Patent ID: 7409833

Claim:
A dual-mode compressor apparatus for receiving and compressing a gas from a gas supplying enclosure and discharging compressed gas into a gas receiving enclosure, the apparatus comprising: (a) a first compressor having a piston reciprocating in a cylinder between limits, the first compressor having a first suction port connected to receive gas from the gas supplying enclosure and having a first discharge port; (b) a second compressor having a piston reciprocating in a cylinder between reciprocation limits, the second compressor having a second suction port and having a second discharge port connected to an inlet of the gas receiving enclosure; (c) a 3/2 way valve having an inlet connected to the first discharge port, a first outlet connected to an inlet of the gas receiving enclosure and a second outlet connected to the second suction port; (d) a one way valve connected between the gas supplying enclosure and the second suction port for permitting passage of the gas from the gas supplying enclosure into the second suction port except when pressure at the second suction port exceeds pressure at the gas supplying enclosure; (e) an unloading valve having an inlet connected in communication with an unloading port through the cylinder of the second compressor between the reciprocation limits and having an outlet connected to the second suction port, the unloading valve being adapted to be closed except when pressure at the second suction port exceeds the pressure at the first suction port, the unloading valve, when opened, reducing the volume displacement of the second compressor in order to equalize gas mass flow rate through the two compressors; and (f) a first refrigeration evaporator that is said gas supplying enclosure; a second evaporator, the evaporators operating at different temperatures, a cooling control valve for controlling the flow of refrigerant into each evaporator and a temperature control for controlling the control valves and directing refrigerant into the evaporators, the temperature control being connected to an actuator that actuates the 3/2 way valve for switching the 3/2 way valve between its two states wherein the unloading valve is linked to a differential pressure actuator having two chambers, one chamber being connected in fluid communication with the first suction port and the other chamber being connected in fluid communication with the second suction port, the differential actuator being biased to close the unloading valve except when pressure at the second suction port exceeds the pressure at the first suction port; and wherein the gas is a refrigerant, and the gas receiving enclosure is a refrigeration condenser.