The tubing connected to the bellows is usually copper capillary tubes, high-pressure rubber hose, or a type of high-pressure plastic with a braided aluminum shrouding. Fig. 2 illustrates the internal action of the bellows-type controller.
Transducer-type controllers use a pressure transducer that senses a combination of oil pump discharge pressure and crankcase pressure. The pressure transducer has two separate ports to sense both crankcase pressure and oil pump discharge pressure. The subtraction or difference between these two pressures (NOP) is accomplished by the transducer mechanically. The pressure transducer is connected to an electronic controller by wires. It then transforms a pressure signal to an electrical signal for the electronic controller to process.