US2338451A

US2338451A - Compressor control

Info

Publication number: US2338451A
Application number: US422635A
Authority: US
Inventors: Jr William J Mccoy
Original assignee: Individual
Current assignee: Individual
Priority date: 1941-12-12
Filing date: 1941-12-12
Publication date: 1944-01-04
Anticipated expiration: 1961-01-04

Description

Jan. 4, 1944. w. J. McCoy. JR 2,338,451

COMPRESSOR CONTROL Filed Dee. 1:2,v 1941 4 sheetssneet 1 Tiri- IN NToR v Jan. 4, 1944.

W. J. MCCOY, JR. COMPRESSOR CONTROLv Filed Dec. l2, '1941 4 Sheets-Sheet 2 William LL McCoy, Jr., mvz-:N R

ATTORNEY Jan. 4, 1944. \w, J. McCoy, JR 2,338,451

COMPRESSOR coNTnoL- Filed Dec. 12, 1941 A 4 Sheets-Sheet 3 William J. M llnJr'.

INV NTOR ATTORNEY Jan. 4, I1944. w, J. mdf JR 2,338,451

COMPRESSOR vCONTROL Filed Dec. 12, 194]r 4 Sheets-Sheet 4 William -J. Mgy,.1r.,

INVENTO rATTORNEY y Patented Jan. 4, 1944 UNITED STATES PATENT' @FFME COMPRESSOR CONITBQL `William E. McCoy, Jr., Holyoke, Mass.

Application December 12, 194i, ,Sieiinll 422,635

(Cl. 230mm) 22 Claims.

This invention relates to air or gas compres.- sors, and more particularly to a, loading and unloading mechanism therefor.

An object of the vpresent invention is to provide a novel, relatively simple, and inexpensive mechanism of positiveaction which will eliminate all hunting or vasclllating action of the unloading mechanism and which is particularly adaptable for controlling the loading and unloading of a single or multiple cylinder compressor vemployed in a. refrigeration system or otherwise.

present invention is also adaptable for controlling the loading and unloading of a multistage variable capacity compressor in predetermined percentages of its capacity, such loading and unloading heine automatically controlled by temperature at the point being cooled, or by pressure ci 'the :duid compressed, in accordance with the load demands upon the compressor, thereby main'tain/ringV practically constant the suction pressure, receiver pressure, or temperature produced lov the system in which the compressor is incorporated.

itnother object of the present invention is to provide, in a compressor control system, a mul.-

ti-point. 'mechanism for controlling operation of the unloader 'oi the compressor, which provides individual control of cut-in and cut-out points for each separate step of Compressor loading and unloading, and whereby, upon slight variation in the load demand on thecompressor, an initial lstep towards operation of the unloader will be performed, and upon continuance of said varia.- tion of load demand for a short interval, the second or iinal step in the control will occur, which will complete the circuit 'through the unloader mechanism, resulting in unloading the compressor in the percentage of its capacity controlled by the unloader operated. In instances of a singie stage compressor, the compressor will be come pletely unloaded upon operation of the unloader. When the variance in the load-demand has been met or complied with, the control mechanism acts reversely in two steps, first providing the initial step, and after a short interval, in the event the load demand conditions remain the same, per,n forming the second step and completing the reverse operation of the unloading mechanism.

Thus, `any hunting" action occasioned by fluttering variation in the load demand Will be abspecied, adjustable means whereby the .device -is to provide a compressor control mechanism as specified in which the'adiustalnle means controlling the different degrees ci variation in load demand to which the loadingand unloading ci the compressor is responsive are constructed and arranged .to permit overlapping; oi the steps oi control or the compressor, so that the total range covered by vthe several steps is materially less than that required rwith the same differential in y each. step when operated in sequence without y thegloadiris and unloading cycle.

f With these and other objects in view, as may `appear from the accompanying specication, the invention consists oi various features oi construction and combination ci parts, which will be first described in connection with the accompanyinurl drawings, Ashowing a compressor control of the .preferred iormemhodying the invention, and the features forming the invention will be specically pointed out in .the claims.

inthe drawings:

Figure l is a planview of the improved compressor unloader control.

