calibrated spring that allows oil to bleed off at a given pressure. If the engine's manufacturer decides that 50 psi (344.75 kPa) of oil pressure is desirable in the engine, the pressure-regulating valve (Figure 12–17) will not allow the pressure to go beyond 50 psi (344.75 kPa). When the pressure on the output side of the pump reaches this point, it presses against either a check valve, a ball, or a plunger, forcing it to unseat and allow oil to bypass and return to the inlet side of the pump.