US2141069A

US2141069A - Compressor unloader

Info

Publication number: US2141069A
Application number: US110678A
Authority: US
Inventors: George K Newell
Original assignee: Westinghouse Air Brake Co
Current assignee: Westinghouse Air Brake Co
Priority date: 1936-11-13
Filing date: 1936-11-13
Publication date: 1938-12-20
Anticipated expiration: 1955-12-20

Description

Dec. 20, 1938. K NEwELL 2,141,069

COMPRESSOR UNLOADER Filed Nov. 15, 1936 2 118 1 1 INVENTOR GEEIRGE K. NEWELL Q/fmxw.

ATTORN EY Dec. 20, 1938. G. K. NEWELL 2,141,069

COMPRES SOB UNLOADER Filed Nov. 15, 1936 2 Sheets-Sheet 2 Fig.5

w INVENTOR EEEIRGE K. NEWE LL BY%% w ATTORN EY Patented Basso, 193a NITE STATES 2,141,000 v I comrna'sson rmnoanan.

'amemneweu,

Pitcairn. rs, asaignor to The Westinghouse Ali-Brake company. Wilmer-ding,

2a., a corporation of Pennsylvania Application November 13, 1936, Serlal No. 110,678

I 4 Claims. Thisinvention relates to a fluid compressor and more particularlyto unloading means of a type adapted for use on a multi-stage compressor.

It is customary .to unload fluid compressors by maintaining the inlet valves unseated and thereby prevent the compressors from compressing fluid. The mechanism by'which the inlet valves are held unseated. is usually mounted in the inlet chambers of the cylinders to beunloaded. When the compressor is in the loaded condition, and is being operated to compress fluid, the'inlet chamber of the high pressure cylinder of a multi-stage compressor is supplied with fluid under pressure by the low pressure cylinder of the compressor. Unless the elements of the unloading mechanism are constructed with a high degree of accuracy, fluid ,under pressure will leak from the inlet chamber of the high pressure cylinder to the atmosphere past the unloading means associated with this cylinder, thereby reducing theefliciency and the output of the compressor.

It is an object of this invention to provide unloading means adapted for use in connection with the inlet valve of the high pressure cylinder of a two stage compressor, and incorporating means operative when the compressor is loaded to prevent the escape of fluid under pressure from the chamber in' which the inlet valve of the high pressure cylinder is mounted.

A further object of the invention is to provide improved compressor unloading means of the type described, and which is constructed so as to require a minimum of the parts thereof to be manufactured with a high degree of accuracy.

Another object of the invention is to provide improved compressor unloading means.

Other objects of the invention and features of novelty will be apparentfrom the following de-.

scription taken in connection with the accompanying drawings, in which,

Fig. 1 is a fragmentary view, largely in section, of a two stage compressor provided with unload- I ing means embodying this invention,.

Fig. 2 is an enlarged sectional view taken substantially along theline 2-2 of Fig. 1,

' Fig. 3 is a fragmentary view, largely in section, of a two stage compressor provided with a modified form of unloading means embodying ,this invention, and

Fig. 4 isan enlarged fragmentary view of the inlet valve assembly employed with the low pressure cylinder of the compressor shown in Fig. 3.

Referring to Fig. l of the drawings there is illustrated therein a portion of a fluid compressor i, which is driven by suitable means, not shown,

and which compresses fluid under pressure into a reservoir 2. p

The compressor I may be of any well known construction, and has a crankcase l to which are secured a low pressure cylinder 5, and a high pressure cylinder 8-. These cylinders have bores .therein in which are reciprocated pistons 8 and 9, respectively, by means of a crankshaft, not shown.

The low pressure cylinder 5 has a head ll detachably secured thereto and having a chamber Ii therein which is open to the atmosphere by Y way of a passage II. An inlet valve assembly indicated generally by the reference numeral II is mounted in the chamber II to control communication between this chamber and the compression chamber M at the upper face of the piston 8. i

The inletvalve assembly it comprises a seat member it having passages l'l extending therethrough, and having a seating face thereon which is adapted to be engaged by an annular valve It. The seat member It has a spring cage 20 secured thereto, while a coil spring 21 extends between the spring cage 20 and the valve II and yieldingly presses the valve l8 against the seating face on the seat member l6.

