Why does the positive displacement pump I purchased come with a pressure relief valve?
Positive displacement pumps deliver a constant volume with every revolution of the shaft, which is relatively independent of pressure. This results in a pump performance curve that has a relatively constant flow rate as pressure increases or decreases (see May 2015 Pump FAQ for more on the performance curve for a positive displacement pump).
The constant flow characteristic can result in system overpressure when the discharge flow is blocked or restricted. For this reason, positive displacement pumps should have protections in place to ensure over-pressurization does not occur.
Image 2 illustrates a gear pump with an integrated pressure relief valve that allows flow to recycle to the inlet if pressure is higher than a set value. This not only protects the piping system from mechanical failure, but it can also save the driver from overload.
For more information on positive displacement pumps, refer to HI’s Training at training.pumps.org.