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Publication numberUS2312728 A
Publication typeGrant
Publication dateMar 2, 1943
Filing dateJul 12, 1941
Priority dateJul 12, 1941
Publication numberUS 2312728 A, US 2312728A, US-A-2312728, US2312728 A, US2312728A
InventorsJohnston Allan T, O'hagan Bernard E
Original AssigneeUnion Switch & Signal Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Compressor control system
US 2312728 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

March 2,1943. B. E. @HAGAN HAL, 2,312,728

` vCOMPRESSOR CONTROL SYSTEM Filed July 12, 1941 "2 Sheets-Sheet l R5 alzand THE/I2 ATTORNEY Nw. .WN WN 4..

im u March 2, 1943.

B. E. OHAGAN ET AL COMPRESSOR CONTROL SYSTEM Filed .July 12,v 1941 2 Sheets-Sheet 2 INVENToRs and Patented Mar. 2, 1943 COMPRESSOR CONTROL SYSTEM Application July 12, 1941, Serial No. 402,178

7 Claims.

Our invention relates to improved means for controlling a plurality of -air compressors.

In some situations, as for example in interlocking plants where pneumatic switches are employed, several air compressors are provided to supply the compressed air to operate the switches. These compressors are driven by electric motors which are supplied with current over the same transmission line while they supply compressed air to the same or connected'reservoirs. These compressors are controlled by pressure switches so that they are placed in operation when the pressure in the reservoir drops to a predetermined value, and are continued in operation until the pressure in the reservoirs is increased to a higher predetermined value.

It is desirable in situations of this kind that on a reduction in the pressure in the reservoir that all of the air compressors driven by mo-y tors supplied with energy through the same transformer do not attempt to start up simultaneously as this might place such a heavy load on the transformer that the voltage of the current supplied through the transformer would drop so much that the motors would be unable to start the compressors.

It is desirable also that the compressors be unloaded when they are started, that is, that they be not required to compress air against the pressure in the reservoir during the period in which the compressors are being started.

It is an object of our invention to provide improved means for controlling a plurality of air compressors so that there is a time interval between the start of operation of the compressors.

A further object of the invention is to provide a system of the type described and incorporating means to maintain each of the com-V pressors unloaded during the starting period of the compressor.

Another object of the invention is to provide a system of the type described and which employs standard commercial apparatus insofar as 4 5l possible.

Other objects of the invention and'features of novelty will be apparent from the following description taken in connection with the accompanying drawings. Y

We shall describe two forms of compressor control systems embodying our invention, and' shall' then point out the novell features thereof in claims.

ing the compressorcontrol system provided by our invention applied to two compressors and Fig. 2 is a diagram showing the compressor control system of our invention applied to two compressor units each having two compressors.

Similar reference characters refer to similar parts in each of the two views.

Referring to Fig. 1 of the drawings, there is shown therein a compressor control system embodying our invention. The equipment shown in Fig. 1 includes compressors CI and C2 which are driven by alternating current motors MI and M2, respectively. The compressors Cl andv C2 may be of any construction well known in` the art and are of a type which do not incorporate-unloading means. The motors Ml and M2 may be any appropriate type of alternating current motors.'

The compressors Cl and C2 supply fluid under pressure or compressed air to a reservoir R from which air may be drawn for any desired purpose, as for example to operate the track switches in an interlocking plant on a railroad.

The compressor Cl is connected to the reservoir R through a supply pipe and a check valve Vi which permits air to be supplied from the compressor to the reservoir and prevents flow of air from the reservoir to the compressor. The compressor C2 is connected to the reservoir R through a check valve V2, the supply pipe, and also through the check valve Vl so that air may be supplied from the compressorV C2 through the check valves V2 and Vl to the reservoir R., but is prevented from flowing from the reservoir to the compressor. The check valve V2 also preventsair compressed by the compressor CI reaching the compressor C2.

An unloading volume WI is connected to thesupply pipe intermediate the compressor CI and the check valve VI, while a similar unloading volume-W2 is connected intermediate the compressor C2 and the valve V2.

Pressure operated switches P art and their design is not a part of our inven-` tion. These switches include contacts which are governed in accordance with thepressure in the reservoir. These contacts are closed when the air in the reservoir `is at atmospheric pressure and. remain closed until the pressure in the reservoir is increased to a predetermined value when they l Vbecome opened. These contacts whenv open re- In the drawings, Fig. l is a diagram show- -main open until the pressure in the reservoir;

Iv and P2 are prof vided and are connected with the reservoir R. These switches lmay be of.

drops to a value somewhat less than that which caused them to open. The pressure operated switches also include means by which the pressures at which their contacts close and open may be adjustably varied as desired, and it is contemplated that the switches PI and P2 in this system will be adjusted to operate at dilerent pressures. The switch PI may be adjusted so lthat its contacts open when the reservoir pressure is '70 pounds and to close when it is 55 pounds to the square inch. The switch P2 may be adjusted so that its contacts open when the reservoir pressure is 60 pounds and to close when the pressure falls to 45 pounds.