The seat member I8 is held in engagement with a shoulder on a cylinder head It! by means of a hollow threaded member 22 having passages 26 extending through the wall thereof, while a cover 24 is secured on the threaded member 22.

The cylinder head Ill also has formed therein an exhaust chamber 36 in which is mounted an exhaust valve assembly indicated generally by the reference numeral 3|, and comprising a seat member 32 having passages 34 extending therethrough, and having a seating face adapted to be engaged by an annular valve 26. A spring cage 38 is secured to the seat member 32, while a, coil spring 40 extends between the spring cage 38 and the valve 36 and yieldinglypresses the valve 36 into engagement with the seating face on the seat member 32.

The exhaust valve seat member 32 is held in engagement with a shoulder on the cylinder head l0 by means of a threaded member 42, while a cover 43v is secured on the exposed portion of the threaded member 42 and engages the cylinder head III to seal the threaded opening in which the member 42 is mounted. The wall of the threaded member 42 has passages, indicated at 44, extending therethrough.

The exhaust chamber 30 in the cylinder head It of the low pressure cylinder 5 is constantly connected by way of an inter-cooler 48 with the inlet chamber 48 formed in the cylinder head 88 of the high pressure cylinder 8.

The inlet chamber 48 has mounted therein an I inlet valve assembly indicated generally by the reference numeral 51 for controlling communication between the inlet chamber 48 and the compression chamber 52 at the face of the piston 8. The inlet valve 5| assembly comprises a" seat member 58 having passages 54 extending therethrough and having secured thereto a spring cage 55. The seat member 53 has a seating face A body 82 is secured on the exposed portion of the threaded member 58 and has a bore therein in which is mounted a valve piston 84 having a plurality of grooves in the wall thereof, one of the grooves being indicated at 68. The valve piston 64 has a seating face thereon which is adapted to engage a seat formed on the body 62 to cut of! communication between the inlet chamber 48 at the lower face of the valve piston, and a bore indicated at 88, which is constantly open to the atmosphere by way of a passage 88.

The valve piston 84 has secured thereto a stem 18, while a coil spring 12 extends between a flange II on the stem 18 and the seat member 53, and yieldingly urges the seating face on the valve piston 64 into engagement with the seat on the body 62.

A member I5 is slidably mounted on the stem I8 and has fingers 1.6 which extend through the passages 54 in the seat member 53 and engage the valve 58 to press it away from the seating face on the seat member 53 against the spring 58. The member 15 is yieldingly pressed into engagement with the flange II on the stem 18 by means of a coil spring 18.

The valve piston 64 has an upwardly extending stem 88 formed thereon which extends into a bore in a valve piston 82, which is slidablein the bore 88 in the body 62. The valve piston 82 has a seating face thereon which is adapted to engage a seat formed on the body 62 surrounding the bore 68 to cut oil communication between the bore 68 and a chamber 84 formed in a cover section 88, which is secured on the body62.

The chamber 84 is constantly connected by way of a pipe 88 with an unloading device 88 which operates in response to operating conditions of the compressor, such as the pressure of the fluid in the reservoir 2, the speed of the compressor, or other condition, to control the supply of fluid under pressure from the reservoir 2 to the chamber 84, and to also control the release of fluid from the chamber 84. The unloading device 88 may be of any well known construction, and one form of device which I may employ is shown in the application of Burton S. Aikman, Serial No. 4,094, filed January 30, 1935.

The head 58 of the high pressure cylinder 8 has an exhaust chamber 82 formed therein which is constantly connected by way of pipe 83 with the reservoir 2. The chamber 83 has mounted therein an exhaust valve assembly indicated generally by the reference numeral 84, and comprising a seat member 85 having passages 88 extend- 2.14.1,oo9 v ing therethrough, and having a seating face formed thereon which is adapted to be engaged by an annular valve 81. A spring cage 88 is secured to the seat member 85, while a spring 88 extends between the spring cage 88 and the valve 8'! and yieldingly presses the valve into engagement with the seating face on the seat member 85. v

The exhaust valve assembly 84 is held in position by means of a hollow threaded member I88 having passages I82 extending through the wall thereof, while a cover I84 is secured on the exposed portion of the threaded member I88.

