried by the support 93.

Pipes 94 connect the channel 76 formed in the casing 73 withthe casing 85.

A pipe 95 is connected with the casing 88 and carries a valve 96, shown in Figure 3. The opposite end of the pipe 951s connected with a tank which is not shown in the drawings, and

which is filled with a gas, having a constant pressure.

Another pipe 97 is attached to the walls-of the casing 88 and is connected with a manometer or pressure gauge 98, indicating the amount of pressure within the chamber 90.

An auxiliary piston 99 is situated within a bore hole or chamber formed in the casing 85. Parts of this bore hole are wider than the piston 99 and form annular chambers 100 and 101 surrounding this piston. Interconnected conduits or channels 102, 103 and 104 are formed in the piston 99. A channel or conduit 105.is formed in the casing 85 and is used for connecting the pipe 94 with the chamber 100. Another channel 106 is also formed in the casing 85 and is used for connecting the pipe 84 with the chamber 101.

A groove 107 is formed adjacent to the channel 106 in one of the inner walls of the casing 85. The piston 99 is provided with an edge 108, which cooperates with the groove 107 in a manner which will be explained hereinafter.

The lower end of the piston 99 is connected by a plate 109 with another plate 110 situated within the chamber 89 and serving as a cover for an expansible and contractible bellows 111. The lower end of the bellows 111 is connected with the plate 112 which is firmly attached to the plate 91 and which is provided with an opening 113 connecting the channel 92 with the interior of the bellows 111.

Another channel 114 is formed within the casing 85 and is connected by an opening 115 with the chamber 89. The channel 114 communicates with a pipe 116 leading to the air tank 57 (Fig. 3).

If the pressure within the air tank 57 does not exceed a certain predetermined amount, the piston 99 will have the position shown in Figure 4. Then the device will operate as follows:

During the compression stroke of the piston 62 i. e during the movement of the piston from left to right (looking in the direction of Figure 4) the air compressed by the piston will flow through the outlet valve 119 which is indicated diagrammatically in the drawings, and the pipes 56 into the air tank 57. A part of the compressed air will flow through the pipe 81 into the channel 74 formed in the valve casing 73. The air will press against the valve disc 77 and will move it downward, compressing the coiled spring 80.

Then the chamber 79 will be connected with the channel 74, so that the air will flow through the opening 83, the chamber 79 and the channel 76 into the pipes 94; the compressed air will penetrate into the interior of the casing 85 and will flow through the channel 105 into the chamber '100 and then through the channels 102, 103 and 104 of the piston 99 into the chamber 101 of the casing 85. From there, compressed air will flow through the channel 106 into the pipe 84 and return to the channel 74 of the valve 72.

A part of the compressed air flowing through the chamber 79 of the valve 72 will also flow through the channel 75 and the pipe 71 into the chamber 69 of the valve 63, coming in contact with a surface of the piston 68.

The pressure in the chamber 69 below the pistons 68 will be, consequently, the same as the pressure in the chamber 82 of the cylinder 61. Since the operative surface of the piston 68 1. e. that surface of the piston which is in contact with the compressed air, is smaller than the operative surface of the valvedisc 66, the valve disc 66 will be pressed downward against its seat so that the suction valve 63 will remain closed during the compression stroke of the piston 62.

In the beginning of the suction stroke of the piston 62 i. e. when the piston 62 begins to move from right to left (looking in the direction of Fig. 4) there is a substantial drop in pressure in the chamber 82, the pipe 81 and the channel 74. The spring will press the valve disc 77 upward and the communication between the chamber 79 and the channel 74 will be interrupted. This position is shown in Figure 4 of the drawings.

Compressed air within the chamber 69 of the valve 63 will flow back through the pipes 71, the

channel 75, the chamber 79, the channel 76, the

pipes 94, the channel 105, the chamber 100, the channels 102, 103, 104, the chamber 101, the channel 106, and the pipe 84 into the channel 74 of the valve 72. The air in the channel 74 will flow through the pipe 81 back into the compressor chamber 82.

Since the chamber 82 is under sub-atmospheric pressure, while the 'pipe 64 supplies atmospheric air into the interior of the valve 63, the valve stem 67 will move upward into the position shown in Figure 5, and the suction valve 63will open.

At .the beginning of the next compression stroke, the suction valve 63 will close again and it will open again during the next suction stroke. The suction valve 63 will be closed during the entire compression stroke and open during the entire suction stroke, so that the output of the compressor will be a maximum one.

