Gems PDTF Series is a factory set temperature switch for the protection of all types of, internal combustion engines, pumps, compressors, gear boxes, hydraulic reservoirs,, marine and industrial power plants. Model PDTF will withstand acceleration to 8G., Its compact and rugged construction allow it to be mounted in the toughest OEM, applications. The PDTF utilizes a liquid-fi lled capillary to sense temperature changes., The liquid expands as the temperature increases, causing the capillary pressure to, increase.