US2167369A - Variable capacity compressor - Google Patents

Description

July 25, 1939. E. M. PAULLIN, JR

VARIABLE CAPACITY COMPRESSOR Filed Aug. 22, 1954 4 Sheets-Sheet i EMPaa/ll'n 61 INVENTOR A T TORNE Y E. M. PAULLI N, JR 7,

VARIABLE CAPACITY COMPRESSOR Filed Aug. 22, 1954. 4 Sheets-Sheet 5 R w m aw kw BMW M NM w I 0Q W Q 1 1 L 1 M .l-. .u an M flu m E. v Am w/ l M .kwfl .1. l X ma fi w km @Ng Gd 1 av v T as k I W A N U .1 Mm MT 69 0% 1 0% .J -I om mm 9w w. mv y 9v AM M July 25, 1939.

E. M. PAULLIN, JR

VARIABLE CAPACITY COMPRESSOR July 25, 1939.

Filed Aug. 22, 1954 4 Sheets-Sheet 4 Eff. Razz/2n (7i.-

IN VEN T OR A T ORNE Y Patented July 25, 1939 UNITED STATES PATENT OFFICE VARIABLE CAPACITY COLIPRESSOR Edward M. Paullin, Jr., Buffalo, N. Y., assignor to Worthington Pump and Machinery Corporation, New York, N. ginia Y., a corporation '0! Vir- Application August 22, 1934, Serial No. 740,869

13 Clai s.

This invention relates to variable capacity air or gas compressors, andan object of the invention is to provide a novel, relatively simple, automatically operated mechanism for loading and 5 unloading an air or gas compressor in predeter 1 mined percentages, of its fcapaclty, suchloading and unloadim being automatically controlled by Ware compressedflther before or charmer-em ssions in accordance with the] 10 load .demands .upon the compressor, thereby maintaining-practically constantthe suction pres- 1 sure or the receiver pressure.

' Another object or ,the present invention is to provide, in combination with an air or gas com- Q l a series of control or unloadin: valves each acting to control 'a partial loading v or unloading of the compressor cylinder or cylin- J I de'rsgsoas to vary the cylinder capacity in ac-':'

cordance with the number of control or unloadample, where a variance or pressure dlii'erential' of approximately two pounds is required in approved types of automatic unloading mechanisms now on the market, a .difierential of one-half pound or less will be suilicient in the present apparatus to effect a successive step in the loading or unloading of the compressor. I

' A further object 01' the invention isto provide an automatic load control mechanism .i'or air or gas compressors .whichis essentially electrically operated, the electric mechanism being in turn controlled by pressure operated mechanism and tom construct and-arrange thejva'rious electric 45 elements and electrically operated elements that hunting vor indecisive action of the unloading mechanisms will be eliminated andproper time, intervals will be provided to permit the efllcient and effective operationof. the control or unloads 5 ing valvesjior each step or fractional percentage j of compressor capacityi'i f j 'lth fih flnd o er" i tslavviewias' may appeartrrom e. tompa v nssb t pei invention" consists 'of jvarious fea ures of struction The electrically .9.1 ut he.

first described in connection with the accompanying drawings, showing a variable capacity compressor of the preferred form and the tea.- tures forming the invention will be specifically pointed out in the claims.

, In the drawings:

Fig. l is adiagrammatic view illustratingthe improved mechanism for controlling the loading and unloading'of an air or gas compressor.

' Fig. 2 is a detail section taken on the line 2-r-2 oi Fig. 1 and showing the switch operating cam.

line 3-4 of Fig. 1 showing a cam and illustratlng one of the electric circuitcontrolling contacts of the cams.

Fig. 4 is a vertical section taken on the lin 4-4 of Fig. 3. i Fig. 5 is a detail view partly in section and partly in elevation of one of the solenoid operated distributing valves. I

Fig. 6 is a detail of a latch mechanism an cam employed in the unloading mechanism.

Fig. 7 is a detail section through a pressure Fig. 3 is a detail cross section taken on theoperated device employed in the unloading mech- 1 anism.