Figure 2 is a section on the line 2- 2 of Figure 1.

Figure 3 is a cross-section on the line 3-3 of Fig-ure 2.

eFigure .-4 is a diagrammatic view illustrating the compressorcontrol mechanism for controlling the loading and unloading of one cylinder of a compressor. v

Figure 5 is a diagrammatic view, partly in sec tion, showing a multiple control system for corrn trollingrstopping and starting, and loading and unloading, of ya `multi-stage, multiple cylinder compressor, .in various percentages ofthe capacity .of the compressor.

Figure .6 is a .diagrammatic view,.partlyin sec tion, or amodied form of control system for Referring more particularly to the drawings,

wherein the unloading governor or control mechanism per se is shown,in Figures 1 to 3, the

governor or control mechanism perse includes a suitable supporting casing or housing I, which has a contact carrying bar 2 rigidly secured thereto, on which a contact plate 3 is attached or supported. The supporting bar 2 is of insulating material.

A second, movable supporting bar 5, of insulating material, is movably supported from the bar 2 by means of the pivoted carrying elements 8. The bar 5 has a plurality of contact operating members 1 adjustably carried thereby, which are arranged in pairs or sets, eachv set comprising an on contact operating member 8 and an oiiI contact operating member 9. Any desired number of the adjustable contact operating members 1 may be provided, depending upon the number of circuits to be controlled, i. e., the number of steps of predetermined percentages of the capacity of 'the compressor in which the compressor is loaded or unloaded. l

The contact operating members 1 cooperate with spring contacts III, which are likewise arranged in pairs, constituting an on contact II and an off contact I2. The contacts I are carried by a. bar I4, of suitable'insulating material, and they are connected in the electrical circuit controlling the loading and unloading of a compressor, as will be hereinafter more specincally referred to in connection with. Figures 4, and 6 of the drawings.

The bar 5, and consequently the contact operating members 1, are moved in response to pressure or load demand variations, by means of a bar I6, which is pivotally connected, as shown at I1, to the arm I8 of a bell-crank I3. The arm 20 of the bell-crank I9 is engaged and operated by the contactoperating member 2| or a pressure actuated structure 22. This pressure actuated structure 22 may be of any approved type, which may be purchased upon the open market, and its specinc construction forms no part oi the present invention. The action of the pressure actuated member 22 is opposed by a spring 23, which is connected to the arm I8 and anchored to the casing I in any suitable manner, as by the adjusting screw 24. A suitable mechanism 25 is provided for adjusting the tension of the spring 23.

`Adjustment of the mechanism 25 to vary the tension of the spring 23 determines the control point at which the loaddemandmpon the compressor will actuate the bar 5 and consequently effect a loading or unloading step on the compressor, and it maybe regulated independently of 'adjustment of the operating member 1.

In the diagrammatic illustration in Figure 4 of the drawings the improved compressor unloading mechanism or control is shown as applied to a single stage compressor, preferably of the type used in refrigeration, wherein the loading and unloading of the compressor, as indicated at A, is a single step operation, i. e.,a stop and start unloader.

When vthe pressure in the'system associated with the compressor A falls, increasing the load demand on the compressor, the pressure element 22 will be operated or collapsed, which will permember 22 further collapses or recedes, permitting the spring 23 to move the movable bar l 4 another step, which moves the contact operating element 8 a sufficient distance to permit the on" contact II to engage the contact strip or bar 3.

The contact II is connected to one pole, namely the pole 29, of an electrical relay 38, of approved construction, while the contact I2 is connected to the contact 3| of the contact relay. The contact II is also connected to one pole of the solenoid coil 32 or the relay 30. so that when the contact II engages the bar 3 a circuit will be closed through the solenoid coil 32, 'which will act-upon the movable circuit closing element 33 of the relay 30, moving it into engagement with the contacts 29'and3l. At the same time that the circuit is closed through the contacts 29 and 3I, the movable element 33 will close the circuit through the contacts 34 and 35, and consequently through the solenoid structure 38 oi the distributor valve structure 31.` The operation or the'distributor valve structure 31 will control delivery oi' actuating pressure fluid to the unloading mechanism 38 of the compressor A, permitting operation of the unloading mechanism 38 to unload the oompressor.

