US2345797A - Compressor system - Google Patents

Description

April 1944- c. A. coRsoN 4 COMPRES SOR SYSTEM Filed March 27, 1943 1 2w INVENTOR E dfiuaJCSJI-Cordon.

Hi5 ATTORNEY.

Patented Apr. 4, 1944 comaassoa srs'ram Charles A. Corson, Painted Post,-N. 1., anig nor to Ingersoll-Rand Company, NewYork, N. Y., a corporation or New Jersey Application March 27, 1943, Serial No. 480,783

8 Claims.

This invention relates to compressor systems and, more particularly, to a system of regulation for air or gas compressors.

It has been customary to operate air or gas compressors by driving them by electric or other motor controlled by an automatic pressure operated switch, so that when some predetermined maximum discharge pressure is reached the motor will automatically shut down to be restarted automatically when the pressure drops to a predetermined minimum speed. This system has an advantage over other systems in which the compressor 1s unloaded while the motor and compressor continue to idle, in that no electric current is used during the stopped period. This advantage disappears, however, if the stopping and starting occur very frequently for the reason that during the starting period the motor draws excessive current. It is thus seen that there is a point at which it would be advantageous to merely unload the compressor without stopping it. This latter method of operation is known as "constant-speed operation, while the other is usually called the stop-start system. The stop-start" method is generally found desirable when the demand for air is relatively low and the constant-speed" system i more advantageous during periods of greater demand and when the compressor loads and unloads frequently.

It is an object of this invention to provide a compressor system which is adapted to operate on both the constant speed and the start-stop system, and in which the system to be used is automatically selected.

It is a further object of the invention to provide a system of this character in which a minimum stopping period for the motor is pre-established so that the most economical of these types of operation may result.

Other objects and advantages of the invention will become in part obvious and in part pointed out hereinafter.

In the drawing in which similar reference characters refer to similar parts and in which is shown a preferred embodiment of the invention,

Figure 1 is an end elevation of a compressor and its regulating apparatus, certain portions of the regulator being shown in vertical section and other parts being broken away to show more clearly the internal construction and the operation of the various parts, the electric wiring and piping being shown schematically;

Figure 2 is a top plan view taken along the line 2-4, looking in the direction of the arrows in Figure 1 and showing portions of the switch and the controller: and

Figure 3 is a section taken along the line 3-4 of Figure 1 looking in the direction of the arrows and showing the internal construction of the switch mechanism of the controller.

Referring to the drawing, a compressor of a standard construction is shown at A having low pressure cylinders B and a high pressure cylinder C. In this instance, the compressor'A is shown driven by a suitable electric motor D and the driving connection consists of a pulley E on the electric motor D and a pulley F on the compressor A and a driving belt G.

The compressor A is provided withan intake manifold H leading to the low pressure cylinders B. From these cylinders the air is. discharged into an intercooler J through suitable piping K and thence by piping connection L to the high pressure cylinder C. High pressure air is conducted therefrom to a receiver M throuzh a discharge pipev N.

At the intake manifold H is provided a suitable unloading device whichconsists of a casing 0 flanged as at P for attachment to the manifold and provided internally with a balanced valve Q controlling communication between an outer chamber R connected with atmosphere, and an inner chamber S leading to the manifold H.

Valve Q is biased to its open position shown in the drawing by a spring T. The valve is closed by pressure of a fluid actuated piston U bearing against a projection V on the valve. A suitable cylinder W is provided for the piston U into which pressure fluid is adapted to be admitted from a chamber Y suitably connected, as will be described hereinafter, to the source of pressure fluid M.