Fig. 8 is a detail view and section oi. the differential gearing employed in the unloading mechanism.

Fig. 9 is a detail view of a control switch employed in the unloading mechanism which switch is the master control mechanism. I

eration of the master control switch.

Fig. 19 is a diagrammatic view illustrating a modified construction of the improved mechaof an air or gas compressor.

Referring more particularly tot he drawings, a

sure cylinder 2. These compressor.cylinders are loaded and unloaded in predetermined frac ous'control valves 3,4. 5, 6, l1 and 8. While. in the drawings, .theloading and unloading of the. compressor. cylinders is illustrated as being pro 1 vided through themediumof holding open suc- ,tionf'valvesjwhich are findicatedas the control tional percentages. of their capacity by-the variior the control valves, 111 and "8'f'rjespectively,lit to b understood,thatjtheimproved control 132mm; ormi t mesentirw 3'0 switch of the unloading 1 Figs. 10 to 18 are diagrammatic views illustrat-' I ing the difierent positions and manner of opor nism forcontrolling the loading and unloading multi-cylinder compressor is shown. comprising. the low pressure cylinder I and the high pres- In Fig. 1 of the drawings the various control valves of the cylinders I and 2 are shown com nected in pairs as for instance, the-control valves 3 and 5 are connected to each other and to the solenoid operated distributor valve structure it through the pipe M. The valves 6 and 6 are con nectedtogether and through the pipe It to the solenoid operated distributor valve I I while the valves I and 6 are connected through the pipe l'i with the solenoid operated distributor valve I 2,

thus the valves will operate in pairs to simultanecuslyunload both the low pressure cylinder 8 and the high. pressure cylinder 2 m me same predetermined percentage of capacity of the cylinders. a

.The solenoid operated valves 82, i5 and H are all similar in construction and 'are shown in detail in Fig. 5 of the drawings. Eachrof these distributor valve structures comprises a solenoid l8, the core B9 of which is connected through a suitable coupling 20 with the valve stops 2i and 22. In the deenergized position valvestop 25 is tight on its seat and valve stop 22 is open. Pressure fluid from any-suitable source, preferably from the receiver into whichthe fluid compressed is delivered, is delivered to the valve through the pipe 23 and passes to the unloadervalves through pipe H. The solenoid has been deenergized' by the governor mechanism hereinafter more fully described to permit fractional unloading of the compressor cylinders. When' the solenoid is energized valve stop 22 is held tightly against its seat, aided by receiver pressure, thus terminating the flow of fluid from the receiver. Valve stop 2! is open in this position and fluidpres- 5' sure, is released from the unloader valves through pipe II and out the release port 24. As, for example, when the solenoid I 8 of the distributor valve I2 is deenergized, pressure fluid will be delivered through the pipe 23, and pipe I I to the control valves 1 and 8 which will hold open the clearance pockets on the crank end of the cylinders I and 2 and permit the compressor to operate at seventy-five percent of its capacity since the capacity of the clearance pockets is substantially. one-half of the capacity of the crank end of the compressor.

When the solenoid l8 of the distributor valve ii is deenergized, the pressure fluid will be delivered to the control valves 3 and 5, which will 0 open the suction valves on the crank end of the cylinders l and 2 and permit the compressor to operate at fifty percent of its capacity.

When the receiver pressure is sufliiciently high,

the solenoids l8 of both of the distributor valves 5 I5 and II will be deenergized through the control mechanism hereinafter described and the suction valves of both cylinders will be held open which will permit the cylinders to operate at zero capacity. It isto be understood. of course,

that the present invention is not limited to any number of steps of fractional unloading of the cylinders but the improved control and unloading mechanism may be employed with any approved system of fractional unloading embodying i 7 any approved number of steps and that the construction shown and described herein is merely an example of one of such approved systems. Further, if desired, solenoid valves may be arranged so that unloading is accomplished by removing pressure from control valves and/or solenoid valves arranged to operate in this manner when energized or de energized. When the pressure falls, so that it is necessary to deliver more fluid compressed'to the receiver (not shown), the, various solenoids which have previously been deenergized will be energized, permitting the pressure fluid to bleed from the pipes II, M,

