This example shows a test circuit built to check the pressure-flow characteristic of a direct-acting pressure-relief valve. The valve model consists of an orifice, a hydro-mechanical converter, a preloaded spring, and a hard stop.
An ideal flow rate source delivers fluid to a system through a variable orifice. As the orifice closes, pressure gradually builds up and eventually reaches the setting of the pressure-relief valve. At this pressure, the valve starts diverting flow to a tank and maintains preset pressure at the pump outlet. As the orifice is opened again, the pressure-relief valve is closed and the entire flow passes through the variable orifice.
The plots below show the behavior of the direct-acting pressure relief valve. As the load orifice closes, pressure in the system rises. When the system pressure reaches the pressure setting for the pressure relief valve, the valve opens which diverts flow away from the orifice and allows the system to maintain the set pressure of the pressure relief valve.