Patent ID: 8002527

Claim:
A screw-type compressor, comprising: a motor driven and dry operating compressor unit that has a suction side and a pressure side; a butterfly valve disposed in an intake line connected to said suction side of said compressor unit; an adjustment cylinder that is adapted to mechanically shift said butterfly valve; a pressure line connected to said pressure side of said compressor unit, wherein said pressure line, via the interposition of a check valve, is adapted to be connected to a compressed air system for a supply of compressed air thereto; and a pneumatically controlled air relief valve, wherein said pressure line is connected to said air relief valve via an air relief line for a relief of pressure during idling of said compressor unit, and wherein at least during idling of said compressor unit said air relief valve is adapted to be acted upon by the pressure that is effective on said pressure side of said compressor unit, wherein a valve piston is movably disposed in said air relief valve, wherein control air connections are provided in said air relief valve on opposite sides of said valve piston, wherein a first switching valve that controls said valve piston is connected to said control air connections, and wherein a control air line connects said first switching valve to said pressure side of said compressor unit, and wherein the control air line are always connected with the pressure side of the compressor unit, so that said valve piston is moved by the pressure existing on the pressure side of the compressor unit, wherein a bypass is disposed between said pressure line and the compressed air system, wherein said bypass bypasses said check valve, wherein a pressure valve that has two positions is disposed in said bypass, and wherein said control air line is connected via said pressure valve either with said pressure line or with the compressed air system, so that depending on an inherently present pressure in the pressure line upstream of the check valve or in a pressure system downstream of the check valve, the respectively higher pressure is utilized for actuation of the air relief valve, and wherein the butterfly valve and the air relief valve are configured to be controlled independently of one another via respective drives for adjustment of a consumption-dependent position of the butterfly valve and for proportional regulation of a quantity delivered by the compressor.