The pressure switch PI has incorpora-ted therein an unloading valve device B which controls connection from the supply pipe andi thereby from the compressors CI and C2 to ,the atmosphere. The valve B is connected to the supply pipe intermediate the compressor CI and the check valve VI, and intermediate the check valves V2 and VI so that when the Valve B is open the compressors C I and C2 and the unloading volumes WI and W2 are vented to the atmosphere, while the check valve VI prevents escape of air from the reservoir R through the valveA B.

The valve B is controlled bythe pressure switch PI so as to be open when the contacts ofthe pressure switch are open, and to be closed when the switch contacts are closed.

A safety valve D is provided. and operatesY in the usual manner to release uid from the reser- Voir R if the Apressure therein exceeds a predetermined pressure.

The: current for operating the motors MI and M2 is supplied through a transformer T from a suitable source of alternating current the terminals of which are designated BX and CX. This energy may be supplied overa transmission line, not shown.

The supply of energy from the transformer T to the motors MI and M2 is' controlled by magnetic switches indicated generally by the reference characters SI and S2, while a thermal time delay switch Q is employed to provide a time interval between the supply of energy to the motors MI and M2. In addition, the magnetic switches SI yand S2 each incorporate a thermal overload device to protect the motor controlled by the switch in the event of an overload'.

The switches SI and S2 are providedwith manually operable control levers designated LI and L2, respectively. Each of these levers has an intermediate or oil position designated- O, in which it interrupts the circuit-of the winding of the associated switch to thereby prevent operation of the motor governed by that switch. Each control lever also has an automatic position A in which the circuit of the winding of the associated switch is controlled by the pressure switches in the manner hereinafter explained in detail. In addition, each of the control levers has a hand position H in which a circuit independent of the pressure switches ris established to energize the windingv of the associated switch and thereby cause operation of the associated compressor regardless of the pressure in the reservoir R.

The equipment is shown in Fig. 1 of the drawings in the condition which it assumes when, the pressure in the reservoir R: is above 55- pounds to the square inch so. that contact. IIL of pressure switch Pl and contact. Il of pressure switch P2 are open.Y The equipment is also shown with the vswitch SI interrupts connection from supply wire 2.9 leading from the other terminal of the transformer secondary winding to wire 2| leading to the motor M'I.

Similarly, contact 24 of switch S2 interrupts connection from supply wire I2 to wire 25 leading to motor M2 and contact 26 interrupts connection from supply wire 2l) to wire 21 leading to motor M2.

Accordingly, the motors MI and M2 are not operating, while energy is not supplied to the heating element 30 of thermal relay Q even though contact 3f of switch S2 is closed, since contact I0 of pressure switch P-I is open.

In addition, at this time the unloading valve B is open so that the unloading volumes WI and W2 and the pipes connected therewith are open to the atmosphere.

When` the pressure in the reservoir R drops below 55 pounds, the contact I Il of pressure switch PI closes, while the unloading valve B also closes. When contact I U of switch PI is closed, energy is supplied from transformer T to the winding of switch SI over the circuit which is traced from one terminal of the transformer secondary winding over lsupply wire I2, contact lil of switch PI, wire I control lever LI, and' contact 33 of the thermal overload device incorporated in switch SI to one terminal of the winding of switch SI, while the other terminal of this winding is connected to supply wire 2U `and thus to the other terminal of the secondaryv winding of transformer T.

On energization of the winding` of switch SI its contacts I5 and I6 pick up and establish connection from the supply wires I2 and 20 to wires I8 and 2l leading to motor MI so that this motor operates and drives compressor Cl. The compressor CI will start readily as the unloading volume WI is at atmospheric pressure so there is no air pressure to oppose operation of the compressor. As the compressor is operated, the pressure of the air in the volume WI, the supply pipe, and the connected pipes builds up, and when it exceeds the pressure in the reservoir R, air llows through the check valve VI to the reservoii. The check valve V2 prevents air supplied from compressor CI at this time from reaching volume W2 and compressor C2 so that the compressor C2 is maintained unloaded. The volume WI is proportioned so that the pressure therein does not build up appreciably until the compressor has been operated several revolutions and reaches a substantial speed so that the motor MI will be able to continue to drive the compressor after it is subjected to load.

On closing of contact I8 of pressure switch PI energy is supplied to the heating element of thermal relay Q over the circuit which is traced from one terminal of the secondary winding of transformer T through supply wire I2, contact Ill of switch PI, wire I4, control lever LI, wire 36, and contact 3| of switch S2 to one terminal 0f the heating element 3i) of relay Q, while the other terminal of the element 30 is connected to supply wire 20jand thus to the other terminal of the transformer secondary winding. On the supply of energy to the element 3B is heats up, and after the expiration of a time interval long enough for the compressor CI to have substantially reached its full speed the element 30 is hot enough tocause contact 38 of device Q to close.