The unloading meansprovided by this invention is adapted for use on compressors which are driven continuously and unloaded at intervals to prevent them fromcompressing' fluid when the pressure of the fluid compressed thereby increases loading device 88 connects the chamber 84 to the atmosphere, while the spring I2 presses through the stem 18 to hold the valve piston 84 against the seat on the body 52 to prevent flow of fluid from the inlet chamber 48 to the bore 88, and the stem.88- holds the valve piston 82 away from its seat. At this time the fingers I8 are held away from the valve 56, and the spring 58 holds the valve 5'8 against the seating face on the seat member 53.

On rotation of the compressor crankshaft, not

shown, the

pistons

8 and 8 are reciprocated in the

cylinders

5 and 6 respectively. On downward movement of the piston 8 fluid supplied from the atmosphere to the inlet chamber II in the head l8 of the low pressure cylinder 5 flows through the passages I1, unseats the valve l8, and flows to the compression chamber I4 at the upper face of the piston-8. On subsequent upward movement of the piston 8, the valve i8 is held seated by the spring 2 I, and the fluid in the compression chamber I 4 is compressed, and it moves the valve 38 against the spring 48 away from the seat member 32, and flows through the passages 34 to the exhaust chamber 38 from which it flows by way of the intercooler 46 to the inlet chamber 48 of the high pressure cylinder 6.

On downward movement of the piston 8 of the high pressure cylinder of the compressor, fluid supplied to the inlet chamber 48 flows through the passages 54, unseats the valve 56, and'fiows to the compression chamber 52 at the upper face of the piston 8. On subsequent upward movement of the piston 8 the fluid in the compression chamber 52 is compressed, and the valve 58 being held seated by the spring 58, this fluid is forced through the passages 86, unseats the valve 81, and flows to the exhaust chamber 82, from which it flows by way of the pipe 83 to the reservoir 2.

On the occurrence of the condition to which the unloading device 88 is designed to respond, such as an increase to a predetermined value in the Onanincseaseinthepressureofthefluidin thechamberlhthevalvepistonllismoveddownwardlyinthe bore ilinthebodyfl-until.

in, thereby cutting off commimication between the chamber {4 and the bore 4. in the body 42.

On downward movement of the valve piston.

'2 it presses against the stem ll and moves the valve piston 04 downwardly so that the seating face on this .valve piston is moved away from the seat on the body 02, with the result that comaunication is established between the inlet chamr 4| and the atmosphere-by way of the grooves 0' in the periphery of the valve piston 44, past the seat on the body I! to the bore. I8, and thence through the passage ll.

TOn downward movement of the valve piston 84 the spring II is compressed and exerts force an on the member I! to press the fingers ll against the valve It and move this valve away from the seating face on the seat 43 against the spring ll.

The compressor is now unloaded, and if it is gs operated it will not compress fluid into the reservoir'! sinc'e fluid supplied from the low pressure cylinder 6 to the intercooler 4t flows to the inlet chamber 48 of the high pressure cylinder I, and therefrom past the valve piston 04.

so to the bore and through the passage is to the atmosphere. As the fluid supplied from the low pressure cylinder 5 to the intercooler 4' may flow freelytherefrom to the atmosphere, no pressure will be developed in the intercooler 4t, and there 35 will be no opposition to upward movement of th piston l of the low pressure cylinder 5.

