Pressure Reducing Valves

Pressure reducing valves keep the outlet pressure constant, also in case of a changeable, but always higher inlet pressure.

In hydraulic clamping systems, it is often necessary to pressurise single clamping elements or groups of clamping elements with reduced pressure.
This version with overpressure function compensates not only a pressure drop, but also a pressure increase above the preset pressure. For this purpose, a separate line to the reservoir must be provided.

Possible causes for a pressure increase are:

• Temperature increase (approx. 10 bar per 1°C)
• Force increase acts on the clamping cylinder
• Damage of the valve seat by swarf

Below the set outlet pressure, the hydraulic oil flows unhindered from P to A. In case of a pressure increase, the set spring force is overcome and a check valve cuts off the flow hermetically sealed. Thus, a further pressure increase is avoided, also in case of increasing inlet pressure p. In case of a pressure drop, e.g. because of a leakage at a cylinder, the check valve will be opened by a strong spring against the existing inlet pressure p. Hydraulic oil can continue flowing until the set outlet pressure is obtained. 

If the outlet pressure increases, e.g. because of oil warming, a pressure relief valve opens. Thus, oil in the outlet pressure area can drain off by the reservoir line until the preset outlet pressure is more or less obtained and the pressure relief valve is closed. A return flow from A to P is only possible if the inlet pressure p drops below the set outlet pressure.