force of the spring, the ball is unseated and allows fluid to pass.
The exact pressure at which this takes place is called the cracking pressure. This pressure can be
adjusted to any desired pressure by means of the pressure adjustment screw. Fluid passing the valving
ball flows into return lines and back to the reservoir.
Figure 3-1. Pressure Relief Valve.
A pressure reducer provides more than one level of pressure in a system that has a single hydraulic
pump. The reducer (Figure 3-2) consists of a three-port housing, piston, poppet and spring, adjusting
spring, and adjusting screw. A poppet is a valving device with a flat face. The three ports of the
housing are input pressure port, reduced-pressure port, and return port.