Any suitable type of unloading mechanism may be provided for use on the compressor A without departing from the spirit of the present invention, and the drawings (Figure 4) show one ofn many conventional. types oi unloader mechanism.

The unie-ader mechanism in Figure 4 comprises a pressure actuated piston 38 which, when pressure is delivered against the `piston through the three-way distributor valve structure 31, will be actuated to hold open the suction valve 40 of the compressor, to unload the compressor. When it is desired to ioad the compressor, the distribuitor valve 31 is operated to permit the bleeding of pressure fluid from the unloader mechanism 38, which will relieve the suction valve 40 of the compressor and permit it to act in its usual manner. It is to be understood, of course, that presvsure iluid for actuating the unloader 38 may be derived from any suitable source (not shown);

When the pressure builds up in the system with which the compressor A is associated, this pressure, acting upon the pressure element 22,

operates it to move the bell-crank I9 against the tension of the spring 23. The first step of such action results in the moving of the contact II out of engagement with the contact bar 3. The circuit through the relay 30, however, is held through the oi contact I2, so that the solenoid as of the distributor valve a1, and the 11stributor valve 31, remain in their positions to v load the compressor. As the pressure in the line builds up further, the gradual expansion of the pressure element 22 operates the bell-crank farther, which moves the oiI contact I2 out of engagement with the bar 3 and completely breaks the circuit through the relay 3IIy and solenoid 38, permitting actuation of the valve 31 to loadlthe compressor. v 'Y aeeaam The degree lof length oftime of theholdover action of the governor may be controlled by variationin adjustment of the contact op- The energizing and de-energizing of the solenoids 50, E5 and 64, and consequently the

conerating members

8 and 9, and likewise the ncrements in which the compressor is unloaded may be varied by adjustment of these

contact operating members

8 and 5.

In Figure 4 of the drawings the circuit is shown as being a temperature controlled circuit. That is, the pressure actuated eiement 22 is operated by a thermal element 45 of any approved type, which may be purchased upon the open market, and thus this system shown in Figure 4 is particularly adaptable for use in refrigerating systems.

In Figure 5- of the drawings a multiple control for a multiple cylinder compressor used in a reirigerating system is shown. In such systems it is usual to use a thermostatic control, which is actuated by the temperature of the medium being cooled, as the primary control for the loading and unloading mechanism. In some such installations the compressor loading is controlled from suction pressure. When the -suction pressure or the cooled medium temperaturer falls, the load on the compressor is decreasing and it is necessary to unload the compressor or compressors in steps corresponding to the falling of the suction pressure or temperature -of `this medium being cooled. Should the load decrease sufficiently, that is, below a predetermined point, the structure shown in Figure 5 of the drawings shuts down or stops the compressor, consequently stopping refrigeration. II"hen, when the temperature of the medium being cooled rises, with a resultant rise in the suction pressure, causing a load in-V piston 56, which'operates the mechanism 51, y

which in turn controls operation of the suction valve 58 for controlling the loading and unloading of the cylinder of the multi-cylinder compresser structure. The delivery of actuating pressure fluid to the pressure actuated unloading mechanism 53 is controlled by a three-way valve S2, which is actuated by a solenoid 64, while the delivery of actuating pressure to the unloading mechanisms 54 and `55 of the cylinders 5I and 52 is controlled by three-way valves 5l and 59. The pressure fluid employed for actuating the .unloading mechanisms 53, 54 and 55.may be derived from any suitable supply source (not shown), suchas from the discharge manifold of the compressor system, and it is fed to the various three-way valves 59, El and 52 through the inlet pipe 55. From said valves it is delivered to the unloading mechanisms through the

respective pipes

66, 61 and 58. These

pipes

55, 51 and 63 also serve as return pipes 'for the actuating pressurefluid to permit it to bleed from thel various unloading mechanisms, through the respective three-way valves, 'and out through the outlet 59, which may deliver it to any suitable point, or to the suction manifold of the system (not shown).