Contact 38 of device Q when closed establishes a pick-up circuit for the winding of switch S2. through wire I2, contact I of switch PI, wire I4, contact 38 of device Q, Wire 40, control lever L2, and contact 4I of the thermal overload device incorporated in switch S2 to one terminal of the winding of switch S2, while the other terminal of this Winding is connected by wire 20 to the transformer T. Energy, therefore, is supplied to the winding of switch S2 and the contacts of this switch pick up and its contact 42 establishes connection from wire I4 to wire 4i) to maintain the winding of switch S2 energized after opening of contact 38 of device Q. On picking up of the contacts of switch S2 its contact 3I interrupts the circuit traced above for supplying energy to the heating element 33 of device Q so that this element cools and its contact 38 opens.

In addition, on picking up of the contacts of switch S2 its contacts 24 and 26 establish connection from supply wires I2 and 23 to wires 25 and 21 leading to motor M2 so that the motor M2 operates and drives compressor C2. As pointed out above, the compressor C2 is uriloaded at this time so that it will start readily.

When the pressure in the reservoir R increases to 70 pounds, the contact I0 of switch PI opens and interrupts connection from wire I2 to wire I4 and thereby cuts 01T the supply of energy to the windings of switches SI and S2 so that the contacts of these switches release and interrupt the circuits of the compressor motors MI and M2. In addition, on release of switch S2 its. contact 42 interrupts the holding circuit for the switch winding, while its contact 3I closes to permit energy to be supplied to the heating element 30 of device Q. At this time the unloading valve B associated with pressure switch PI also is opened so that the air under pressure in the unloading volumes WI and W2 and in the supply pipe may escape to the atmosphere.

The control system provided by our invention is arranged so that if either motor is obstructed or overloaded, the thermal overload device inu corporated in the switch associated with that motor will interrupt the circuit of the switch winding so that the switch contacts will release and interrupt the supply of energy to the motor.

If, for example` motor MI is overloaded and draws unusually heavy current for an excessive period, the thermal element 35, which is connected in series with the motor MI will be heated to an abnormal degree with the result that contact 33 will open and interrupt the' vwinding so that the switch contacts will close and energy will again be supplied to the motor.

If the 'motor now operates freely, it will con- This circuit is traced from transformer T tinue to operate until stopped by operation oi the pressure switch PI or b-y manipulation of the control lever LI. If, however, the overload condition remains, the thermal element will again be heated and contact 33 will again interrupt the circuit of the switch winding so that the switch contacts will again release and interrupt the switch motor circuit. .This cycle will be repeated indefinitely until the motor starts and runs, or until operation of the motor is prevented by the pressure switch PI or the control lever LI.

In like manner the motor M2 is protected by the thermal overload device in the switch S2. This device has a heating element which is connected in series with the motor circuit and on occurrence of an overload this element heats up and causes contact il to open. Contact 4I is included in both the pick-up and stick circuits for the switch winding so that when this contact is open, the switch winding is deenergized and the switch contacts release and interrupt the switch motor circuit. In addition, on realese of vthe switch contacts contact 3I establishes the circuit to permit energy to be supplied to the heating element of the device Q. If control lever LI is in its automatic position and contact I0 of pressure switch PI is closed, energy will be supplied to thermal element 3i? and contact 38 of device Q will'close and establish the pick-up circuit for the winding of swit-ch S2 so that the contacts of this switch pick up and reestablish the circuit of the motor M2, and also establish the holding'circuit for the switch winding and interrupt the circuit of the heating element 3l) of device Q..

If the motor M2 starts and operates properly, it will continue to run until stopped by pressure switch PI or control lever L2, but if the overload condition still exists, thermal element 45 will again be overheated and conta-ct 4I will interrupt the circuit of the Switch winding, and this cycle will be repeated indefinitely until stopped by switchPI or control lever LI or L2.

The system provided by this invention `is arranged so that if desired either compressor may be started and run at any time regardless of the pressure in the reservoir R.

If it is desired to operate compressor CI, the control lever LI is moved to its position H to thereby establish a circuit independent of the pressure switch PI for energizing the winding of switch SI. This circuit is traced from supply wire I2 through control lever LI, and contact 33 of theoverload device to one terminal of the switch winding, while the other terminal of this winding is connected to supply wire 20. The switch contacts I5 and i6 therefore close and establish the circuit of the motor MI and this motorv -for the motor MI.

When control lever LI is in position H, energy is supplied to the heating element 33 of device Q Yover the circuit which is traced from supply wire I2 through control lever LI, wire 36, and contact3l of switch S2 to one terminal of element 30, while the other terminal vof` this element isA connected to supply wire 20. The element 30 thereupon heats up so that contact 33 closes. However, closure of contact 38 will not establish the pick-up circuit for the winding of switch S2 unless contact Hl of pressure switch Pl is closed and if at the same time control lever L2 is Ain its automatic position. If .at the time the control lever VLI .is moved to its `position H the control lever L2 is moved to its off position O, the pickup circuit for switch S2 will not be established and this switch will remain released so that compresser C2 will not be operated. This arrangement permits a serviceman to operate only the compressor Cl if` desired so that he can inspect it and determine its condition. This arrangement is also such that if the control lever L2 is left in the automatic position when lever LI is moved to its position H, the switch S2 will not beenergized until after the expiration ofthe time delay period determined by thermal switch Q. This prevents starting of the compressors CI vand C2 at the same time and prevents overloading of the transformer.

