This is a model of an unloading relief valve with lumped volumes. If the pressure difference between the upstream port plus the pilot pressure and downstream port is higher than pMin, the valve starts to open. When the pressure difference reaches pMax, the valve is fully open. The spool model has first-order dynamics with time constant t1. This valve could be used in accumulator charging circuits to limit maximum pressure and the pump could be unloaded when the desired accumulator pressure was reached.

Implementation

This valve basically consists of an orifice controlled by a spool.

Reference

Industrial Hydraulics Manual, 5th ed., Maumee, OH: Eaton Hydraulics Training Services, 2008 p. 284.

medium	Value: Oil() Type: Medium Description: Medium in the component
V	Value: 0.0001 Type: Volume (m³) Description: Volume of control valve
Gleak	Value: 9.999999999999999e-21 Type: PressureDependentLeakage (m³/(s⋅Pa)) Description: Leakage between ports
pMax	Value: 21000000.0 Type: Pressure (Pa) Description: Pressure when valve is fully open
pMin	Value: 20000000.0 Type: Pressure (Pa) Description: Pressure when valve starts to open
t1	Value: 0.01 Type: Time (s) Description: Time constant for first-order system
AMax	Value: 0.001 Type: Area (m²) Description: Maximum opening area
Cd	Value: 0.62 Type: Real Description: Coefficient of discharge for the opening
kp	Value: 1 Type: Real Description: Pilot ratio; a positive value helps port_a