trol of the loading and unloading of the rvarious compressor cylinders, is in turn controlled by .the governor or control mechanism 1c, which is which engage the

movable contacts

18 and 19,'f`respectively, for moving these contacts out of engagement with the contact bar 80, or permitting them to move into engagement with the contact bar 80, to make orbreak a circuit through the electrical relay 8|, and consequently through the respective solenoid whichv is connected in circuit with the individual unit. As, for example, the unit 1l is connected in circuit with the source of electrical supply and the solenoid E4, so that the unit 1I will ycontrol operation of the solenoid 64, the Vthree-way valve 62, and the unloading mechanism 53, for controlling the loading and unloading of the compressor cylinder 59. Likewise, the unit i2 is connected in circuit with the source of electrical supply, the solenoid 63, valve 5I, and unloading mechanism 51S for controlling the loading and unloading of the compressor 5l. The unit 13 is connected in circuit with the source of electrical current supply, and with the solenoid 60, for actuating the three-way valve 59 to control operation of the unloading mechanism 55, which controls the loading and unloading of the compressor cylinder 52.

While in the diagrammatic Figure 5 the units 1l, 1.2, 13 and 14 are shown as individual units. this illustration is ofcourse diagrammatic, and merely for the purpose of more clearly illustratu ing vthe invention. 'In actual practice and construction, the multi-point controler governor 10 shown in Figure` 5 will be constructed the

same actuating members

8 and 9, corresponding to thev

members

16 and 11 shown in Figure 5. A pair of such actuating members is provided for each of the solenoids and for'the stop and start control of the compressor, controlled by the unit 14 in Figure 5. The operation of the governor 1 5 is identical with the operation hereinabove described. The bar 15 is moved to make or break electrical circuits through the respective solenoids, etc., by the operation of the pressure actuated member 22', which is in turn actuated by a thermal device 82. The pressure actuated member 22 operates a lever l5 which moves the bar 15. The sequence of energizing or de-energizing of the solenoids is controlled by the adjustment settings of the

respective actuating members

16 and 11, so that the various three-Way valves will be actuated in the desired or predetermined sequence, dependent upon the respective settings ci said actuating members.

In the `construction shown in Figure 5 of the drawings, the last unit, 14, in the series of units, and consequently the lastone operated 'in the unloading sequence, and the nrst one operated in the loading sequence, is Aconnected in circuit, through the electrical-relay 84, with the switch structure 85, which controls the stopping and starting of the electrical motor 06 0i the compressor. Thus, when the

contacts

18 and 19 of the unit 14 are actuated, they will make or breakthe circuit to the motor 86 to stop or start the compressor. A hand switch 01 may beconnect ed in the circuit between the source of electrical supply and the various solenoids 60. 63 and 0I to to permit manual cutting in or cutting out of the system. i

Figure 6 shows a multi-stage control for controlling the loading and unloading of a compres- Asor in a plurality of predetermined percentages of its capacity. In this view a multiple cylinder compressor is shown in which the ilrst step of unloading is by operation of the unloading mechanisms 90, which open the crank ends of the compressor cylinders 9| and 92 to clearance pockets 93 and 94. The second step in unloading is the closing of the crank ends of the compressor cylinders to the clearance pockets, and the opening or operation of the suction valves 95 of the head ends of the cylinders, to permit the unloading of the head ends of the cylinders. For complete unloading of the compressor, the suction valves 96 at the crank ends o f the cylinders are held open, thus allowing the compressor to by-pass from crank end to suction end and operate completely unloaded. 'I'he unloading valves The energizing of the solenoids 90, and |02,

I and consequently the operation of the distributor valves 91, 99 and |0|, is controlled by a multipoint control mechanism such as is shown in Figures 1 to 3 of the drawings.