The interior of the bellows 111 is always maintained under a constant pressure by an auxiliary gas which is introduced through the pipe 95, the

chamber 90, the channel 92 and the opening 113 into the interior of the bellows 111, and the pressure of which is indicated by the manometer 98.

,Should the pressure in the air tank 57 increase above a certain predetermined amount, the air having this increased pressure will flow from the air tank 57 through the pipe 116 and the channels 114 and 115 into the chamber 89, and will press against the plate 110. The forces acting upon the plate 110 from the outside of the bellows 111 will be greater than the forces acting upon the plate 110 from the inside of the bellows, so that the bellows will be compressed and will move downward along with the plates 110 and 109 and the piston 99.

In the position shown in full lines in Figure 5, the increased pressure within the air tank 57 has compressed the bellows 111 to such an extent that the edge 108 of the piston 99 has been moved below the groove 107 of the casing in this position there is no communication between the air in the groove 107 and the air in the channel 104.

If the piston 99 is situated in .the position shown in full lines in Fig. 5, a part of the air compressed by the piston 62 (Fig. 4) during the compression stroke of the latter, will flow through the pipe 81 into the channel 74 and. will press downward the valve disc 77; the air will flow through the chamber 79, the channel 76, the pipes 94, the channel 105, the chamber 100 and the channels 102 and 103 into the channel 104. Since there is no communication between the channel 104 and the chamber 101, the air within the channel 104 will not be able to flow into the channel 106.

A part of the compressed air flowing through the chamber 79 will pass into the channel 75 and will reach the chamber 69 through the pipes 71,

so that the pressure in the chamber 69 will be the same as the pressure in the chamber 82.

At the beginning of the suction stroke or the piston 62, the compressed air within the channel 74 and the pipe 81 will return to the cylinder 5 chamber 82 and the valve 72 will close so that the communication between the chamber 79 and the channel 74 will be interrupted.

However, compressed air within the chamber 69 of the valve 63 will not be able to return to the chamber 82, since the pipes 71 and 94 are not connected any more with the pipe 84. This compressed air is confined within the chamber 69, the pipes 71, the channel 75, the chamber 79, the channel 76, the pipes 94, the channel 105, the chamber 100 and the channels 102, 103 and 104.

The suction valve 63 will open at the beginningof the suction stroke of the piston 62 due to the pressure of compressed air within the chamber 69.

During the following compression stroke or the piston 62, an additional amount of compressed air which lowers the valve disc 77 and flows through the pipe 81, the channel 74, the opening 83, the chamber 79, the channel 75 and the pipe 71 into the chamber 69, will increase the pressure within the chamber 69. The suction valve 63 will stay open during the entire compression stroke of the piston 62. This position is illustrated in Figure 5 of the drawings.

In this position the compressor does not perform any useful work, since the air driven out of the chamber 82 by the piston 62 will flow back into the pipe 64 through the open valve 63.

If the pressure within the air tank 57 is higher than the required normal pressure, but smaller than that pressure which causes the piston 99 to assume the position shown in full lines in Fig. 5, the piston 99 may assume any one of the intermediate positions, for instance, the position shown by broken lines in Figure 5. In this position, the channel 104 is connected with the channel 106, but the cross-sectional area of the groove 107 interconnecting the two channels is so small, that the piston 99 will operate as a throttling device.

After the completion of the suction stroke and during a part of the compression stroke, the valve 63 will remain open while compressed air within the chamber 69 will flow slowly into the cylinder 61 through channels formed in the valve 72, the piston 99 and the casing 85. When a certain part of the compression stroke has been completed, the pressure within the chamber 69 will drop to such an extent that the spring 70 will be able to move the piston 68 downward and to press the valve disc 66 against its valve seat, thus closing the 55 valve 63. During the remaining part of the compression stroke the piston 62 performs useful work, driving compressed air through the outlet valve 119 and the pipe 56 into the tank 57.

Therefore, while the piston 99 operates as a throttling device, the piston 62 will compress air only during a certain part of its compression stroke, the relation between this part of the compression stroke and the total stroke depending upon the position of the piston 99 within the casing 85.

The suction valve 63 remains open while the air pressure within the chamber 69 is greater than the pressure within the chamber 82 of the cylinder 61 and the pressure exerted upon the spring 70 upon the piston 68.