The compressor CZ may also be operated whenever desired without regard to the condition of pressure switch P2. When control lever L2 is moved to its hand position H, a circuit is established to energize the winding of switch S2. This circuit is traced from supply wire I2 through control lever L2, and contact 4I of the overload protective means to one terminal of the winding of switch S2, the other terminal of which is connected to supply wire 20. The contacts of switch S2, therefore, close and establish the circuit of the motor M2 so that compressor C2 operates. The heating element 45 of the overload protection means is included in the motor circuit, while contact M of this means is included in the circuit of the winding of switch S2 so that the motor M2 is provided with full overload protection.

When the control lever .L2 is in its position H, no circuit is established'to supply energy to the winding of switch Si and this switch remains released.

The pressure switch P2 controls a pick-up circuit for the winding of switch S2 so that the compressor C2 will be operated if for any reason the compressor is not placed in operation by switch P I, and the pressure in the reservoir R drops to 45 pounds to the square inch.

When the pressure in the reservoir drops t 45 pounds, contact Il of switch P2 closes and establishes a pick-up circuit for switch S2, assuming that lever L2 is in its automatic position. This circuit is traced from supply wire I2 through contact l l of switch P2, wire 4G, control lever L2, and contact it of the overload means to one terminal of the winding of switch S2, while the other terminal of this win-ding is connected to supply wire 2t. Accordingly, the contacts of switch S2 close and establish the circuit of motor M2 so that the compressor C2 operates. and supplies air to the reservoir R.

At this time the motor is provided with full overload protection, while it will be seen that on closing of the contact il of pressure switch P2 the pick-up circuit for switch S2 is complete without waiting for operation of the thermal time delay device Q. The compressor C2 is, therefore, placed in operation without delay on closing of the contact l i of switch P2. This is desirable as the pressure in the reservoir is at an abnormally low value and should be increased without delay.

The pressure switch P2 may be provided with a contact 4% which may control an indication circuit to provide an indication at a remote point in the event that the pressure in the reservoir falls to the value e'ective to close the contacts of pressure switch P2.

The system shown in Fig. 1 is intended for use where there are two compressors. In some situations two compressors are inadequate and one or more units each having two compressors are provided to give additional capacity. These other units are located at other points in the interlocking installation and the. reservoirs of the various units are connected together so that any unit may supply air throughout the entire installation.

In sucha situation it is desirable that the same pressure switch control all of the compressors so that they will all operate the same amount and the wear on them will be evenly distributed. Accordingly, the equipment at one location is arranged so that it controls not only the compressors at that location but also those at the other locations.

While all of the compressors are controlled by a single pressure switch, it is desired that the compressors at each location do not start simultaneously as this would overload the transformer through which energy is supplied to the motors for the compressors at that location. Accordingly, the control apparatus for the compressors at each location should be arranged so that there is a time interval between the time of starting of the compressors at that location. The compressors at different locations are supplied through different transformers so there is no need to providefor a delay in the starting of the compressors at different locations.

Equipment of this type is supplied in complete units which include a case in which are mounted the compressors, motors, pressure switches, magnetic switches, etc., all wired up and ready to operate. For manufacturing reasons it is desirable that the units for all locations, both controlling and controlled, be substantially the same so that the same equipment maybe employed for either type of location.

In Fig. 2 of the drawings the control system provided by our invention is shown applied to two units of the type described. One of these units is the controlling unit, and the other is the controlled unit. In the drawings the controlling unit is shown at the left and the controlled unit at the right. Although only one controlled unit is shown it should be understood that two or more such units may be employed if desired.

The equipment at each of the locations is similar to that at the other locations, and is similar also to the equipment shown in Fig. l. At each location there are two compressors which are connected through check valves to a reservoir, as explained in connection with Fig. 1, while the reservoirs at the various locations are connected by a pipe 50 from which air may be supplied to the switches or other air consuming devices. The electric current for the motors for driving the compressors is supplied over a transmission line, while a transformer is provided at each location for supplying energy from the high voltage transmission line to the motors.

'Io identify the equipment at the different locations, the reference characters for the equipment at the controlling station, that is the equipment at the left-hand side of the drawings, are followed by the suiix a, while the reference characters for the equipment at the controlled or subsidiary location, that is the equipment at the right-hand end of the drawings, are followed by the surlix b.

The control levers LI and L2 at the various stations serve to condition the equipment at'that location for local or remote control or to prevent operation of the equipment altogether. Each lever has a local position LO in which it conditions the equipment at that location to be controlled by the pressure switch at that location, and a remote position RE in which the equipment at that station is controlled by the pressure switch at another station. Each control lever also has an oli position O in which it maintains the compressors at that location idle.

