A pressure blowdown system for an oil-injected rotary screw air compressor having an output conduit mounted to a high pressure side of the compressor and having a feedback conduit mounted to an intake side of the compressor, includes a rigid container having a gas reservoir therein, the container having a rigid plate mounted thereon closing the reservoir, a rigid valve housing mounted to the plate, the housing defining a valve spool cavity and having a pressure blowdown vent, the cavity having first and second opposite ends, a valve spool slidably snugly mounted in the cavity for sliding translation between the first and second ends of the cavity, respectively into first and second positions in the cavity. Resilient means are mounted in the cavity for resiliently urging the valve spool from the first end towards the second end of the cavity. A first gas passageway in the plate provides unobstructed fluid communication between the first end of the cavity and the feedback conduit of the compressor. A second gas passageway in the plate provides unobstructed fluid communication between the second end of the cavity and the gas reservoir, where the gas reservoir is in unobstructed fluid communication with the output conduit of the compressor.