i6 and consequently from the respective control valves to atmosphere or compressor suction, permitting'the'closing of such valves and the loading of the compressor. The specific construction of the control valves will not be described in the present application-since they are relatively well known .and their specific construction is illustrated'and described in the prior patents hereinabove mentioned. 1 i i The present invention comprises'a novel-ar-' ran'gement of various mechanisms; both pressure and electricallyoperated for' controlling the energizing of the solenoids I8 of the various distributor valves, for timing theperiod of ener-- gization' of such solenoids,'and for operating'the control mechanism in suchmanner as to warrant ithighly sensitive to variations .or diiIer-; entials in receiver pressure or in pressure of fluid compressed so that the loading "andthe unload ing steps of the compressor may be eflected with much narrower or reduced differentials than has heretofore been possible. For instance, in'the various types of-apprcved compressor unloadin control governors heretofore devised, a difleren-' tial or variance of approximately two pounds-is required to efiect successive steps of loading or unloading-of the compressor cylinders, whereas the present mechanism will permit the 'efiecting of such successive steps on-a differential or variance of approximately one-half pound or even.

less, in the pressure of the fluidcompressed.

The invention herein explained provides also a means by which the pressure of a system may be returned to a predetermined average within a given time by changing the capacity of the compressor independent of the usual required ,change in fluid pressure but not rendering the governor at any time insensitive to a change in fluid pressure (should such a change occur occasioned by an increased or decreased demand for compressor capacity).

One end of the circuit of each of the solenoids I8 is connected through suitable electric conducting wires 25 with Li of the main current supply. The other end of the circuit of each of the solenoids is connected through wires 26 with the stationary contacts 21 of switch mechanisms 3|. The switch' mechanisms 3. include, besides the stationary.contacts 21, the movable blades II which carry the movable contacts 28. Each of the movable blades 3| is pivoted as shown at. and as moved by an eccentric cam 33 mounted upon the shaft 34 carries the contact 26 into engagement with the contact 21. The circuit through the solenoid is thereby completed through wire 29 ,to the other sideLs of the main current supply., The shaft H in bearings 35 is rotated by means of an electric motor 3'! through gear train 36. When the shaft 34 is rotated by operation of the motor 31, the various solenoids l8 will be energized. It is to be understood, 01' course, that the cams 38 are properly arranged upon the shaft 31 so that they will operate the 'through wire 38(for one rotation) or wire 39 (for reverse rotation) contact blade 40 of mechanism 42 (action to be explained below) and wire Contact blade 40 engages contact tip of wire .39 when flexedby the energizingof solenoid 43.

, Contactblade 40 will engage contact tip of wire 38 in a similar manner when solenoid 44 is energized.

.61., of lever.62 under the action of spring 63. -Motor 3! will'thenoperate until shaft 34 has [rotated cam 6 4.to a position where one of several extensions 65 will move lever 62 and yoke 6|, thus 25 releasing contact blade". The cam 64'and extensions 65 are arranged so that rotation of shaft .3.4.will be in predetermined steps or angular degrees of rotation, thus assuring positive and complete action of contacts 21 and 28. 7

One end of the circuit of solenoid 43 is connected through wire 45 to L2 of the main current one direction. Contact 60 is arranged so that'the electrical circuit in wire 41 will be interrupted when the limit of travel is reached in the reverse direction. V

The delivery of electrical current through the contact 48 or 49 from contact 59, wire 5| and L1 of the main current supply is controlled by the master control switch structure 80. The contact 58 is moved by the rod 52 which is in turn moved through the movement of the diaphragm operated lever 53 of the pressure operated mechanism 54. The pressure operated mechanism 54 is specifically shown in Fig. 7 of the drawings and also in some of the prior patents hereinabove mentioned. It comprises the housing 54 having the diaphragm 55 therein which diaphragm is acted upon by pressure fluid entering the housing through the pipe 56. This pipe 56 is preferably connected to the discharge receiver (not shown) into which the fluid compressed is delivered or the suction holder (not shown) from which the fluid to be compressed is taken so that movement of the diaphragm 55 and consequently movement of the contact 58 is controlled by the pressure of the fluid compressed. The contact 58 co-operates or contacts with-either of the 36 with the resultant deenergization oi the solenoid l8 connected in circuit with the switch thus operated.