In addition, each unit is provided with a connector 5I which may be connected between the local contacts LO and the remote contacts RE of the control levers. This connection is installed in the unit which is to serve as the controlling unit, but is removed from the units which are to serve as subsidiary or controlled units.

The pressure switches PIa and P2a at the controllocation are adjusted t operate at the same pressures as the switches in the system shown in Fig. l. Thus the switch PI opens when the reservoir pressure reaches 'I0 pounds and remains open until the pressure falls to 55 pounds whereupon it closes and remains closed until the pressure is built up to70 pounds. The switch P2a opens at 60 pounds and closes at Ll pounds. The pressure switch PIb at the subsidiary location is adjusted to operate at slightly different pressures than the switch Pla at the control location. Thus the switch PII) opens at 63 pounds or slightly before Pia while it closes at 57 pounds or slightly before Pia. The pressure switch P2bf may be adjusted to operate at the same pressures as switch P2a.

If there are subsidiary locations other than that shown, the switches corresponding to PIb are adjusted to operate at the same pressures as switch PIb, that is, before PIa operates.

, The equipment is shown in the condition it assumes when the pressure in the reservoirs Ra and Rb-exceeds 55 pounds. At this time, the contacts of the pressure switches are open, while the unloading valve devices Ba and Bb are open and connect the unloading voliunes to atmosphere. In addition at this time, the contacts of the switches' Sla, S2a, SIb, and S21) are released and interrupt the circuits of the compressor motors so that neither of the compressors is operating.

When the pressure in the air in the reservoirs Ra and Rb falls to 57 pounds, switch PIb closes and closes the associated unloading valve Bb to thereby cut oi communication from unloading volumes WIb and W2b to the atmosphere. At this time, contact I0 of switch PIb is closed, but it has no effect as control levers LI b and L2b are in their remote positions.

When the pressure of the air in the reservoirs Ra and Rb drops to 55 pounds, switch Pla closes and closes the associated unloading valve Ba. At this time, contact Ill of switch PIa closes and establishes the circuit of the winding of switch SIa, and also establishes the circuit to supply energy to the heating element 30 of time element device Qa. In addition, on picking up of contact I0 of switch Pla, energy is supplied to the windsupply wire I2, contact II) of switch PIa,'control lever Lla, contact 33 of the overload device, and winding of switch Sla. to supply wire 26 leading to the other terminal of the transformer. Accordingly, the contacts I5 and I6 close and 'establish the circuit to supply energy to the motor MIa so that this motor operates and drives compressor Clo. The compressor Cla is unloaded at this time as volume WIa `has been connected to the atmosphere so the compressor will start readily.

The circuit for supplying energy to the heating element 30 of device Qa is traced from supply wire l2, contact I0 of switch Pa, control lever LIb, heating element 30, and contact 42 of switch S2a to supply wire 2t. Accordingly, the element 39 heats up, and causes contact 38 to close, to establish a pick-up circuit for the winding of switch S211, while on picking up of the contacts of this switch contact i2 interrupts the circuit of heating element 39 and contact 3| establishes the holding circuit for the winding of switch S2a. The pick-up and holding circuits for switch S2a include the contact 4I of the overload protective device so that the motor M2a is fully protected. As a result of picking up of the contacts of switch 52a, the circuit of the motor M2a is complete and this motor drives compressor 02a. The compressor 02a is unloaded when it is started as volume W20. is at atmospheric pressure.

At the time contact Ii) of switch Pa closes, energy is supplied to the winding of switch Sib over the circuit which is traced from control wire I2 through contact `Ill of switch Pla, jumper 5I, control wire 55, control lever Lib, contact 33 of the overload device in switch SI b, and winding of switch SIb to supply wire 20' which is common to both locations. Accordingly, the winding of switch SIb is energized and the contacts` I5 and I6 of this switch close and establish the circuit to energize motor M I b from transformer Tb so that motor MIb drives compressorlCIb. This compressor is unloaded as volume WIb is at atmospheric pressure, while on operation of the compressor the pressure in this volume builds up promptly as unloading valve Bb is closed since switch PIb is assumed to be adjusted to close at a slightly higher pressure than switch Pla.

On closing of contact I0 of switch Pla, energy is also supplied over the control wires to heating element 30 of device Qb. The circuit for supplying energy to the element 3!) is traced from supply wire I2 over contact IEI of switch PIa, jumper 5I, control Wire 55, control lever L21), element 3U, and contact 42 of switch S2b to common supply wire 20. Element 30 thereupon heats up and causes Contact 38 to close and establish a pick-up circuit for supplying energy over the control wires 55 and 20 to the winding of switch S2b, while on picking up of the contacts of this switch, contact 42 interrupts the circuit of element 30, and contact 3l establishes the holding circuit to maintain switch S2b energized by current supplied over the control wires. In addition, on picking up of the contacts of switch S2b; its contacts 24 and 25 establish the circuit for supplying energy from the transformer Tb to the motor M2b, and this motor drives compressor C212. The compressor C2b is unloaded at this time as volume W2b is at atmospheric pressure so that the compressor starts readily.