If the pressure in the air tank 57 has increased to such an extent that the piston 99 will remain for a considerable period of time in the position shown in full lines in Figure 5, the pressure within the chamber 69will drop slowly due to leakage in the various elements of the regulating system.

This drop in pressure will continue until the spring 70 will be able to close the valve 63, so that during the next compression stroke of the piston 62 more compressed air will flow into the air tank 57 and the pressure in the air tank will increase still further.

Air having this increased pressure will flow into the chamber 89 and will compress still further the bellows 111; the piston 99 will move further downward until a connection is established between the channel 104 of the piston 99 and the channel 114 leading to the air tank 57.

Then compressed air in the air tank 57 will flow through the pipe 116, the channels 114, 104, 103- and 102, the chamber 100, the channel 105, the pipe 94, the channel 76, the chamber 79, the channel 75 and the pipes 71 into the chamber 69. This high pressure will cause the valve 63 to open immediately, so that from that time on the compressor will run empty.

It will be noted that the regulating device illustrated in Figures 3 to 5 of the drawings, operates in a similar manner to the device illustrated in Figures 1 and 2, an important distinction being that the functions of the ball 28 shown in Figures 1 and 2, are assumed by two separate elements, namely the throttling devices 85, 99 and the valve 72.

These regulating devices keep the suction valves open even when the air tank pressure has increased only to a slight extent above its predetermined normal pressure. The devices which close the suction valves when the pressure in the air tank has returned to normal, operate immediately without being retarded by frictional forces or by inertia.

The output of compressors isregulatedwithout stages, since the regulating devices respond to very small changes in pressure.

What is claimed is:

1. In combination with a compressor cylinder, a reciprocating piston within said cylinder, and a suction valve connected with said cylinder, an auxiliary piston connected with said suction valve, means connected with said cylinder for supplying compressed gas to a surface of said auxiliary piston during the compression stroke of the compressor piston," said surface being smaller than the operative surface of said suction valve, said means comprising a throttling device; and means connected with said throttling device for adjusting the same depending upon the desired output of the compressor cylinder, the compressed gas supplied to said aumliary piston keeping the suction valve open during a part of the compression stroke of the compressor piston.

2. In combination with a compressor cylinder, a reciprocating piston within said cylinder and a suction valve connected with said cylinder, said suction valve comprising a valve disc movable within said cylinder and a valve stem connected with said valve disc; an auxiliary piston connected with said valve stem and movable therewith, the diameter of said auxiliary piston being smaller than that of said valve disc, a casing enclosing said auxiliary piston, a throttling device, means connecting said throttling device with the interior of said compressor, said throttling device comprising means for transmitting compressed gas from the first-mentioned means to the interior of said casing, the last-mentioned means forming a passage for the compressed gas, and means for diminishing the cross-sectional area of said passage and for closing said passage; and means connected with the lastmentioned means for adjusting the same.

3. In combination with a compressor cylinder, a reciprocating piston within said cylinder, and a suction valve connected with said cylinder and comprising a valve disc movable within said cylinder and a valve stem connected with said valve disc; an auxiliary piston connected with said valve stem and having a diameter which is smaller than that of said valve disc, a casing enclosing said auxiliary piston, a spring surrounding said valve stem, another hollow casing connected with the first-mentioned casing and having an opening for the passage of compressed gas, a spring within the second-mentioned casing, a ball carried by the second-mentioned spring and adapted to close said opening, a movable bolt carried by the second-mentioned casing, a finger connected with said bolt and adapted to come in contact with said ball to prevent it from closing said opening, and pipes connecting said cylinder with the second-mentioned casing and adapted to supply compressed gas to said opening.

4. In combination with a compressor cylinder, a reciprocating piston within said cylinder, and a suction valve connected with said cylinder; a casing surrounding a chamber, another piston movable within said chamber, said casing having a groove formed adjacent to the second-mentioned piston, and a channel communicating with said groove, means connected with said casing and said cylinder and adapted to transmit a gas from said groove to the interior of said cylinder and vice -versa, an auxiliary piston connected with said suction valve, a casing enclosing said auxiliary piston, the second-mentioned piston having a channel and an edge codperating with said groove, the movements of the second-mentioned piston varying the cross-sectional area of a passage formed between said groove and said edge, and means connecting the first-mentioned casing with the second-mentioned casing and adapted to transmit compressed gas from the channel formed in the second-mentioned piston to the interior of the second mentioned casing and vice versa.

