Check Valves

A check valve has no stem, no handwheel, and nothing for an operator to turn. Flow moving in the correct direction pushes a disc, flap, or plate open; the moment flow tries to reverse, that same component swings, lifts, or slides shut under its own weight or a spring, sealing the line before backflow can develop. That's the entire mechanism, and it's why check valves sit downstream of every pump and compressor discharge on a piping system: without one, a pump that trips or loses power lets the line's full head slam back through the impeller.

NLS sources three check valve types, each suited to a different install condition. Swing check valves use a hinged disc that swings clear of the flow path when open, the simplest and most common type for horizontal lines with moderate flow velocity. Lift check valves guide a disc straight up and down in line with the flow, similar in body shape to a globe valve, and handle higher-velocity or pulsating flow better than a swing type. Dual-plate (wafer) check valves use two spring-loaded half-discs in a slim body that fits between flanges, saving face-to-face length and weight on larger lines where a full swing or lift body would add unwanted bulk. All three follow API 594, the standard covering check valve design, testing, and inspection, with face-to-face and pressure-temperature ratings per ASME B16.34.

On Saudi projects, check valves go in on every pump discharge line, whether firewater, process transfer, or HVAC chilled water circulation, and on compressor discharge lines in utility plant rooms. Selecting the right type matters more than it looks: a swing check on a line with rapid flow reversal can slam shut hard enough to cause water hammer, while a spring-assisted lift or dual-plate type closes fast enough to prevent that same slam, so NLS asks for the pump curve or system's flow-reversal characteristics before confirming type on any line prone to fast shutoff.

NLS quotes check valves against a valve schedule or pump/compressor package spec and returns pricing in USD. Standard swing check valves in common cast steel and ductile iron sizes typically source faster than dual-plate types in larger diameters, which are more often built to order with a manufacturer-confirmed lead time.