Shaft 34 is connected through differential gear unit 66 .with shaft 14 supported by bearings 16. For each degree of rotation ofshaft 34, there is an equal or proportional rotation of shaft 14. Cam 16 will act through'roller 'l'l, lever 18 pivoted at 19, and master control switch structure 80 to reposition contacts 48' and 49 after each step in the operation of the governor, thus interrupting the electrical circuit to solenoids 43 and 44 and allowing cam 64 to act through lever 62 and release contact blade 48, thereby stopping motor 31.

Upon a further rise in pressure of fluid compressed, the contact 58 will be moved upwardly a greater distance and it will again contact with the movable contact 48 which has been previously repositioned in the manner explained and will be hereinafter further described. The second upward movement of the contact 58 will again' ond step in the unloading of the compressor.'

This operation is repeated as the pressure of fluid compressed rises until the compressor cyl-,

inders are completely unloaded. When the pressure of fluid compressed falls, however, the switch contact 50 will move downwardly into contact with the movable contact 49 and thus close a circuit througli the electromagnet 44 for operating the contact blade to move it into en-' gagement with the contact tip of wire 38 for energizing the motor 31 and causing it to rotate in a reverse direction, which will operate the respective cams 33 in a reverse direction and energize the solenoids E8 in the proper sequence to load the compressor in the proper steps.

It will be observed, therefore, that contacts 48 and 49, which are always a fixed distance apart, will assume a definite position with respect to any reference point in their plane, for each step in the operation of the governor. The successive positions during an unloading and loading cycle are as shown in Figures 10 to 18 inclusive. Fig. 10 is indicative of normal position. With an increase in-fluid pressure structure 52 is raised and contact 58 engages contact 48 as shown in Fig. 11. With the resulting operation of the governor, structure 80 will reposition contacts 48 and 49 as shown in Fig. 12. If the increase in pressure has raised structure 52 and contact 50 a suflicient distance, contact 58 will still engage contact 48 as shown. in Fig. 13 and the governor will move one additional step, repositioning contacts 49 and 49 and breaking the electrical circuit as shown in Fig. 14. With a decrease in fluid pressure, contact 50 will engage contact 49 as shown in Fig. 15. Contacts repositioned are shown in Fig. 16. On a further decrease in fluid pressure, contact 50 again engages contact 49, Fig. 17. Contacts 48 and 49 again in their normal position are shown in Fig. 18.

It is to be understood, of course, that the loading and unloading of the compressor and consequently the movement of the contacts 48 and 49 upwardly and downwardly is not necessarily regular, that is, the contacts are not necessarily moved upwardly in steps until they have-reached their uppermost position after which they start downwardly, but upon variances inthe pressure of the fluid they may move upwardly'one step or wardly again, etc.

stant, contact 88 will again engage contact 5% as in Fig. 11, resulting in a further decrease in compressor capacity. If the fluid pressure is returning to normal, contacts will assume positions as shown in Fig. 10 without a further decrease in compressor capacity. If the fluid pressure decreases below normal contact 58 will, of

course, engage contact 49 and increase the capacity of the compressor.

The result of this inverse repositioning or biasing action is a greatly decreased differential in fluid pressure, operation of the governor on each step at exactly the same pressure, and the ability to return fluid pressure in a system to normal although the demand for quantity of fluid has not changed. Theaction is accomplished by the introduction of a second motor 85 (reversible) which is connected to shaft It through the gear 86 and differential gear unit 66 driving only shaft it, which in turn through cam I5 and lever I8 will reposition switch structure 88 with contacts 88 and 69 independent of the repositioning due to an action of the governor brought about by motor 31. By the proper selection of gearing in 66 any desired timing may be obtained.