In this Figure 6 of the drawings, the control mechanism, generically indicated by the numeral I 03, is shown diagrammatically, for purposes of illustration, but itis to be understood that it would be constructed in accordance with Figures 1 to 3 of the drawings, and the various steps in the loading and unloading operations of the compressor structure would be controlled and timed by the setting of the contact actuating members |04 and |05 in each of the respective units of the multi-point control mechanism |03. The various units |06, |01 and |08 of the control mechanism |03 are identical in construction with the units of the control or governor shown in Figure 5, and with the structures shown in Figures 1 to 4 of the drawings. Each unit comprises a pair of contact actuating members |09 which are carried by the bar H0. The bar ||0 corresponds to the bar S ,shown in Figures 1 to 3 of the drawings,

land the actuating mem-bers |09 in each set or unit are adjusted to provide any desired sequence in,

the loading and unloading operations of the compressor. By incorporating the proper num-ber of normally opened and normally closed contacts on the relays, practically any unloading combina--` tion of the compressor may be had, such as providing single operation of the clearance pockets,

'combined operation of the clearance pockets and suction unloaders, or individual operation o! the suction unloaders to provide lfor operation oi the compressor in any oi! the numerous increments of its capacity.

In the construction shown in Figure 6 o! the drawings, the' bar III is actuated through the medium of the leverage or link structure ||2, by the pressure actuated member Ill. This pres- .sure actuated member Ill is preferably connected to the discharge (not shown) of the compressor structure so that the loading and unloading of the compressor will be controlled by variations in theA load demand upon the compressor occasioned by the use' of the iluid compressed. In all other respects this system shown diagram-v matically in Figure 6 operates identically with the structure shown in Figures 1'to 3170i the drawings and heretofore described.

It will be understood that the invention isnot to be limited to the specific construction or arrangement of parts shown, but that they may be widely modiiied within the invention defined by the claims.

What is claimed is:

1. The combination with an air or gas compressor, of control valvesior controlling the loading and unloading of the compressor in steps of' ergizing of said electrically operated means, said circuit closing means embodying a pair of actuating members for each step of unloading, said actuating members operable in sequence of predetermined intervals for providing delay in energizing or de-energizing of said electrically operated means, and means operated by variances in the load demand on the compressor for operating said actuating members.

2. The combination with an air or gas compressor, of control valves for controlling the loading and unloading of the compressor in steps of fractional parts of its full capacity,l electrically operated means for controlling operation of said valves, circuit closing means controlling the energizing of said electrically operated means, said circuit closing means embodying a pair of actuating members for each step of unloading, said actuating members operable in sequence oi predetermined intervals for providing delay in energizing or de-energizing of said electrically operated means, said actuating members being adjustable to vary the delay interval between the successive operation of the actuating members in each pair.

3. 'I'he combination with an air or gas compressor, of control valves for controlling the loading and unloading of the compressor in steps of fractional parts of its full capacity, electrically operated means for controlling operation of said valves, circuit closing means controlling the en ergizing of said electrically operated means, said circuit closing means embodying a pair of actuating members for each step of unloading, said actuating members operable in sequence of predetermined intervals for providing delay in energizing or de-energizing of said electrically oper ated means, means operated by variances in the load demand on the compressor for operating said actuating members, said actuating members being adjustable to regulate the degree of variance in load demand on the compressor required for each step of loading and unloading of th compressor.

4. The combination with an air or gas ,coms

aeaaeei gizing or de-energizing of said electrically operi ated means, means operated by variances in the load demand on the compressor for operating said actuating members, said actuating members of each pair being independently adjustable to vary the delay interval between the successive roperation of the actuating members in each pair and lalso being adjustable to regulate the degree of variance in load demand on the compressor required for each step of loading and unloading of the compressor.

5. The combination with an air or gas compressor, of control valves for controlling the loading and unloading of the compressor in steps of fractional parts of its full capacity, electrically operated means for controlling operation of said valves, circuit closing means controlling the energizing of said electrically operated means, said circuit closing means embodying a pair of actuating members for each step of unloading, said actuating members operable in sequence of predetermined' intervals for providing delay'in energizing or de-energizing of said electrically operated means, means operated by variances in the load demand on the compressor for operating said actuating members, said actuating members being independently adjustable to vary the delay .interval between the successive operation of the actuating members in each pair, and means adjustable independently of said actuating members to regulate the degree of variance in load demand on the compressor required for actuatingv said actuating members.