From the foregoing, it will be seen that on closing of pressure switch PIa, energy is supplied Yto the switches Sla and Slb so that compressors CIa and CIb start at once, while energy is also supplied to the heating elements 30 of- Ytime -delay devices Qa and Qb so that after a period, these devices establish the circuits of the switches 52a and S2b and thereby cause the compresso-rs C211 and C2b to operate.

While the compressors Cia and CI b start simultaneously, this is not objectionable as the motors for driving them are supplied from different transformers and there is no danger of overloading the transformers. Similarly, the compressors CZa and C2b start at about the same time, but these are also supplied from different transformers. The transformers Ta and Tb are both supplied from the same transmission line, but the capacity of this line is such that it is not aifected materially by the load represented by two compressors starting at the same time.

Each of the motors is provided With complete overload protection as the contact of the overload device associated with the switch governing that motor is included in the circuit of the winding of that switch. Accordingly, if any motor is overloaded, the circuit of the switch controlling that motor will be interrupted and the switch will interrupt the supply of energy to the motor.

The overload protection for each motor is independent of that for the other motors and cutting off. of the supply of energy to one motor will not affect the others. The supply of energy over the control wires 2!! and 55 is entirely independent of the switches at the control location so that release of either of these switches does not affect the switches at the controlled or subsidiary location. Accordingly, if any motor is overloaded, its circuit will be interrupted, but the other motors will continue to operate in the normal manner.

When the pressure of the air in the reservoirs Ra, and Rb increases to 68 pounds, switch Pib opens and opens unloading valve Bb. Thisvalve has a relatively small port so that air escapes through it slowly. Accordingly, as compressors Clb or C2b continue to operate most of the air compressed by them will be supplied to reservoir Rb and only a limited amount will escape through the unloading valve Bb to the atmosphere.

1t is desired that valve Bb open while the compressors Clb and C2b are still operating to insure that the compressors will be unloaded when they cease to operate. Y

When the pressure in the reservoirs Ra and Rb increases to 70 pounds, the contact l 0 of pressure switch P l a opens, while unloading valve Ba opens. Opening of contact I of switch Pla cuts 01T the supply of energy to the windings of switches Sla, SIb, S2a and SZbso that the contacts of these switches release and cut off the supply of energy to the motors so that they cease to operate.

As a result of opening of unloading valve Ba, the air in the unloading volumes Wla and W2a escapes to the atmosphere, While on cessation of operation of the compressors Clb and C2b, the air in the volumes Wl b and WZb escapes to atmosphere through the unloading valve Bb. Because of the restricted size of the port in this valve, some time is required for these volumes to reduce to atmospheric pressure, but they have ample time to do so before the compressors operate again.

In this modification ofthe invention, the pressure switches P2a and B2b serve only to control indication circuits to provide an indication if the pressure in the reservoirs falls substantially below that to which the switch Pla is intended to respond.

If it is desired to change the units so that. the

unit attire right becomes the controlli-ng unit and 775 that at the left becomes the controlled or sub-v sidiary unit, the jumper 5l is removed from the left unit andl is installed in the right unit. In addition, the pressure switches Pla and Plb are readjusted so that switch Pla opens at a lower pressure than switch Plb, and closes at a higher pressure than that switch. A restriction or choke should also be installed in the unloading valve Ba, while the control levers Lib. and L2b should` be moved to their local positions LO, and the control levers Lla and L2a should be moved to their remote positions RE.

With the apparatus arranged as described above on a drop in the pressure in the reservoirs Ra and Rb, switch Pla will close and close unloading valve Ba. Closure of contact lo of pressure switch Pia does not have any effect as. jumper 5| has been removed at this location and as control levers Lla and Llb are in their remote positions.

When the pressure in the reservoirs Ra and Rb drops further, pressure switch Plb closes and closes unloading valve Bb. Closing of contact l0 of switch Plb establishes a circuit to supply energy to the switch SIb and to heating element 3i) of device Qb as'the control levers Llb and L2b are in their local positions LO, while it also establishes a circuit to supply energy over the control wires 23 and 55 tothe switch Sla and to element 33 of device Qa. As a result, the compressors Cb and Ca start at once, While the compressors C2b and 02a start after a time interval. When the pressure builds up so that switch Plb opens, operation of the compressors is discontinued as explained above.

It will be seen, therefore, that the modication shown in Fig. 2 is arranged so that either unit4 may serve as either the controlling unit or as a controlled or subsidiary unit. Furthermore, little changein the adjustment of the equipment is required, while no change is required in the equipment itself to change a unit from a controllingto a subsidiary unit. This enables all of the units to be constructed alike and then employedwherever desired.

Although we have herein shown and described only two forms of compressor control systems embodying our invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of our invention.