A suitable source of current is provided from the electric mains i and 2 having a main switch 3,1or connection with the motor leads 4 anad 5. Interposed between the switch 3 and lead 4 is a magnetic starting switch comprising the armature 6 and the stationary contact I. As is customary, the armature 6 is biased to its open position by a spring 8. Tension of the spring I is overcome upon closing of the switch 3 by a solenoid 9 included in a circuit bridged across the leads 4 and 5, preferably between the switch 3 and the contact 1 in respect of the lead 4, the bridged circuit include the conductors i0 and II leading to contacts I! and ll of a pressure switch l4 adapted to control stopping and starting of motor D. Cooperating with the contacts l2 and i3 there is provided a circuit closing member l5 operated by the switch. The pressure operated switch I4 is of conventional design and is operated by a plunger l6 cooperating with a plate |1 against which a diaphragm I8 is adapted to exert pressure. The diaphragm i3 is housed within a casing l9 consisting of a flanged upper half 23 and a corresponding flanged lower half 2|, between which the diaphragm is clamped. Pressure fluid is admitted to the space pressure switch I 4 is of the snap" variety and there is some set difierence between the pressures at which the plunger I6 is actuated upwardly and downwardly. For instance the plunger l6 may be adapted to operate at a receiver pressure .of 100 pounds and to be restored at a predetermined low pressure of 83 pounds. It is understood, of course, that the upward motion of the plunger l6 operates to open the circuit at switch points I2 and I3 tending to-de-energize the solenoid 9 thereby breaking contact between the armature 6 and stationary contact 1. Normally, this will tend to stop the motor D by opening its circuit. Upon dropping of the plunger I6 at the predetermined low line pressure, the contact member I5 is adapted to restore the circuit at the switch contacts l2 and I3 to re-energize the solenoid 9 and to close the motor circuit.

The pressure switch I4 is also designed to operate a three way pilot valve 24'which consists of a body portion 25 provided with upper and lower valve seats 26 and 21 respectively,

connected by bore 28. Within the bore 28 is disposed a valve stem 29 provided at its ends with upper and lower valve heads 33 and 3| respectively. The stem 29 is o! sufllcient length so that only one oi. the valve heads 33 and 3| can be seated on the seatings 26 and 21 respectively, at any one time. The stem 29 is arranged to be shifted so that these valves seat on their respective seatings by means of a lever 32 pivoted as at 33 on a bracket 34 formed integrally with the body 25. The lever 32 is adapted to press against an extension 35 of the stem 29 so that as the lever 32 moves upwardly, valve 3| seats and the valve 33 is unseated, and as the lever drops the valve 33 seats and the valve 3| is unseated.

The upper part of the body 25 is provided with a chamber 36 closed by a plug 31 and communicating through a passage 38 and a suitable pipe 39 with the source of pressure fluid in the receiver M. The pipe 39 may, in this instance. connect with the conduit 23 for this purpose.

The bore 28 in the pilot valve 24 is in communication with a tapped hole 43 to which is attached a pipe or conduit 4| leading to the unloader at the chamber Y. It will thus be seen that the pilot valve 24 is adapted to alternatively connect the chamber Y and the unloader with the source of pressure fluid from the receiver M or with exhaust, depending upon the seating of the valves 33 and 3|.

To operate the lever 32 the pressure switch I4 is provided with a pin 42 extending to the exterior of the switch casing to engage the lever 32. The pin is actuated by the plunger i6 to move in the arcuate slot 43 so that when the pressure switch |4 operates to open the circuit 01 passageway 45 formed in the wall of the chamber Y, provided at one end with a seat 46 cooperating with a ball check valve 41 disposed in a counterbore 48 and pressed to its seat by a light biasing spring 49. Counterbore 43 communicates with the chamber Y by hole 53. The valve 41 is adapted to be unseated by fluid admitted from the conduit 4| under pressure, but is adapted to prevent escape of pressure fluid from the chamber Y. Exit from the chamber Y is provided by plug 5| having a very small oriflce 52 delaying emission of pressure fluid from the chamber.

Operation of the solenoid 9 is also controlled by a circuit bridged across the conductor II and the motor lead 4 and including the conductors 53 and 54respectively, and a switch 55 forming a part of a second controller 56. Switch 55 is shown in section in Figure 3 and includes a swinging contact I51 connecting with the conductor 53 and a stationary contact I58 to which the conductor 54 is attached. The swinging contact I51 is actuated by extremely small movement 01' a plunger I59 extending through the switch casing 63.

