Check Valve Selection and Sizing for Pump Discharge

Check valves on pump discharge lines prevent reverse flow when pumps stop, protecting pumps from reverse rotation, preventing water hammer from reverse surge, and maintaining system pressurization. Correct check valve selection and sizing is critical because undersized check valves cause excessive pressure drop and reduce pump efficiency, while oversized check valves chatter (flutter) at low flow rates, causing rapid wear of the disc and seat. Pump discharge check valve selection must match the check valve characteristics to the pump operating profile and system hydraulics.

Check Valve Types for Pump Discharge Service

Swing check valves are the traditional choice for large-diameter pump discharge lines because of their full-bore opening, low pressure drop, and simple design. However, swing checks are slow to close—the disc must travel through a full arc before seating—which allows reverse flow to develop before the valve closes. In systems susceptible to water hammer, this reverse flow causes a pressure surge when the disc finally seats. Tilting disc check valves have a reduced disc travel arc that allows faster closure and lower slam potential. Dual plate (wafer) check valves close very quickly due to their lightweight spring-loaded dual plates and are widely used in medium to large pump systems where slam resistance is important.

• Swing check: low pressure drop, simple, slow closure, risk of slam

• Tilting disc: faster closure than swing, moderate pressure drop

• Dual plate (wafer): fast spring-assisted closure, compact, slam-resistant

• Lift check (globe type): positive spring closure, higher pressure drop, for vertical lines

• Non-slam check: designed for very fast silent closure, used on high-inertia pump systems

Sizing Check Valves for Stable Operation

Check valves must be sized so that the disc is fully open and stable at normal operating flow velocity. A disc that is not fully open flutters against the stop, causing rapid wear and eventual disc failure. For swing check valves, the minimum velocity to hold the disc fully open is typically 3 m/s (10 ft/s) for water. If system flow velocity is below this minimum, a smaller check valve (higher velocity) should be selected, or a spring-loaded design used. Manufacturers publish minimum recommended velocities for stable disc operation. For systems with widely varying flow rates, a spring-loaded check valve maintains positive closure force at low flows, preventing disc flutter.

Water Hammer Prevention and Check Valve Selection

Water hammer (hydraulic transient) occurs when the check valve disc slams shut after reverse flow has developed, causing a high-pressure surge wave that travels through the piping. The severity of water hammer depends on the reverse flow velocity at the moment of disc closure. Non-slam check valves prevent water hammer by closing quickly (before significant reverse flow develops) or by using a controlled closure mechanism that limits the closing velocity of the disc. For critical pumping systems with high static head or long discharge lines, a hydraulic analysis of the pump trip transient should be performed to verify that the selected check valve provides adequate protection against water hammer.