A reciprocating compressor resembles a car engine: the crankshaft moves the pistons back and forth in the cylinders, refrigerant entering through the suction valve is compressed and leaves through the discharge valve. There are models with one to eight cylinders; the number of cylinders and the speed determine capacity. It is produced as hermetic (small), semi-hermetic (medium to large) and open type (ammonia).
Its greatest strength is flexibility: it works at every evaporating temperature from −45 °C to +15 °C and with almost every refrigerant; stepped capacity control is done by cylinder unloading; with economiser and two-stage versions it suits low-temperature applications such as blast freezing and deep freezing. Semi-hermetic reciprocating compressors can be repaired on site.
Its weak points compared with scroll are higher vibration and noise, more moving parts and sensitivity to liquid reaching the suction (liquid cannot be compressed; the valves break). With correct superheat, a crankcase heater and oil return it runs for decades. Our low-temperature condensing units use Bitzer and Frascold semi-hermetic reciprocating compressors.