Direct Operated Hydraulic Pressure Relief Valve

Function

The function of the direct acting relief valve is to relieve system pressure at a set point, thus limiting the pressure in a hydraulic system. The hydraulic pressure limitation is there for several reasons:

Protection of components
Safety, an unlimited system can lead to very dangerous situations (see dangers of fluid injection)
Power limitation, the drive component of any system will have limitations, a relief valve will serve to limit the power used.

How does a direct acting hydraulic pressure relief valve work?

The image to the right shows an artist’s impression of a relief valve, the fluid enters the chamber on the left shown by the arrow and "P". direct-relief-valve_pictoral

The blue poppet or sometimes a cone or a ball bearing covers the entrance and is held in place by a spring. The spring force can be varied by compressing via a mechanical screw. As the hydraulic fluid pressure in the "P" line increases it will eventually overcome the force keeping the poppet in place, thus allowing the fluid to travel back to the reservoir more commonly known as tank. This balance of forces will remain until the hydraulic pressure in the system decays.

This is known as a direct operated pressure relief valve due to that the full flow of the system acts on the poppet and passes through the chamber