6. The combination with an air or gas compressor, of means for loading and unloading said compressor, electrically operated means controlling operation of said loading and unloading means, circuit closing means for controlling energizingof said electrical means, said circuit closing means embodying a pair of movable contacts, and contact actuating members operated by variances in the load demand on the compressor for moving said contacts, said actuating `members moving said contacts in sequence and arranged whereby a predetermined time delay will be occasioned between the successive movement of the contacts occasioning a delay in theoperation of the electrically operated means after the initial impulse of load variation on the compressor.

7. The combination with an 4air or gas ccmpressor, of means for loading and unloading said compressor, electrically operated means controltial impulse of load variation on the compressor, said actuating members being. adjustable to vary the delay interval between the successivevmovements of the actuating members. f

8. The combination with an air or gas compressor, of means for loading and unloading said. compressor, electricallyy operated means controlling operation of said loading and unloading means, circuit closing means for controlling'energizing of said electrical means, said circuit closing means embodying a pair of movable conltacts, contact actuating members operated by variances in the load demand on the compressor for moving said contacts, said actuating members moving said contacts in sequence and arranged whereby a predetermined time delay will be occasioned between the successive *movements of the contacts occasioning a delay in the operation of the electrically operated means after the in-v itial impulse of load'variation on the compressor, said actuating members being adjustable to regulate the degree ofvvariance in load demand on the compressor required for each step ,of loading or unloadingoi the compressor. f

9. The combination with an air or gas compressor, of means forloading and unloading said compressor, electrically operated means controlling operation of said loading and unloading means, circuit closing means for controlling energizing oi said electrical means, said circuit closing means embodying a pair of movable contacts, contact actuating members operated by variances in the load demand on. the compressor for moving said contacts, said actuating membersl moving said contacts in sequence and arranged whereby a predetermined time delay will be oc'-- casioned between the successive movements oi the contacts occaslonin-g adelay in the operation ling operation of said loading and unloading of the electrically operated means after the initial impulse of load variation on the compressor, said actuating members being adjustable to regulate the degree of variance in load demand on the compressor required for each step of loading or unloading of the compressonandy means adjustable independently of said actuating members to regulate the degree of Variance in load demand on the compressor required for actuating said actuating members, y

10. The combination with an air or gas compressor, of means for loading and unloadingsaid compressor, electrically operated meanscontrolling operation of said. loading and unloadingr means, circuit closing means for controlling energizing of said electrical means, said circuit closingmeans comprising a pair of movable. contacts connected in the circuit of said electrically operatedmeans so that both must be operated to make or break the circuit to the electrically operated means, and an independent actuating member for eachrof said contacts, said actuating members arranged to provide a time interval between the successive movements of the contacts, and means actuated by variance in tacts connected in the circuit of said electrically operated means so that both must be operated to make or break the circuit to the electrica1lyoperated means, an independent actuating mem'- ber foreach of said contacts,.said actuating -memberst arranged to provide a time interval tacts connected in the circuit of said electrically -operated means so that both must be operated to make or break the circuit to the electrically operated means, an independent actuating member for each of said contacts, said actuating members arranged to prov-ide a time interval between the successive movements of the contacts,

means actuated by variance in the load demand on the compressor for operating said actuating members, and said actuating members being adjustable to regulate the degree of variance in load demand on the compressor required for each step of loading or unloading of the compressor.

13. The combination with an air or gas compressor, of means for loading and unloading said compressor, electrically operatedmeans controlling operation of said loading and unloading means, circuit closing means for 4controlling energizing of said electrical means, said circuit closing means comprising a pair of movable contacts 'connected in the circuit of said electrically operated means so that both must be operated to make or break the circuit to the electrically operated means, an independent actuating member for each of said contacts, said actuating 'members arranged to provide a time interval between the successive movements of the contacts, means actuated by variance in the load demand on the compressor for operating said actuating members, said actuating members being adjustable independently `for varying the length of said time interval, and means adjustable independently of said actuating members to reguated by variances in load demand on the com-' pressor for moving said movable bar, and actuating members carried by said bar for moving said movable contacts.

15. The combination with an air or gas compressor, of means for loading and unloading said compressor, electrically operated means controlling operation of said loading and unloading means, circuit closing means for controlling energizing oi.' said electrical means', said circuit closing means including a stationary contact bar, a pair of movable contacts, a movable bar, means operated by variances in load demand on the compressor for moving said movable bar, and actuating members carried by said bar for moving said movable contacts, said actuating members being' adjustable relative to said bar for varying the degree of variance in load demand on the compressor required to move the contacts.

