Oil safety controllers often come in two types: bellows (mechanical) and transducer (electronic).
Bellows-type controllers sense both crankcase pressure and oil pump discharge pressure, usually through some type of tubing, and then transmit the pressure to flexible bellows (Figure 1). The tubing connected to the bellows usually consists of copper capillary tubes or a type of high-pressure plastic with a braided aluminum shrouding. Figure 2 illustrates the internal action of the bellows-type controller.