When servicing or commissioning any equipment it is necessary to record the system pressures by fitting pressure gauges. To make this possible, all commercial systems generally include at least three service valves: suction, discharge and liquid shut-off. These are used to allow refrigeration gauges to be attached to the system; and, if needed, they are used to isolate the compressor from the rest of the system.
Suction and discharge service valves may be located on the compressor body of both reciprocating open-type compressors and semi-hermetic motor compressors. But on some compressor designs the service valves may be an integral part of the compressor head assembly. Hermetic motor compressors and some semi-hermetic models do not feature a discharge service valve. But the high side pressure may be obtained from the service valve on the liquid receiver or via a Schraeder-type valve fitted into the discharge line or on the receiver itself.