The operation of motor 85, which is, connected to L3 and through wire 83 or 84 and wire 82 to L1, is controlled by cam 8|, which is of the same construction as cam 58 but with contacts arranged so that motor 85 will be stopped when shaft M, cam I6 and contacts 48 and 49 are in their normal position only. At all other times the motor will be operating in one direction or the other, thereby returning contacts 68 and B9 to their normal position.

The differential gear unit 56, Fig. 8, consists essentially of gear 67 mounted on shaft 34 and gear I3 mounted on shaft It. 'Driving gear 68 and driving pinion 69 are. mounted on shaft I8. Gear I2 on shaft II connects gears 69 and I3. Gear'86 forming one side of the case of the differential unit is driven by motor85.

A general statement of the operation of the device, which operation has been specifically described hereinabove is; upon operation of the contact 50 by the pressure operated structure 54, say in an upward direction, an electric circuit will be closed through wire 46, contacts 58, 48' and solenoid 42. The closing of an electric circuit through the solenoid 42 will operate 40 and energize the motor 31, which will rotate the shaft 34 device 54. The energizing of motor through switch structure M will operate the differential gearing 56 to operate the shafts 3t and It and arcaaeo motors, operated directly or indirectly by pressure mechanisms, driving a shaft with cams mounted thereon which in turn operate cam switches energizing or deenergizing distributor 'valves, these same distributor valves may be controlled directly or indirectly by pressure responsive mechanisms which will make or break an electric circuit at a definite or adjustable pressure and reverse the action on a definite or adjustable change in pressure. Mechanical or electrical means may be provided to insure a proper time interval between steps thus preventing indecisive action of the distributor valves or a too frequent reversal of operation known as hunting.

In Fig. 19 is diagrammatically illustrated a system of control for variable capacity compressors such as outlined in the preceding paragraph wherein the distributor valves are controlled indirectly by pressure responsive mechanisms which make or break an electric circuit at a definite pressure and control the opening and closing of the distributor valves electrically through relay switch structures.

In this modified form of construction the low pressure cylinder A and the high pressure cylinder B of the compressor are arranged to permit loading and unloading of the cylinders in various percentages of their capacity in exactly the same manner as are the compressor cylinders I and 2 of the structure shown in Fig. 1 of the drawings. The solenoid operated distributor valve structures It, I02 and I03 are likewise the same as the structures I2, I5 and I7, and operate in the same manner to control the operation of the loading and unloading valves of a compressor.

In this modified construction, the energization of the solenoids I04 of the respective distributor valve structures is controlled by pressure switches H1, H2, H3 and H4, through relay switch structures H5, H6, H1 and II 8 in the manner hereinafter described. Both the pressure switch structures and the relay switch structures may be of any approved types which may be purchased on the open market. The relay switch structures are shown as comprising the switch blades I20 carried by the pivoted levers I2I. The magnetic co'ils I22 of the relays are energized to attract the levers I2I to move the switch blades I20 into closed position. Upon deenergization of the coils I22 the springs I23 will act to move the switch blades I20 into circuit breaking or open position.

In Fig. 19 the pressure fluid required for operating the pressure switches III, H2, H3 and H4 which control the loading and unloading of the compressor is delivered to the switches from a tank or receiver I24 which is in turn connected to a tank or receiver I25 by the connection I26. A valve I2'I is provided in the pipe or connection I26 for the purpose more fully hereinafter described. While in the drawings, the receiver I25 is indicated as receiving its pressure fluid from the discharge of the compressor, it is to be understood that the invention is equally applicable to systems'wherein the receiver I25 receives fluid under pressure which fluid is subsequently deliv ered to the suction of the compressor thereby permitting control of the loading and unloading of the compressor by the pressure of the fluid entering its suction.

