Rotary compressors

Claim 1

A rotary compressor of the oil sealed type having an air inlet, an air delivery passage, a delivery space and a compression space, including: a servo valve; an unloader valve including a piston and a spring and controlling the air inlet and actuated by said piston subject to a pressure controlled by said servo valve which in turn is acted on by compressor pressure opposing a second spring; a minimum pressure valve including a third spring controlling the air delivery passage and opened by compressor pressure against said third spring and a restoring pressure; and venting means arranged to vent the delivery and compression spaces of the compressor and connected to a changeover valve operatively coupled to the pressure in a compressed air supply line to assume an on-load position when the said supply line pressure does not exceed a predetermined value greater than the normal working pressure, and to assume a no-load position when the said supply line pressure exceeds the said predetermined value, in which position it permits the venting means to vent the delivery and compression spaces, the compressor further including pressure sensitive switch means operably connected to said changeover valve so that when compressed air is being accepted by a load the changeover valve is in the on-load position and the servo valve and unloader valve modulate the inlet to maintain the nominal compressor delivery pressure with the venting means inoperative and the minimum pressure valve opened whereas when compressed air is not accepted the change-over valve assumes the no-load position, the minimum pressure valve closes the delivery, the venting means operates to vent the delivery and compression spaces, and the unloader valve opens to increase the compressor pressure when the latter sinks below a predetermined low value.