On downward movement of the piston 9 of the high pressure cylinder 8 while the compressor is unloaded, fluid drawn into the compression 40 chamber 52 past the open valve 56 on the suction stroke of the compressor is forced past the open valve .86 on upward movement of the piston O and throligh the passages 54\ to the inlet chamber 48, from which it may flow to the at- 5 mosphere past the valve piston 64,

As fluid may flow freely between the compression chamber 52 and the inlet chamber 48,and

also between the inlet chamber 48 and the atmosphere past the valve piston 64, no pressure will be developed in the compression chamber 12, and there will be no resistance to movement of the piston I in the cylinder 8. v

On the occurrence of the condition to which the unloading device Ill operates to load the compressor, such as a predetermined decrease in the pressure of the fluid in the reservoir 2, this device operates to cut off the supply of fluid under pressure from the reservoir 2 to the cham-. ber 84, and to connect the chamber 84 to the an atmosphere.

On' the release of fluid under pressure from the chamber 84, the force exerted thereby on the valve piston 82 and theyalve piston 64 is insuflicient to maintain these valve pistons g5 against the opposing force 'of the spring 12. The spring 12 thereupon moves the valve piston 64 upwardly so that the seating face thereon engages the seat' on the body surrounding the bore 68, while the valve piston I! is moved upwardly so that the seat thereon is moved away I of fluid between the inlet chamber l2! and the from the seat onthe body 62. I

On movement of the valve piston 64 to the seated position, communication between the inlet chamber 48 and the atmosphere iscut off so 75 that fluid under pressure supplied by the low gain 7 I n 3 pressure cylinder I to the intercooler 4! can no. longer escape to the atmosphere. I In addition, on movement of the valve piston '04 to the seated position, the flangell on. the

stem ll engages the member II and moves it 5 upwardly so that the fingers it are moved away from the valve It to permit the spring 88 to move the valve It into engagement with the seating face on the seat member If.

With the compressor rimning under the above conditions, the low pressure chamber I will supply fluid under pressure to the high pressure cylinder i, which in turn will supply fluid to the reservoir I in the, mannerdescribed in detail above.

It will be seen that this invention provides 5 unloading means for a multi-stage compressor, and that the unloading means operates to unload all of the compressor cylinders. It will also be seen that this unloading means incorporates valve means for releasing fluid from the inlet chamber of the high pressure cylinder, together with means operating through this valve means to unseat the inlet valve of the high press re cylinder. when the compressor is loaded this valve means permits the inlet valve of the high pressure cylinder toseat, while the valve means seats to prevent leakage of fluid from the high pressure cylinder inlet chamber to the atmosphere. w

In addition, when the compressor is unloaded the escape of fluid from the chamber to which fluid is supplied by the device for controlling the operation of the unloading means is prevented as the valve piston operated by the fluid supplied. to this chamber is held against a seat surrounding the bore in which the valve piston is mounted. I

It will be seen, therefore, as valve means is provided to prevent unintended escape of fluid from the inlet chamber of the high pressure cylinder when the compressor is loaded, and as other valve means is provided to prevent unintended escape of fluid from the chamber .to which fluid is supplied by the unloading means when the compressor is unloaded, there will be a minimum of leakage of fluid under pressure through the unloading means provided by this invention.

' In Fig. 3 there is illustrated a fluid compressor provided with a modified form, of unloading means embodying this iinvention. In this flgure of the drawings there is illustrated a fluid-compressor indicated generally by the reference numeral H0. This compressor is driven by suitable means, not'shown, and compresses fluid under pressure into a reservoir H2. The compressor H0 is similar to the compressor shown in Fig. l

of the drawings, and has a crankcase to which is secured a low pressure cylinder 5, and a high pressure cylinder 6. These cylinders have bores therein in which are reciprocated pistons H8 and 9, respectively. by means of a crankshaft, not shown.

