US 3271971 A
Description (OCR text may contain errors)
Sept. 13, 1966 JENSEN ETAL 3,271,971
LOW PRESSURE CUT-OUTS FOR REFRIGERANT COMPRESSORS Filed Dec. 31, 1964 fiz [3 LI L2 1 H W l4 EXPANSION CONDENSER Al VALVE EVAPORATOR COIL con.
RELAY SUCTION 2s TUBE HOLLQW STORAGE CHAMBER l8 1 CAPILLARY TUBE CAPILLARY 2' TUBE FIG.2.
l I l I I I 5', :5 TIME IN SECONDS |NVENTORS= ERIK H. JENSEN,
ALAN L. RHODES, BY %D.Qwh ATTORNEY United States Patent 3,271,971 LOW PRESSURE CUT-OUTS FOR REFRIGERANT COMPRESSORS Erik H. Jensen and Alan L. Rhodes, Staunton, Va., assignors to Westinghouse Electric Corporation, Pittsburgh,
Pa., a corporation of Pennsylvania Filed Dec. 31, 1964, Ser. No. 422,732 7 Claims. (Cl. 62-228) This invention relates to refrigeration systems having air cooled condensers; and relates more particularly to low pressure cut-outs for the refrigerant compressors of such systems.
When the refrigerant compressor of a refrigeration system having an air cooled condenser is shut down for several hours, with the outdoor ambient temperature at or below 60 F., pressure throughout the system equalizes at the saturation pressure corresponding to outdoor ambient temperature. When the compressor is again started, it will momentarily pull down the suction line pressure below that at which the usual low pressure cut-out operates, and shortly thereafter will raise the suction pressure above that at which the low pressure cut-out operates. As a result, the low pressure cut-out will cycle the compressor on and off if provided with an automatic re-set, or will require re-setting if provided with a manual re-set. This problem is well known, and there are available, electrical time delay devices for delaying the tripping action of low pressure cut-outs. Such devices are, however, complicated and expensive.
This invention is a simple, inexpensive, mechanical time delay device included in the connection of a low pressure cut-out to a suction line of a refrigeration system. In one embodiment of this invention, a fixed restrictor such as a capillary tube is connected to the interior of a suction line, and to the interior of a hollow storage chamber which is connected by another fixed restrictor such as a capillary tube, to a low pressure cut-out. During shutdown, the storage chamber fills with refrigerant at the pressure within the system. On start-up, the compressor momentarily pulls down suction pressure, but the time required to pull down the pressure within the storage chamber to that at which the low pressure cut-out op crates, is longer than required for the suction pressure to increase after having been momentarily lowered, so that the low pressure cut-out does not stop the compressor motor.
An object of this invention is to simplify and reduce the costs of low pressure cut-outs having built-in time delays.
This invention will now be described with reference to the annexed drawings, of which:
FIG. 1 is a diagrammatic view of a refrigeration system embodying this invention, and
FIG. 2 is a graph showing the operating characteristic of the system.
Referring first to FIG. 1, the discharge side of a refrigerant compressor C is connected by discharge tube 10 to a condenser coil 11 which is connected by a tube 12 containing an expansion valve 13 to an evaporator coil 14. The evaporator coil 14 is connected by a suction tube 15 to the suction side of the compressor C. The compressor C is driven by an electric motor CM which is connected by switch 16 of relay 17 to electric supply lines L1 and L2.
A fixed restrictor, shown as a capillary tube 18, is connected at one end to the interior of the suction tube 15, and is connected at its other end to the interior of hollow storage chamber 19. The interior of the chamber 19 is also connected by a fixed restrictor, shown as a capillary tube 21 to a pressure responsive means, shown as a bellows 22. The bellows 22 is mechanically connected to switch blade 23 of switch 24. The switch 24 is connected in series with a control switch 25 which may be a thermostat switch, and energizing Winding 26 of the relay 17, to the supply lines L1 and L2. The bellows 22 and its switch 24 form a low pressure cut-out.
