Page 210 - Valve Selection Handbook

Pressure Relief Valves 197

spring characteristic. This method of improving the back pressure toler-
ance of a pressure relief valve is offered by a number of manufacturers.
Alternatively, choose a valve with the next larger size orifice but restrict
the valve lift to the required flowrate. While the higher back pressure tol-
erance is achieved by shortening the decaying end of the lifting force
curve, larger inlet and discharge piping of the valve also lower the inlet
pressure loss and built-up back pressure from flow through the valve.

Figure 5-33. Force/Lift Diagram Displaying the Operational Behavior of Conventional
Spring-Loaded Pressure Relief Valves that Pop Open Partially Only and Then Continue
to Modulate Open (Typical Only).