The low pressure cylinder iii. has a head I! secured thereto having an inlet chamber Ill formed therein which is constantly connected to the atmosphere by way of a passage I12,

The inlet chamber |2l has mounted therein an inlet valve assembly, indicated generally by thereference numeral I25, to control the flow compression chamber I24 at the face of the piston H8. The inletvalve assembly comprises a seat member I26 having passages I21 extending therethrough. The seat member III has a seating face formed thereon which is adapted to be engaged by an annular valve I28. In addition, the seat member I26 has a central bore therein in which is mounted a valve I30 having a conical seating i'ace thereon which is adapted to engage aseat on the seat member I26 surrounding the bore in which the valve is mounted. The valve I 30 is of such diameter as to overlap the inner margin of the annular valve I28, and this valve is arranged so that when it is in the seated position, the valve I28 may engage the seating face on the seat member I26,

The valve I30 has a stem I32 extending therethrough, while a spring I34 extends between the seat member I 26 and a flange I36 on the stem I32 and yieldingly urges the stem upwardly so that the valve I30 is pressed against the seat member I26.

The stem I32 has a spring cage I38 secured to the lower end thereof, while a coil spring I40 extends between the spring cage I38 and the valve I28 and yieldingly presses the valve I28 against the seating face on the seat member I26.

The seat member I26 is held against a shoulder on the head I20 by means of a hollow threaded member I42 having passages I44 extending through the wall thereof. The member I42 has secured thereto a cover I46, which also engages the face of the head I20 to prevent the escape of fluid under pressure from the chamber I48 intermediate the cover and the member I42.

The member I42 has a bore therein in which is .mounted a valve piston I50 having an annular portion which closely fits the bore in the member I42, and having a conical sealing face thereon which is adapted to engage a seat formed on the member I42 surrounding the bore in which the valve piston is mounted.

The valve piston I50 has a round stem which extends into a' bore in the upper end of the stem I32. The various parts of the apparatus are arranged and proportioned so that the spring I34 may move the stem I32 upwardly, and move the valve I 30 into engagement with the seat on the seat member I 26 without moving the valve piston I50 into engagement with projections I52 formed on the cover I46.

The head I20 of the low pressure cylinder II5 has, in addition, an exhaust chamber I54 formed therein in which is mounted an exhaust valve assembly indicated generally by the reference numeral I56, and similar in construction to the exhaust valve assembly 3| employed on the low pressure cylinder 5 of the compressor shown in Fig. 1 of the drawings. The exhaust valve assembly I56 is held against a shoulder on the cylinder head I20 by means of a threaded memher I58, while a cover I60 is secured on the member I58.

The exhaust chamber I54 is constantly connected by way of an intercooler I62 with an inlet chamber I64 formed in the cylinder head I66 of the high pressure cylinder H6.

The inlet chamber I64 has mounted therein an inlet valve assembly indicated generally by the reference numeral I25a, and substantially identical in construction with the inlet valve assembly I25 employed on the low pressure cylinder H5.

The inlet valve I25a, is held in position against a shoulder on the cylinder head I66 by means of a hollow threaded member I10 having passages I12 extending through the wall thereof. A cover I14 is secured on the member I10 and cooperates therewith to form a chamber I16.

The member I10 has a bore extending therethrough, while a valve I18 is mounted in the inlet chamber I64, and is adapted to engage a seat on the member I10 surrounding the bore therein.

A valve I is mounted in the chamber I16 and is adapted to engage a seat formed on the member I10 surrounding the bore therein, and is also provided with an annular portion which closely fits the bore in the member I10. The valves I18 and I80 engage each other, and are proportioned so that when one of these valves is in the seated position, the other is held away from its seat.

A spring I82 extends between the valve I18 and the bottom of the bore in the stem I32a of the inlet valve I25a, and yieldingly presses the valve I18 to the seated position. The spring I82 is substantially weaker than the spring I34a associatedwith the stem I32a of the valve assembly I25a, so that when the spring I82 has moved the valve I18 to the seated position, it will not exert suflicient force on the stem I32a to move it against the spring I34a, and move the valve I30a away from its seat.

The cylinder 'head I66 of the high pressure.

cylinder II6 has an exhaust chamber I84 formed therein in which is mounted an exhaust valve assembly indicated generally by the reference numeral I56a, and substantially identical in construction with the exhaust valve assembly I56 employed on the low pressure cylinder H5. The exhaust valve assembly I56a is held against a shoulder on the cylinder head I66 by a threaded member I86, while a cover I88 is secured on the threaded member I86. The exhaust chamber I 84 is constantly connected by way of a passage and pipe I90 with the reservoir H2.