- The second controller 56 comprises a casing formed in two portions-an upper casing portion 51 and a lower casing portion 58, joining at two flat faces adapted to receive between them a flexible diaphragm 59 of any suitable material such as, for instance, rubber. Within the casing formed by the portions 51 and 58 are two chambers 63' and 6| divided by a partition 62 formed integrally with the upper half 51 and continued by the lower partition 63 and the lower half 58. The chambers are divided horizontally by the diaphragm 59. The lower part of the chamber 6| is relatively large as indicated at 64. The chamber 63 below the diaphragm 59 is provided with anaperture 65 which communicates by conduit 66 leading into the conduit 23 with the source of discharge pressure fluid in the receiver M. The diaphragm 59, therefore, is at all times within the lower part 01' chamber 63' exposed to the discharge pressure 01 the compressor A.

The pressure against the diaphragm 59 is opposed in chamber 63' by a spring 61 bearing against a washer 68 overlying the diaphragm 59 and held in place by a bolt 69. Tension on the spring 61 is adjustable by means of a screw 13 provided with a cap 1| fitting the upper end of the spring 61. The screw 13 is threaded in the upper wall of the upper casing half 51 at, the threaded aperture 12. Adjustment of the screw is maintained by a lock nut 13.

Chamber 64 is adapted to receive pressure fluid through an orifice 14 in the wall of the chamber and connected by a pipe 15 and a conduit 16 to the conduit 4|. Chamber 64 thus receives pressure fluid under the control of the pilot valve 24 and the controller l4. Likewise under the control of the pilot valve 24 pressure fluid is exvalve 19 controlling a passageway 99 leading toa chamber 9I. A reducing pipe plug 92 in chamber 9| is provided with a nipple 99 leading to the conduit I5. Pressure on diaphragm 59 within the chamber 54 is opposed by a coil spring 94 bearing against washer 95 bolted to the diaphragm 59 by means of the large headed bolt 99.

The compression of spring 94 is regulated by means of the threaded screw 91 passing through the threaded aperture 99 in the top wall of the casing half 51. In this instance the adjustment is set by means of shims 99 under the head of the screw 99.

At such times as the pressure under the diaphragm 59 is unable to withstand the pressure of the springs 51 and 94, the bolts 99 and 95 rest upon stops 99 and 9|, respectively, which are formed integrally with the lower casing half 59.

Motion of the diaphragm 59, due to the pressures thereunder, is adapted to be transmitted to the switch 55. For this purpose the screws I9 and 91 are hollow and provided with push rods 92 and 99, respectively, bearing against the stems of the bolts 59 and 95, respectively. At its upper end push rod 92 is provided with a nut 94 cooperating with a U shaped lever member 95 at an aperture 95. Likewise, push rod 99 is provided with a nut 91 cooperating with the lever 95 at an aperture'99.

Push rod 92 bears against the top of the stem of bolt 59 and is held in contact therewith by a light leaf spring 99. Likewise, the push rod 93 is held in contact with the corresponding bolt 85 by means of a light spring I99.

The U shaped lever 95 is Journaled at the ends of its arms on a bearing rod I9I mounted in a bracket I92 at the top of the upper casing half 51 upon which bracket also are mounted the leaif springs 99 and I99. Motion of the U shaped lever 95 is adapted to transmit motion of the diaphragm 59 to the plunger I59 on the switch 55. To this end the lever is provided with a recess I93 to receive the plunger.

The weight of the lever 95 is counterbalanced by a light coil spring I94 seated on the top of the switch 55 and contained in a pocket I95 of the U shaped lever 95.

As can be readily understood from the above description, the actuating force for the switch 55 is the pressure of the springs 99 bearing downwardly. When this pressure is overcome by upward motion of the push rods 92 and 93, the switch is released by the spring I94. The switch 55 is extremely sensitive and the contacts I51 and I59 are closed by an extremely slight motion of the plunger I59 of the order of one or two thousandths of an inch.

