3-way pressure reducing valve, piloted

The valve maintains a constant output pressure despite fluctuating input pressure. If the pressure continues to rise, the hydraulic fluid is drained off at T. The valve is then working as a pressure relief valve.

The valve is initially fully open from port P to A until the outlet pressure at port A exceeds the opening pressure of the pilot stage. Port A and the pilot stage are connected by a throttle nozzle, whose diameter can be specified.

When opening pressure of the pilot stage is reached, a pilot flow occurs, causing a pressure imbalance (due to the throttle nozzle) across the main spool, which then moves throttling the inlet flow from port P to A. If the pressure continues to rise, the connection between port P and A is closed and the connection between A and T starts to open.

The pressure regulation range dp_P is the pressure increment above the opening pressure p0_P of the pilot stage, at which the pilot stage is fully open.

The pilot stage starts to open, if pA > p0_P. It is fully open, when pA > p0_P + dp_P.

The pressure regulation range p_reg_M is the pressure increment above the closing pressure of the main stage, at which the main stage is fully closed.

The transition pressure range p_tr_M is the pressure increment above the pressure of the fully closed reducing valve needed to reach the pressure at which the pressure relief valve starts to open.

If pM is the inlet pressure of the pilot stage (behind the throttle nozzle), the main stage starts to close, when pA > pM + p0_M. It is fully closed, when pA > pM + p0_M + p_reg_M. As long as the pilot stage is closed, it is pA = pM.

The main stage starts to open, when pA > pM + p0_M + p_reg_M + p_tr_M. It is fully open, when pA > pM + p0_M + 2*p_reg_M + p_tr_M.

The hydraulic resistances relate to the fully open stages. A leakage for each stage can be specified.