Having thus described our invention, what We claim is:

1. In combination, a reservoir, a first and a second compressor for supplying uid to said reservoir, a first motor for driving the first compressor and a second motor for driving the second compressor, a rst magnetic switch effective when energized to establish av circuit to supply energy to the rst motor. a second magnetic switch effective when energized to establish a circuit to supply energy to the second 'motor` a time delay device eifective when supplied with energy to establish after a.Y predeterminedv time interval a circuit over which energy may be supplied to the second magnetic switch, a pressure switch responsive to the pressure of the iiuid in said reservoir, said switch being effective on a predetermined decrease in said Vpressure to s up ply energy to the winding ofv said first magneticV switch, to said time delaydev-ice and to establish the circuit controlled by said time delay device for supplying energy to the winding of said second magnetic switch. acontrol member governing the circuit of the winding of said first magnetic switch, said control member having a first position in which it permits the circuit governed by the pressure switch for supplying energy to the first magnetic switch to be established, a second` position in which it interrupts the circuit of said winding, a third position in which it establishes a circuit independentrofsad pressure switch for supplying energy to said winding, a second control member governing the circuit of' the winding of the second magnetic switch, said second control member having a first position in which it permits the circuits governed by the time delay device, the second magnetic switch and the pressure switch forsupplying energy to said winding to be established, a second position in which it interrupts the circuit of said winding, and a third position in which it establishes a circuit independent of said pressure switch and of said time delay device forsupplying energy to said winding.

2. In combination, a reservoir, a rst compressor for supplying fluid to a supply pipe from which fluid may be supplied through a first check valve to the reservoir, .a second compressor for supplying fluid through a second check valve to said supply pipe, a first motor for driving the rst compressor, a second motor for driving the second compressor, a rst magnetic switch effective when energized to establish a circuit to supply energy to the first motor, a second magnetic switch effective when energized to establish a circuit to supply energy to the second motor, a time delay device effective when supplied with energy to establish after a predetermined time interval a circuit over which energy may be supplied to the second magnetic switch, a pressure switch responsive to the pressure of the fluid in said reservoir, said switch having a contact which is closed on a predetermined decrease in the pressure in said reservoir and is elective when closed to establish a circuit to supply energy to the winding of the first magnetic switch, to said time delay device and to the circuit controlled by said time delay device for supplying energy to the winding of said second magnetic switch, said pressure switchcontact being opened on a predetermined increase in the pressure in said reservoir, and an unloadingvalve device controlling communication between saidsupply pipe and the atmosphere, said valve device being governed by the pressure switch so as to b e open when the switch contactisopen andto be closed when the switch contact is closed.

3. In combination, a reservoir, a first and a second compressor for supplying fluid to said reservoir, a first motor for driving the first compressor, a second motorfor driving the second compressor, a rst magnetic switch effective when energized to establish a circuit to supply energy to the rst motor, a second magnetic switch effective when energized to establish a circuit to supply energy to the Second motor, a time delay device effective when supplied with energy to establish after a predetermined time interval a circuit over which energy may be supplied to the second magnetic switch, a first pressure Switch responsive to the pressure of the fluid in said reservoir, said switch being effective on a reduction in the pressure in the reservoir to one predetermined pressure to establish a circuit to supply energy to the winding of said first magnetic switch, to said time delay device, and to the circuit controlled by said time delay device for supplying energy to the winding of said second magnetic switch, and a second pressure switch effective on a reduction in the pressure in said reservoir to a value less than said one predetermined pressure to establish a circuit independent of said rst pressure switch and of said time delay device for supplying energy to the winding of the second magnetic switch.