5. In combination with a compressor cylinder, a reciprocating piston within said cylinder, and a suction valve connected with said cylinder; a casing surrounding a chamber, another piston movable within said chamber, said casing having a groove formed adjacent to the second-mentioned piston and a channel communicating with said groove, an auxiliary piston connected with said suction valve, a casing enclosing said auxiliary piston, the second-mentioned piston having a channel and an edge 00- operating with said groove, the movements of the second-mentioned piston varying the cross-sectional area of a passage formed between said groove and said edge, means connected with said casing and said cylinder and adapted to transmit a gas from said groove to the interior of said cylinder and vice versa, means connecting the firstmentioned casing with the second-mentioned casing and adapted to transmit compressed gas from the channel formed in the second-mentioned piston to the interior of the second mentioned casing and vice versa, and means operatively connecting the first-mentioned means with the second-mentioned means when the pressure of a gas in said cylinder has increased above a predetermined amount.

6. In combination with a compressor cylinder, a reciprocating piston within said cylinder, a suction valve connected with said cylinder, and a tank for compressed gas connected with said cylinder; an auxiliary piston connected with said suction valve and movable therewith, a casing, a piston movable within said casing and having a channel, said casing having a plurality of channels communicating with the first-mentioned channel in some of the positions of the last-mentioned piston within said casing, means connecting one of the second-mentioned channels with the compressor 'cylinder, another casing surrounding said auxiliary piston, means connecting another one of the second-mentioned channels with the second-mentioned casing, means connecting a third one of the second-mentioned channels withsaid tank, and means connected with the third one of the second-mentioned channels and moving the second-mentioned piston in accordance with the pressure of the gas in said tank, the first-mentioned channel interconnecting the second mentioned means with the third-mentioned means in a position of the lastmentioned piston corresponding to a high pressure of the gas in said tank.

7. In combination with a compressor cylinder, a reciprocating piston within said cylinder, a suction valve connected with said cylinder, said suction valve comprising a valve disc movable within said cylinder, and a valve stem connected with said valve disc; and a tank for compressed gas connected with said cylinder; an auxiliary piston connected with said valve stem and having a diameter which is smaller than the diameter of said valve disc, a. casing enclosing said auxiliary piston, another casing having a chamber and a channel connected with said chamber; a valve disc within said chamber, resilient means situated within said chamber and adapted to move the last-mentioned valve disc to interrupt the communication between said chamber and said channel, means connecting said cylinder with said channel, means connecting the firstmentioned casing with said chamber, a third casing having a chamber and a channel connected with said chamber; means connecting the firstmentioned channel with the second-mentioned channel, a movable piston situated within the last-mentioned chamber and having a channel formed therein, the third-mentioned channel communicating with the second-mentioned channel at certain positions of the last-mentioned piston, means connecting the first-mentioned chamber with the third-mentioned channel, and means connected with said tank and the last-mentioned piston for moving thelatter in accordance with the pressure of the gas in said tank.

8. In combination with a compressor cylinder, a reciprocating piston within said cylinder, a suction valve connected with said cylinder, said suction valve comprising a valve disc movable within said cylinder, and a valve stem connected with said valve disc; and a tank for compressed gas connected with said cylinder; an auxiliary piston connected with said valve stem, and having a diameter which is smaller than the diameter of said valve disc, a casing enclosing said auxiliary piston, another casing having a chamber and a channel connected with said chamber; a valve disc within said chamber, resilient means situated within said chamber and adapted to move the last-mentioned valve disc to interrupt the communication between said chamber and said channel, means connecting said cylinder with said channel, means connecting the first-mentioned casing with said chamber, a third casing having a chamber and a charmel connected with said chamber; means connecting the first-mentioned channel with the second-mentioned channel, a movable piston situated within the lastmentioned chamber and having a channel formed therein, the third-mentioned channel communi-- eating with the second-mentioned channel at certain positions of the last-mentioned piston, means connecting the first-mentioned chamber with the third-mentioned channel, a fourth hollow casing connected with the third-mentioned casing, means connected with said tank and the third-mentioned casing and adapted to transmit compressed gas from said tank to the interior of the last-mentioned casing, an expansible and contractible bellows diaphragm situated within the last-mentioned casing and operatively connected with the last-mentioned piston, and means maintaing the interior of said bellows diaphragm under a constant gas pressure.

WHILY OCHEL.

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