In describing the operation of the modified construction shown in Fig. 19, assuming that the compressor unloading mechanism is attempting to maintain the pressure at approximately 100 pounds per square inch, when this desired pressure is reached the pressure switch I I I will open thus deenergizing the solenoid I04 of the distributor valve structure IOI, such deenergizing being effected through the relay valve structure H5. The deenergizing of the solenoid of the distributor valve IOI will operate the control valves C of the compressor cylinders A and B and the compressor willthen operate at, seventyfive percent of its capacity. If the pressure continues to rise or increase, the pressure switch I I2 will open and deenergize the solenoid operated distributor valve I02 through the relay valve I I6. The operating of the distributor valve structure I02 will open the control valve D'on the crank end of the compressor, thus permitting the compressor to operate at fifty percent of its capacity.

With a further increased pressure, the pressure switch II3 will operate, opening the switch and breaking the circuit through the coil I22 of the relay switch structure II8. When the circuit is broken through the coil I22 of the pressure switch IIB, the blade I20 of this pressure switch will break the circuit through the solenoid I04 of the distributor valve construction I03 and will close a circuit through the solenoid I04 of the distributor valve structure I 02, reenergizing this solenoid I04.

This operation gives the reverse step in the unloading cycle and closes or'renders ineffective the unloading valve structuresD at the crank end of the cylinders, opening those at the head end of the cylinders which together with the control valves C cause the compressor to operate at open or closed and will require a differential pressure still continues to increase the pressure switch II4 will open, deenerigizing the solenoid I02 through the relay 0, thus having all of the control valves open and causing the compressor to operate at zero capacity.

The pressure switches III to I I4 inclusive, may be of any approved conventional design, now on the market, arranged for snap action on definite changes in pressure, that is, they will be either open or closed and will require a diflerential'pressure before they will operate. They are shown in the drawings as closed and open for breaking the cifcuit upon a pressure differential. With the conventional type of pressure switches on the market they embody means whereby the pressure diflerential required for in the operation may be varied through adjustment features of the switches.

To provide a time delay or to provide a proper time interval between the various steps in the loading and unloading of the compressor, thus preventing indecisive action of the distributor valves or a too frequent reversal of operation, known as hunting, any suitable approved type of a time delay element may be provided. It may orifice for retarding the flow of the pressure fluid from the receiver I25 to the auxiliary receiver I24 so as to delay slightly the delivery of fluid under an increased pressure to the receiver I24 and consequently to the pressure switches III to H4. The valve I21, may be adjusted to regulate the widely modified within the invention defined by the claims.

What is claimed is:

1. A regulator" for fluid pressure systems and the like, comprising electro-responsive means and means actuated thereby for controlling the pressure of said system, means responsive to a predetermined value of pressure for energizing said electro-responsive means, means actuated by said electro-responsive means for changing the pressure response setting of said pressure responsive means, and means responsiveto said last-named means for restoring said pressure setting to its original value.

2. The combination with a variable capacity air or gas compressor, of control valves on said compressor for controlling the loading and unloading of the compressor, electrically operated means for controlling operation of said control valves, means responsive to deviation from a predetermined pressure for controlling operation of said electrically operated means, means for varying the setting of said responsive means, and means for restoring the original setting of said responsive means. v

3. The combination with a variable capacity air or gas compressor, of control valves on said compressor for controlling the loading and unloading of the compressor, solenoid operated distributor valves for controlling admission of operating pressure fluid to said control valves, solenoids for operating said distributor valves, means responsive to deviation from a predetermined pressure value for controlling energizing of said solenoids, means for varying the setting of said responsive means, and means for restoring the original setting of said responsive means.

4. The combination witha variable capacity air or gas compressor, of control valves on said compressor for controlling the loading and unloading of the compressor, electrically operated means for controlling operation of said control valves, means responsive to deviation from a predetermined pressure for controlling operation of said electrically operated means, means for varying the setting of said responsive means through a series of predetermined positions, and means for restoring the original setting of said responsive means by reversing its movement through the series of predetermined positions.