4. In combination, a reservoir, a first compressor for supplying fluid to a supply pipe from which uid may be supplied through a rst check valve to the reservoir, a second compressor for supplying fluid through a second check valve to said supply pipe, a rst motor for driving the first compressor, a second motor for driving the second compressor, a rst magnetic switch ef fective when energized to establish a circuit to supply energy to the first motor, a second magnetic switch effective when energized to establish a circuit to supply energy to the second motor, a time delay device effective when supplied with energy to establish after a predetermined time interval a circuit over which energy may be supplied to the second magnetic switch, a first pressure switch responsive' to the pressure `of the fluid in said reservoir, said switch having a contact which is closed on a decrease in the pressure in the reservoir to one predetermined pressure and is effective when closed to establish a circuit to supply energy to the winding of the first magnetic switch, to said time delay device, and to the circuit controlled by said time delay device for supplying energy to the winding of said second magnetic switch, said pressure switch contact being opened on a predetermined increase in the pressure in said reservoir, an unloading valve device controlling communication betweenl said supply pipe and the atmosphere, said valve device being governed by the pressure switch so as to be open when the switch contact is open and to be closed when the switch contact is closed, and a second pressure switch effective on a reduction in the pressure in the reservoir to a compressor units each having avrst anda secondl compressor supplying fluid to said reservoir, each unit having a first motor for driving the first compressor and a second-motor for driving thev second compressor, each unit having associated therewith a transformer from which energy may be supplied to the motors of such unit,` each unit having a rst magnetic switch effective when energized to establish a circuit to supply energy from the transformer for such unit to the rst motor of such unit, each unit having a second magnetic switch effective when energized to establish a circuit .to supply energy from the transformer for such unit to the second motor of such unit, each unit having a time delay device effective when supplied with energy to establish after a predetermined time interval a circuit over which energy may be supplied to the winding of the second switch of such unit, and a pressure switch responsive to the pressure of the fiuid in said reservoir, said switch being effective on a predetermined decrease in the pressure in said reservoir to supply energy to the winding of the first magnetic switch of each unit, to the time delay device of each unit, and to the circuits controlled by the time delay devices for supplying energy to the windings of the second magnetic switches of each unit- 6. In combination, a reservoir, a first and a second compressor unit each having a first compressor supplying fluid to a supply pipe from which fluid may ow through a check valve to the reservoir and a second compressor supplying fluid through a check valve to the supply pipe for suchV unit, each unit having a first motor for driving the first compressor and a second motor for driving the second compressor, each unit having associated therewith a transformer from which energy may be supplied to the motors of such unit, each unit having a rst magnetic switch effective when energized to establish a circuit to supply energy from the transformer for such unit to the first motor of such unit, each unit. having a second magnetic switch effective when energized to establish a circuit to supply energy from the transformer for suchunit to the second4 motor of such unit, each unit having a time delay device effective when supplied with energy to establish after a predetermined time interval a circuit over which energy may be supplied to the-winding of the second switch of such unit, each unit having a pressure switch responsive to the pressure of the fluid `in said reservoir, the pressure switch associated with the rst unit being effective on a decrease in the pressure in said reservoir to onepredetermined value to sup-- ply energy to the winding of the rst magnetic switch of each unit, to the time delay device of each unit, and to the circuits controlled by the time delay devices for supplying energy to the windings of the second magnetic switches of each unit, the pressure switch Iassociated with said first unit being effective on. an increase in the pressure in said reservoir to a second predetermined value to interrupt the supply of energy to the windings of the switches and to the time delay devices ofreach unit, each unit having an unloading valve governed by the pressure switch for such unit and controlling communication from the supply pipe of such unit to the atmosphere, the valve for the rst unit being open when the` switch interrupts the circuits controlled thereby and being closed when the switch establishes the circuits controlled thereby, the valve and pressure switch for the second unit being arranged and adjusted so that on a decrease in the pressure in the reservoir the valve for the second unit closes before the valve for the first unit closes and so that on an increase in the pressure in the reservoir the valve for the second unit opens before the valve for the first unit opens.

7. In combination, a reservoir, a firstv and a second compressor unit each having a first and a second compressor supplying fluid to said reservoir, each unit having a first motorl for driving the first compressor and a second motor for driving the second compressor, each unit having a transformer associated therewith,each unit having a rst. magnetic switch effective when energized to establish a circuit to supply energy from the associated transformer to the first motor and a seciondv magnetic switch effective when energized to establish a circuit to, supply energy from the transformer to the second motor, each unit having a first control lever governing the circuit of the winding of the. associated first magnetic switch and a second. control lever governing the circuit of the winding of the associated second magnetic switch, each lever having a local position in which it connects one terminal of the winding of the controlled switch to-a local contact, a remote position in which it connects the terminal of said winding to a remote contact, and an off position in which it interrupts the'circuit of the switch winding, each unit having a pressure switch responsive to the pressure of the fluid in saidreservoir, each pressure switch having a contact whichv is opened when the pressure in the reservoir increases toY a predetermined value and is closed` when the pressure in the reservoir decreases toapredetermined value, thel pressureswitch contactof each unitwhen closed establishing connection from one terminal of a source to the local. contact of that unit, each unit having a time delay device effective when supplied withk energy to establish after a predetermined time interval a circuit over which energy'may be supplied to the winding of the associated second switch and a control wire extending between the remote contacts of said units, eachA unit. being adapted to have. a removable connection installed between its local and remote contacts,l the first unit: having such a. contact installed, whereby when. the .control levers of the first unit. are in their local' positions and the control levers of the second unit are in their remote positions land the contact of the pressure. switch for said first. uniti's'closed energy "is supplied to the winding of the first switch of the firstv unit, to the time delay device of such unit. andto the circuit governed bysaid time delay device .for supplying energy tothe Winding of the second switch of, saidi first unit, and whereby energy is suppliedover said". control wires'- tov the winding of thel first switch of the second unit,

to the time delay device ofthe second unit and to the circuit governed by said time delay' device for supplying energy to the-winding of the second switch of saidl secondi unit.

` BERNARD E. OHAGAN.

ALLAN 'If'. JOHNSTON.

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
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US2459317 *Feb 7, 1944Jan 18, 1949Granberg Albert JFueling system
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Classifications
U.S. Classification417/5, 417/44.1, 417/12, 417/7, 417/18, 417/44.2, 417/6
International ClassificationH02P1/16, H02P1/54
Cooperative ClassificationH02P1/54
European ClassificationH02P1/54