Type DPSM-690 is used as a safety device on pressure lubricated refrigeration compressors, where under any operating conditions the lubricating oil pressure has to be kept higher than the suction pressure or crankcase pressure. The bellows marked OIL is connected to outlet side of compressor or at discharge from crankshaft lubrication system, and measures the lubricating oil pressure P1. Bellows marked LP is connected to the compressor crankcase and measures the crankcase pressure P2.