Under certain conditions, as will be described hereinafter, it is desirable that the switch or controller I4 be operated at a close range of pressures in the receiver M instead of at the wider range as above referred to. To this end, a range changing device I95 is provided, whose purpose is to change the operational pressure range of the plunger I5. This is accomplished by reducing the effect of the high pressure on the diaphragm I9. The range changing device I95 consists of a cylinder I91 provided with an upper head I99 and a lower head I99 and a piston II9' fitting the bore of the cylinder. The upper head I99 is provided with a passage II9 communicating by means of a pipe III with the manifold H. The lower head I99 is provided with a valve seat 2 in bore III, which communicates with the space in the casing I9 under the diaphragm I9 by means of a pipe 4. A restrictive orifice III is provided in the bore III for the purpose of controlling the flow of pressure fluid throughthe pipe H4. The bore of the cylinder III is provided with a vent I I9 to atmosphere by means of which pressure fluid entering the bore may escape to the open air when the valve seat H2 is opened at a valve III formed integrally with the piston I I9. Normally, the piston I I9 is biased by means of a spring I I9 to its closed position. I

The apparatus above described has been adapted to permit the compressor A to operate at constant-speed" during the periods of normal demand, that is to say, without shutting down. Additionally, it enables the compressor to convert automatically to operation at start-stop" during periods of low demand such as would be found perhaps at night.

Under all circumstances it will be noted that when the .pressure in the receiver M rises to some predetermined value, as for instance 100 pounds,

the diaphragm is forced upwardly to cause the controller I4 to open the circuit including contacts I2 and I9. Simultaneously, the pilot valve 24 is operated to open communication between the supply conduit 29 and conduit 4I thereby admitting motive fluid through the passageway 45 past the check valve 41 and through aperture 59 into the chamber Y, whereupon the piston U is forced against the pressure of the spring T to move the intake valve Q to closed position. Admission to the inlet manifold H is thereby cut of! from atmosphere and the compressor A is thereby unloaded. The motor D, however, does not immediately stop because its circuit is not opened by operation of the controller I4. The switch points 5 and I are held closed by the solenoid 9 since its circuit is still closed at the switch 55.

As has been indicated above, operation of the pilot valve 24 by the controller I4 also controls the second controller 55 in the following manner: Motive fluid from the receiver M is constantly in communication with the chamber 59' under the diaphragm 59, which at a predetermined high pressure would tend to overcome pressure of spring 51 and to lift the push rod 92 upwardly to release the U shaped lever. This lever is, however, normally prevented from moving upward by pressure of holding the lever down through the medium of the push rod 99 and the nut 91. Therefore, if the U shaped lever 95 is to release the switch 55 at all, pressure holding the push rod 92 in raised position must be maintained until the push rod 93 is raised. The mechanism operating the push rod 93 is, therefore, a timing mechanism which, in conjunction with the operation of the push rod 92, determines whether the switch 55 is to open or not. To this end, the chamber 54 is adapted to be filled slowly at some predetermined rate. with pressure fluid from the receiver M. This is accomplished through the medium of the pilot valve 24 which, while admitting motive fluid to operate the unloader, also admits through the conduit I5 and pipe 15 motive fluid to the chamber 54. The size of the orifice I4 through which the motive fluid passes is suitably selected so that in some given time the chamber '54 will build up pressure to a suitable value to raise the diaphragm 59 thereby lifting the push rod 99 to release the U shaped lever 95.

Assume that the operating range of th controller I4 is setat 20 pounds, that is to say, to operate the pilot valve 24 at 100 pounds per square inch and to restore it at 80 poundsreceiver pressure, the second unloader may be set so that the push rodjl, .upon a drop in pressure from 100 pounds to 98 pounds, will re-engage the lever 95 so as to prevent-its operation. Simultaneously, by suitable selection of the size of the nozzle 14 and tensioning of the spring 84, the pressure may be regulated to build up within 30 seconds in the chamber 64 so as to start raising the push rod 93. Thus it will be seen that if the switch 55 is to be open under these conditions. the receiver pressure will have to drop somewhat less than 2 pounds in 30 seconds, in which case both push rods 92 and 93 will. be in raised position simultaneously to release lever 95,-. In that case the circuit of the holding c911 [will be open both at the switch 55 and at the contacts I2 and I3 which causes the switch to open at contacts 8 and I to stop motor D.

