B - Control Principles - Chicago Pneumatic QRS 20 Instruction Manual

B - Control principles

1 - On/Off Control (see Fig. 5)
Models, all versions
The QRS 20-25-30 units are fitted with an automatic control system,
enabling the machine to be stopped after it has run unloaded for a
given (adjustable) period of time. This unloaded period is necessary
to avoid excessively close start-ups in periods of unstable compressed
air consumption.
When the compressor reaches the maximum pressure (measured
by the pressure sensor - item. 36), the solenoid valve (item. 35)
releases to the atmosphere the compressed air. The internal pres-
sure closes on one hand the suction box and on the other hand the
blow off piston. This results in the release of the internal pressure
of the receiver via the by pass check valve."
The compressor draws in air via a by-pass valve (item. 25).
The low pressure obtained in the oil tank enables the compressor
to be lubricated and cooled during the whole unloaded period.
If the compressed air pressure in the user network reaches the
minimum cutting-in value before the end of the no load
operation time out the solenoid valve (item. 35) is actuated
causing the suction valve to open and the vent to close. The
compressor then operates at full output rate.
When the compressor stops, the solenoid valve (item. 35) is no
longer powered and closes; the suction housing closes and the
oil tank is evacuated. The receiver is thus brought back to
atmospheric pressure for the next start-up.
23
25
Chicago Pneumatic Compressors
62 305 454 65
Fig. 5 - On/Off Control
38
21
27
60
20
20. Compressor
21. Suction housing
23. Air filter
25. By-pass check valve
26. Oil filter cartridge
27. Safety valve
34. Built in minimum pressure valve / Filter support
35. Solenoid valve
36. Pressure sensor
38. Pneumatic vacuum piston
41. Ventilation
47. Thermostatic valve (built in filter support)
49 Oil separator
51 A Air cooler
51 H Oil cooler
57. Oil receiver
60. Temperature sensor
63. Manometer
35
63
49
26
37
57
26
Key Fig. 5
41
34
51A
51H
47
36
01/2008
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