This is a model of a compound relief valve with lumped volumes. This valve is also known as a pilot-operated relief valve. It attempts to limit the pressure difference between ports a and b. This valve can be used to maintain a safe pressure level in the part of the system connected to port a. The path between port a and b can be opened by connecting the ventilation port to a low pressure.

Implementation

The model is an assembly consisting of a pressure relief valve, a pressure compensating valve, and a restriction. When pressure on port a builds up, a small flow goes into the chamber through the small chamber orifice. When the chamber pressure reaches the cracking pressure (pMin) of the pilot valve, it starts to open. When the pilot valve opens, it keeps the chamber pressure around the pilot valve's cracking pressure.

As the pressure difference between port a and the chamber reaches the cracking pressure of the piston (pMin), it starts to open. When the pressure difference reaches the piston's pMax, it is completely open.

The pMin and pMax parameters of the piston are much smaller than that of the pilot valve. The flow through the chamber orifice and the pilot valve is much smaller than the flow through the piston.

When the chamber is ventilated via the vent port, it causes the piston to open since the high pressure on port a is now unchallenged by the chamber pressure.

Reference

Industrial Hydraulics Manual, 5th ed., Maumee, OH: Eaton Hydraulics Training Services, 2008 p. 281.

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
pMaxPiston	Value: pMaxPilot / 50 Type: Pressure (Pa) Description: Pressure when piston is fully open
pMinPiston	Value: 0.95 * pMaxPiston Type: Pressure (Pa) Description: Pressure when piston starts to open
t1Piston	Value: 0.01 Type: Time (s) Description: Time constant for first-order system of the piston
AMaxPiston	Value: 0.001 Type: Area (m²) Description: Maximum opening area of the piston
CdPiston	Value: 0.62 Type: Real Description: Coefficient of discharge for the opening of the piston
pMaxPilot	Value: 21000000.0 Type: Pressure (Pa) Description: Pressure when pilot valve is fully open
pMinPilot	Value: 20000000.0 Type: Pressure (Pa) Description: Pressure when pilot valve starts to open
t1Pilot	Value: 0.01 Type: Time (s) Description: Time constant for first-order system of the pilot valve
AMaxPilot	Value: AMaxPiston / 10000.0 Type: Area (m²) Description: Maximum opening area of the pilot valve
CdPilot	Value: 0.62 Type: Real Description: Coefficient of discharge for the opening of the pilot valve
AOrifice	Value: AMaxPiston / 10000.0 Type: Area (m²) Description: Opening area of the chamber orifice
CdOrifice	Value: 0.62 Type: Real Description: Coefficient of discharge for the opening of the chamber orifice