Conditions just described may be considered those of low demand and they determine, by means of the controller 56, a minimum stopping period for the motor D. Under these specific conditions, that is, with the pressure dropping at the rate of something less than 2. pounds in 30 seconds, it will be seen that the minimum stopped period for the, motor D will be 5 minutes for a pressure range of 20 pounds, the assumed settlng oi the controller l4.

It will be noted that while the relativ motions of the push rods 82 and 93 may client the operation of the switch 55 to open the circuit of the holding coil 9, they cannot under any condition operate to close the circuit of that coil, in-. asmuch as the circuit including the switch '55,

also includes the switch contacts 6 and 1. There-.

fore, the switch 55 can never start up the motor D once it has stopped. In other words, when the controller 56 has operated to shut down the motor D, restarting of the motor can only-"be effected by the controller H which, as one of its down before the pressure in the chamber '64 has had time to build up to release the lever. The switch 55, therefore, stays closed. It may be said, therefore, that the controller 56 is operated by the'rate of drop in pressure per unit of time to openand close the circuit of motor D.

. Under such conditionathe controller H has the-effect of operating only the intake unloader, which is effected entirely through the pilot valve 24. Thus, during periods of great demand, the motor D operates-continuously while the intake unloaderperformsthe function of loading and unloading the compressor A. i It will be seen that the motor D is stopped by operation of controller 56 at some definite period after operation of the controller 14. Correspondingly, the compressor is also first unloaded by the intake unloader. It is considered desirable, as it well known in the art, that the unloader should keep the compressor unloaded while the motor D is starting, since it is uneconomical to start any motor under load. Accordingly, upon operation of the controller l4 to restart the motor D, the pilot valve 24 operates to release the motive fluid from the chamber Y. Under these conditions, the check valve 4! is held closed by the spring .49 and the exhaust of motive fluid is permitted only through the small orifice 52 of a size which would allow the lapse of several seconds before the pressure in the chamber Y will drop sufficiently to permit the compression of the spring T to' throw the valve Q to its open position.

While the chamber 64 is arranged to be. filled with pressure fluid very slowly by way of the orifice 14, it is preferablyexhausted rapidly by way of the check valve 19 when the pilot valve 24 is restored to its normal position exhausting the air-in the line .4l.

During the periods of great demand for pressure fluid it is often convenient to operate the compressor A at a closer pressure range than when running start-stop and this is the purpose of the range-changing device I06. While the compressor A is running unloaded, the pressure in the manifold H is subatmospherlc. This suction is transmitted to the bore of the cylinder I01, lifting the piston III! to uncover the valve seat H2 and permitting air to escape through the pipe H4 slowly through the orifice H5 to atmosphere by way of the port 6. The escape of air in this manner has the effect of reducing, to a certain extent, the pressure under diaphragm l8 since admission to the space under the diaphragm is also restricted by the orifice 22. Thus, while the plunger i6 may have been forced upwardly by a pressure of 100 pounds per square inch to actuate the controller l4, subsequent action of the intake unloader and the rangechanger I08 may immediately drop the pressure under the diaphragm ii to a value, for instance of 90 pounds. Then,- upon reduction of the pressure in the receiver M to 90 pounds, there will be a corresponding reduction in the pressure under the diaphragm to, let us say, 80 pounds, which will cause the controller I4 to operate, thereby reloading the compressor A. In this manner, the

pressure operating range may be changed from, for instance 20 pounds to 10 pounds.

As will be obvious, the range-changing device I06 is not in effect when the motor D is operating on the stop-start" conditions for, in such cases, the intake manifold H does not remain under vacuum for any great length of time while the motor D is stopped.

The change of range above referred to is desirable inasmuch as during large demand periods it is desirable to keep the pressure in the receiver M fairly constant, while under stop-start conditions constant pressure is not so desirable as it causes more frequent starting and stopping of the motor D.