The compressor IIO has an unloading device I82 associated therewith. This unloading device may be of the same construction as the device 90 employed in connection with the compressor shown in Fig. l of the drawings, and controls the supply of fluid under pressure from the reservoir I I2 to the chambers I16 and I48 of the high and low pressure cylinders H6 and H5, respectively, and also controls the release of fluid under pressure from these chambers.

The compressor H0 is shown in the drawings in the loaded condition, and at this time the spring I34 associated with the inlet valve assembly I25 of the low pressure cylinder II5 operates through the stem I 32 to move the valve I30 to the seated position to permit the spring I40 to hold the valve I 28 in engagement with the seating face on the seat member I26; At this time the valve piston I 50 is held away from its seat.

In addition, at this time the spring I34a associated with the inlet valve assembly I25a of the high pressure cylinder II6 holds the stem I32a in a position to hold the valve I30a against its seat on the seat member I26a and permit the spring H011 to hold the valve I28a against the seating face on the seat member I26a, while the spring I82 holds the valve I18 against the seat on the member I10, and holds the valve I80 away from its seat.

With the compressor running, on downward movement of the piston II 8 of thelow pressure cylinder II5, fluid from the atmosphere will be drawn into the compression cylinder I24 above the piston II8 from the inlet chamber I 2I .past the valve I 28, which is moved away from its seat against the spring I40. On upward movement lllflows therefrom past 15 I, f 9, 41,000 a th'e pisto n Illthe'v'alv'ellti's held seated and this fluid iseompressed and flows past the exhaust valve assembly. I88 to the intercooler I82 and to the inlet I cylinder II8. At this time, as" the valve. I18. is held in the seated position, fluid cannot escape from the inlet chamber I88 to the chamber I18, and thence by way of the pipe I88-to the unloading device I82, through which it could escap to the atmosphere.

Ondcwnward movement of the piston 8 of the high pressure cylinder 8, fluid supplied by the low pressure cylinder I II to the inlet chamber the inlet valve assembly Illa to the compression chamber I88, and on subsequent upward movement or the piston III the fluid in the compression chamber I88 is compressed and'flows past the-exhaust valve assembly ma to the exhaust chamber I88, and thence by way or the pipe I88 to the reservoir II2. I On the occurrence of the condition to which the unloading device I82 is intended to respond, this device operates to cut oil! communication between the pipe I88 and the atmosphere, and to supply fluid under pressure from the reservoir I I2 to the pipe I88. 0n the supplyoi fluid under pressure to the pipe I88 fluid flows to the chamber I88 in the head I28 0! the low pressure cylinder Ill, and moves the valve piston I88 downwardly into engagement with the seat on the member I82 surrounding the bore in which the valve piston is mounted.

, On downward movement of'the valve piston I88 the stem thereof presses against the stem I82 and moves it downwardly against the spring I88, whfle the valve I88 is moved away from its seat and presses against'the valve I28 and 'moves it away from the seating face or the seat member I28 against the spring I88. j

In addition, on the supply of fluid under pressure to the pipe I88 fluid flows to the chamber I18 of the high pressure cylinder H8, and moves the valve I88 into engagement with the seat on the member I18, and this valve presses against the valve I18 and moves it away from its seat.

On slight downward movement of the valve 118 it engages the upper end oi the stem I82a so that on further downwardmovement of the valve I18, the stem I82a is moved downwardly against the spring Illa and moves the valve I884; away from its seat on the seat member I28a. On this movement of the valve 18811, the valve I280. is moved away iromthe seating face on the seat member 128a against the spring "8a.

The compressor is now unloaded and on downward movement of the piston I I8 01 the low pressure cylinder 5. fluid from the atmosphere will be drawn into the compression chamber I28 past sure cylinder I I8 is reciprocated, fluid under pres- I sure flows between the compression chamber I and the intercooler I82 past the valve l28a, which is held away from its seat, and insuflicient pressure is developed to cause fluid to be com pressedpast the exhaust valve assembly I58a into the exhaust chamber I88.