16. The combination with an air or gas compressor, of means for loading and unloading said compressor, electrically operated means controlling operation or said loading and unloading means, circuit closing means for controlling energizing of said electrical means, said circuit closing means including a stationary contact bar, a pair of movable contacts, a movable bar, means operated by variances in load demand on the compressor for moving said movable bar, and actuating members carried by said bar for moving said movable contacts, said actuating members being adjustable relative to each other to provide a variable time delayk between the movement of the contacts.

pressor, of means for loading and unloading said compressor, electrically operated means controlling operation of' 'said loading and unloading means, circuit closing means for controlling energizing of said electrical means, said circuit closing means including a stationary contact bar, a pair of movable contacts, a movable bar, means operated by variances in load demand on the compressor for moving said movable bar, actuating members carried by said bar for moving said movable contacts, said actuating members being adinstable relative to each other to provide a variable time delay between the movement oi' the contacts, and means applying restraining pressure on said means which is operated by variances in the load demand.

18. The combination with'an air or gas compressor, of means for loading and unloading said compressor, electrically operated means controlling operation of said loading and unloading means, circuit closing means for controlling energizing of said electrical means, said circuit closing means including a stationary contact bar, a pair of movable contacts, a movable bar, means operated by variances in load demand on the compressor for moving said movable bar, actuating members carried by said bar for moving said movable contacts, said actuating members being adjustable relative to each other to provide a variable time delay between the movement oi the contacts, means applying restraining pressure on said means which is operated by variances in the load demand, and means for varying the restraining pressure applied to said load-demand variance-operated means to regulate the degree of variance in load demand required to move said bar.

19. The combination with an air or gas `compressor, of means for loading and unloading said compressor, electrically operated means control' ling operation of said mst-mentioned means, an electric circuit including circuit closing means for controlling energization and de-energization of the respective electrically operated means, and means operated by variance in the load demand on the compressor for actuating said circuit closing means, the respective circuit closing means being so constructed and arranged as to operate with a delayed action after initiation' of either their circuit opening or closing operations.

20. The combination with an air or gas compressor, of means for loading and unloading said compressor, electrically operated means controlling woperation of said rst mentioned means, an electric circuit including circuit closing means for controlling energization and de-energization of said electrically operated means, and means operated by variance in the load demand on the compressor for actuating said circuit closing means, saidl circuit closing means being so construclted and arrangedas to operate with a delayed action after initiation of either the circuit opening or closing operation.

21.I The combination with an air or gas compressor, of means for loading and unloading the compressor, electrically operated means for controlling the operation of said first-mentioned means, an electric circuit .including circuit closing means for controlling energization and deener-gization of the respective electrically operated meanasaid circuit closing means comprising a iirst contact connected in said circuit, a. pair of movably mounted contacts for each of said electrically operated means and connected in said circuit for co-action with said first contact, adjusting means for the respective movably mounted contacts for adjusting the same relatively. to each other in each pair or each pair relatively to the other pairs and with respect to said first contact, and means operated by variance in load demand on the compressor for shifting said movably mounted contacts relatively to said nrst contact.

22. The combination with an air or gas compressor, of means for loading and unloading the compressor, electrically operated means for controlling the operation of said mst-mentioned means, an electric circuit including circuit closing means for controlling energization and deenergization of the respective electrically operated means, said circuit closing means comprising a rst contact connected in said circuit, al support, a pair of fiexible contacts for each of said electrically operated means and connected in said circuit for co-action with said rst contact, said flexible contacts being carried by said support, a carrier means mounted for movement relatively to said rst contact and providedy with adjusting screws for the respective flexible contacts for adjusting the latter relatively to each other in each pair or each pair relatively to the other pairs and Awith respect to said rst contact, and means operated by variance in load demand on the compressor for shifting said carrier means and said adjusting screws relatively to said exiblc contacts for shifting the latter relatively to said first contact.

WILLIAM J. MCCOY', JR.V l