5, The combination with a variable capacity air or gas compressor, of pressure operated control valves on said compressor for controlling the loading and unloading of the compressor, electrically operated means for controlling operation of said control valves, means responsive to deviation from a predetermined pressure for controlling energizing of said electrically operated means,

said means including a master switch, means for varying the setting of said master switch, means for restoring the original setting of said switch, means for operating saidswitch setting means, and means operated by said switch setting means for controlling operation thereof.

6. The combination with a variable capacity air or gas compressor, of pressure operated control valves on said compressor for controlling the loading and unloading of the compressor, solenoid operated distributing valves for controlling admission of operating pressure fluid to said control valves, means responsive to deviation from a predetermined pressure for controlling operation of said solenoid operated valves, said pressure responsive' mean including a master switch, means for varying the setting of said master switch, means for restoring the original setting of said switch, said responsive means including selective means for selectively actuating said solenoid valve, and means for controlling the time interval of operation of said selective means.

7. The combination with a variable capacity air orgas compressor, of pressure operated control valves on said compressor for controlling the loading and unloading of the compressor, solenoid operated distributor valves for controlling admission of operating pressure fluid to said control valves, means responsive to deviation from a predetermined pressure for controlling operation of said solenoid operated valves, said pressure responsive means including a master switch, means for varying the setting of said master switch, means for restoring the original setting of said switch, means 1:01 operating said switch setting means, means operated by said switch setting means for controlling operation thereof, said responsive means including selective means for selectively controlling energizing of said solenoid valves, and means for controlling the time interval of each operation of said selective means.

8. The combination with a variable capacity air or gas compressor, of pressure operated-control valves on said compressor for controlling the loading and unloading of the compressor, means for controlling operation of said control valves comprising means responsive to deviation from a predetermined pressure of fluid compressed, means for varying the setting of said responsive ment through the series of predetermined positions, means for restoring the original setting of said responsive means by reversing its move-' -ment through the series of predetermined positions, said setting means and said restoring mean embodying means whereby said responsive means may be moved to certain of said predetermined positions and restored to its original position without movement through the complete series of positions.

9. The combination with a variable capacity air or gas compressor, of control valves on said compressor for controlling the loading and unloading of the compressor, electrically operated means for controlling operation of said control valves, means responsive to deviation from a predetermined pressure for controlling energizing of said electrically operated means, said means including a master switch, means for varying the setting of said master switch, means for restoring the original setting of said switch, means. for operating said switch setting means, and means operated by said switch setting means for controlling operation thereof.

10. The combination with a variable capacity air or gas compressor, of control valves on said compressor for controlling the loading and unloading of the compressor, means for controlling operation of said control valves comprising means responsive to deviation from a predetermined pressure of fluid compressed, means'for varying the setting of said responsive means through a. series of predetermined positions, means for restoring the original setting of said responsive means by reversing its movement through the series of predetermined positions, said setting means and said restoring means embodying means whereby said responsive means may be moved to certain of said predetermined positions and restored to its original position without movement through the complete series of positions,

11. A fluid pressure control system comprising in combination a variable capacity fluid compressor having a plurality of valves for controlling the loading or unloading of the compressor, solenoids for operating said valves, rotary cams for controlling the energization of said solenoids and means controlled by pressure fluid for controlling rotation of said cams.

12. A control system for variable capacity fluid compressors and the like having a plurality of valves for controlling the loading and unloading of the compressor, a plurality of solenoids for controlling the operation of said valves, a master switch controlling the energization of said solenoids, means actuated by pressure of the compressed fluid for moving the elements of said master switch into circuit closing position and means independent of said pressure actuated means for moving the elements of said' switch out of circuit closing position.

13. In a control system for compressors and the like having a plurality of valves for controlling the loading and unloading of the compressor, a plurality of solenoids for operating said valves, a master switch for controlling the energization of said solenoids comprising a movable blade and a plurality-0f movable contacts, means actuated by pressure of the compressed fluid for.

Images