The evaporator coil 14 is an indoor coil. The condenser coil 11 is an outdoor coil, or is cooled by outdoor air.
The graph of FIG. 2 has a vertical ordinate calibrated in pounds per square inch (p.s.i.) of suction line pressure, and has a horizontal ordinate calibrated in seconds of time after the start-up of the motor CM of FIG. 1.
In the operation of the system of FIG. 1, it is assumed that the system has been turned off for several hours by the opening of the switch 25, and that the outdoor temperature to which the condenser coil 11 is exposed is such that the pressure within the suction tube 15 and the storage chamber 20 is 60 p.s.i. The switch 24 of the low pressure cut-out is set to open when the suction pressure is reduced to 30 p.s.i., and is closed. When the control switch 25 is closed to restart the compressor motor CM, the relay winding 26 is energized through the closed switch 24, and closes its switch 16, starting the compressor motor CM. As shown by FIG. 2, the compressor C in about ten seconds after it is restarted, pulls the suction line pressure down from 60 p.s.i. to about 15 p.s.i. The usual low pressure cut-out switch with no time delay, would open when the suction pressure falls below 30 p.s.i., below the horizontal dashed line of FIG. 2. But the time required for the pressure at the bellows 22 to be reduced to 30 p.s.i. is, due to the storage capacity of the storage chamber 19, and the constriction of the capillary tubes 18 and 21, for example, about thirty seconds, and as shown by FIG. 2, before the end of that period, the suction pressure will have increased to above 30 p.s.i., so that the switch 24 does not open. The upper dashed line of FIG. 2 shows, in effect, how this invention pervents the pressure at the bellows 22 from dropping sharply shortly after start-up.
If there is a fault in the system which would cause a persistant, abnormally low suction pressure, at the end of the thirty seconds time delay, the pressure within the storage chamber 19 and at the bellows 22 would fall below 30 p.s.i., and the bellows 22 would open the switch 24, stopping the compressor motor CM.
What is claimed is:
1. A low pressure cut-out for a refrigerant compressor having a suction tube connected to its suction side, comprising a hollow storage chamber, means for connecting the interior of said tube to the interior of said chamber, pressure responsive means, means connecting the interior of said chamber to said pressure responsive means, and an electric switch operated by said pressure responsive means when the pressure within said chamber decreases to a predetermined pressure.
2. A low pressure cut-out as claimed in claim 1 in which said means connecting said interiors of said chamber and said tube is constricted means which adds substantial resistance to the flow of gas from said chamber into said tube when the pressure within said tube is lower than the pressure within said chamber.
3. A low pressure cut-out as claimed in claim 2 in which said means connecting said interior of said chamber to said pressure responsive means is constricted means which adds substantial resistance to the flow of gas from said pressure responsive means into said chamber when the pressure within said chamber is lower than the pressure at said pressure responsive means.
4. A low pressure cut-out as claimed in claim 1 in which said means connecting the interior of said chamber to said pressure responsive means is constricted means which adds substantial resistance to the flow of gas from 7 3 said pressure responsive means into said chamber when the pressure Within said chamber is lower than the pressure at said pressure responsive means.
5. A low pressure cut-out as claimed in claim 4 in which said means connecting said interior of said chamber to said pressure responsive means comprises a capillary tube.
6. A low pressure cut-out as claimed in claim 5 in which said means connecting said interior of said tube to said interior of said chamber comprises a capillary tube.
7. A low pressure cut-out as claimed in claim 1 in which said means connecting said interior of said tube to said interior of said chamber comprises a capillary tube.
References Cited by the Examiner UNITED STATES PATENTS 2,195,220 3/1940 McGarth 62--228 X 2,943,458 7/ 1960 Cohen 62-228 X 3,110,160 11/1963 Miner 62228,X
MEYER PERLIN, Primary Examiner.