It will be seen that while the compressor is in the unloaded condition, the valvev piston I58 and the valve I88 are held firmly against their seats so.asto

chamber-I88 ot-the high pressure I88 and I18, respectively.

On the occurren caoi the condition which causes the unloading devi I82 to operate to eflect lordingoi the compressor, this device operates to cut oil the supply of fluid under pressure to the pipe I88, and to release fluid therefrom. On the release of fluid from the pipe' I88 fluid is reelased from the chambers I88 and I18. Onthe release of fluid from the chamber I88, the springllfl expands and operates through the stem I82 to move the valve I88. into engagement with the seat member I28 to permit the valve I28 to be movedto the seated position by the spring I88. In addition, on this movement of the stem I82, the valve piston I88 is moved away irom its seat.:

On the release of fluid fromthe pipe I88 fluid is prevent the leakage or fluid from the released from the chamber I18, and the spring Ifla expands and moves the stem I824; upwardly until the valve l88a engages the seat member the member I18, while the valve I88 is moved away from its seat.

The low pressure piston now operates to compress fluid into the intercooler I82 and the inlet chamber I88 of the high pressure cylinder II8, while the high pressure piston compresses fluid into the reservoir II2.

It will be seen that each of the cylinders has a valve subject to the pressure of the fluid supplied by the unloading device; and that on an increase.

in the pressure of the fluid supplied by this .de vice, these valves are moved to their seated positions to prevent the leakage of fluid supplied by t the unloading device through the bores in which these valve pistons are mounted.

In addition, it will be seen that the unloading means for the high pressure cylinderhas a valve through whichthe unloading means operates to a hold the inlet valve open, and which, when the unloading means is conditionedto' load the compressor, engages a seat to prevent leakage of fluid from the inlet chamber of the high pressure cylinder to the atmosphere through the unloading device. 1

While two embodiments of the improved com pressor unloading means provided by this invention have been illustrated and described in detail, it should be understoodthat the invention is not limited to these details of construction, and that numerous changes and modifications may be made without departing from the scope of the following claims. l

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. In a valve assembly for a fluid compressor,

a seat member having ports therethrough and having a central bore therein, an annular inlet valve engageable with a seat on said seat member to control the flow of fluid through said ports, and an element positioned in said central bore and adapted to engage a seat surrounding said bore, said element having a portion overlying the inner margin of said annular inlet valve and engageable therewith upon movement of said element away from its seated position to move said annular valve away from its seat on said seat member. Y

2. In a valve assembly for a fluid compressor, a seat member having ports therethrough and having a central bore therein, an annular inlet valve engageable with a seat on said seat member to control the flow of fluid through said ports, an element positioned in said central bore and adapted to engage a seat surrounding said bore, said element having a portion overlying the inner margin of said annular inlet valve and engageable therewith upon movement of said element away from its seated position to move said annular valve away from its seat on said seat member, and means yieldingly urging said element to the seated position.

3. In a valve assembly for a fluid compressor,

a seat member having ports therethrough and having a central bore therein, an annular inlet valve engageable with a seat on said seat member to control the flow of fluid through said ports, an element positioned in said central bore and adapted to engage a seat surrounding said bore, said element having a portion overlying the inner margin of said annular inlet valve and engageable therewith upon movement of said element away from its seated position to move said annular valve away from its seat on said seat member, and means yieldingly urging said inlet valve to the seated position.

4. In a valve assembly for a fluid compressor, a seat member having ports therethrough and having a central bore therein, an annular inlet valve engageable with a seat on said seat member to control the flow of fluid through said ports, an element positioned in said central bore and adapted to engage a seat surrounding said bore, said element having a portion overlying the inner margin of said annular inlet valve and engageable therewith upon movement of said element away from its seated position to move said annular valve away from its seat on said seat member, a spring seat carried by said element, and a spring extending between said spring seat and said annular valve for yieldingly pressing the inlet valve to the seated position.

GEORGE K. Nil-WELL.