I claim:

1. A compressor system including a compressor. a driving motor therefor, acontroller operated by the compressor discharge pressure adapted to stop the motor at a predetermined high pressure and to restart the motor at a predetermined low pressure, a compressor unloader operated by pressure fluid controlled by said controller to unload thecompressor at said predetermined high pressure and to reload the compressor at the predetermined low pressure, and a second controller to delay .the stopp ng of the motor after operation of the first controller and to pre-establish the minimum stopping period of the motor.

2. A compressor system including a compressor, a driving motor therefor, a controller operated by the compressor discharge pressure adapted to stop the motor at a predetermined high pressure and to restart the motor at a predetermined low pressure, a compressor unloader operated by pressure fluid controlled by said controller to unload the compressor at said predetermined high pressure and to reload the compressor at said predetermined low pressure, means to delay operation of said unloader to reload the compressor for a givenperiod after said predetermined low pressure is reached, and a second controller adapted to delay stopp or said motor at said predetermined high pressure, said controller including means for pre-establishing the minimum stopping period of said motor controlled by the rate of drop in the compressor discharge pressure when the compressor is unloaded by said unloader.

3. A compressor system, including a compressor, a device for unloading the compressor, a motor for driving the compressor, a pressure fluid operated controller for stopping and restarting the compressor motor and having a predetermined pressure range, a second pressure fluid operated controller for the motor having a shorter pressure range than the first said controller and provided with a timing mechanism controlled by the flrst controller to pre-establish the minimum stopping period 01' the motor.

4. A compressor system, including a compressor, an electric driving motor therefor, a magnetic switch mechanism for controlling said motor, a controller operated by the compressor discharge pressure for said switch mechanism for stopping and restarting the motor, and means associated with said switching means for preestablishing the minimum stopping period of the motor, said means being controlled by the rate of drop in the compressor discharge pressure.

5. A compressor system, including a compressor, an electric driving motor therefor, a magnetic switch mechanism for controlling said motor, a controller operated by the compressor discharge pressure for said switch mechanism for stopping and restarting the motor, a compressor unloader operated by the controller, and means associated with the switch mechanism for pre-establishing'the minimum stopping period of the motor, said means being controlled by the rate of drop in the compressor discharge pressure when the compressor is unloaded.

8. A compressor system, including a compressor, an electric driving motor therefor, a controller for said switch mechanism operated by the compressor discharge pressure to stop the motor at a predetermined high pressure and to restart the motor at a predetermined low pressure, a compressor unloader operated by pressure fluid and controlled by said controller to unload the compressor at said predetermined high pressure and to reload the compressor at the predetermined low pressure and a second controller associated with said switch mechanism to delay stopping of the motor after operation of the first said controller and to pre-establish the minimum stopping period of the motor.

'7. A compressor system including a com pressor, an electric driving motor therefor, a switch mechanism for controlling the operation of said driving motor, a controller for said switch mechanism operated by the compressor discharge pressure to stop the motor at a'predetermlned high pressure and to restart the motor at a predetermined low pressure,'a compressor unloader operated by pressure fluid controlled by said controller to unload the compressor at said predetermined high pressure and to reload the compressor at said' predetermined low pressure, means to delay reloading operation of said unloader for a given period after said predetermined low pressure is reached, and a second controller associated with said switch mechanism adapted to delay stopping of said motor at said predetermined high pressure, said controller including means for pre-establishing the minimum stopping period of said motor and controlled by the rate of drop in the compressor discharge pressure when the compressor is unloaded by said unloader.

8. A compressor system, including a compressor, an electric driving motor therefor, a switch to control the circuit of said motor, a holding coil for said switch, a controller for said holding coil operated by the compressor discharge pressure to stop the motor at a predetermined high pressure and'to restart the motor at a predetermined low pressure, a compressor unloader operated by pressure fluid controlled by said controller to unload the compressor at said predetermined high pressure and to reload the compressor at said predetermined low pressure, and a second controller associated with said holding coil adapted to delay stopping of said motor at said predetermined high pressure, said second controller including means for pre-establishing the minimum stopping period of said motor and controlled by the rate of drop in the compressor discharge pressure.

CHARLES A. CORSON.

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