Check Valves

Check valves are self-activating safety valves that permit gases and liquids to flow in only one direction, preventing process flow from reversing. They are classified as one-way directional valves. Fluid flow in the desired direction opens the valve, while backflow forces the valve closed. The mechanics of check valve operation are relatively simple. Most check valves contain a ball that sits freely above the seat, which has only one through-hole. The ball has a slightly larger diameter than that of the through-hole. When the pressure behind the seat exceeds that above the ball, liquid is allowed to flow through the valve; however, once the pressure above the ball exceeds the pressure below the seat, the ball returns to rest in the seat, forming a seal that prevents backflow.

Check valves use a variety of technologies to allow and stop the flow of liquids and gases. Single-disc swing valves are designed with the closure element attached to the top of the cap. Double-disc or wafer check-valves consist of two half-circle disks hinged together that fold together upon positive flow and retract to a full-circle to close against reverse flow. Lift-check valves feature a guided disc. Spring-loaded devices can be mounted vertically or horizontally. Silent or center guide valves are similar to lift check valves, with a center guide extending from inlet to outlet ports. The valve stopper is spring and bushing actuated to keep the movement "quiet.” Ball check valves use a free-floating or spring loaded ball resting in a seat ring as the closure element. Cone check valves use a free-floating or spring loaded cone resting in the seat ring as the closure element.

Selecting check valves requires an analysis of performance specifications, materials of construction, connection types, and media. Performance specifications include valve size, pressure rating, media temperature, and valve flow coefficient. Most check valves are made of acetal polymers, aluminum, brass, bronze, cast iron, chlorinated polyvinyl chloride (CPC), ductile iron, copper, polyethylene (PE), polypropylene (PP), polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), rubber, steel, or stainless steel. Connections for check valves can use threads, compression fittings, tube fittings, bolt flanges, clamp flanges, butt welds, socket welds, and union connections. In terms of media, check valves are rated for air, compressed air, water, hot water, cold water, potable water, salt water, wastewater, gasoline, diesel fuel, high-purity gas, liquefied petroleum gas (LPG), natural gas, sour gas, corrosive gas, abrasive material, acids, corrosive chemicals, adhesives, concrete, grout, coolants, hazardous materials, high-viscosity fluids, hydraulic fluids, liquid metal, lubricants, oil, powders, solids, rendering wastes, sludge, slurry, ash slurry, or steam.

• Guide for the Selection, Installation and Maintenance of Silent Check Valves
  Experience has proven the need for check valves in piping where reverse flow could be detrimental to the system. A valve which closes quietly and eliminates water hammer is obviously desirable. A need...
  (read more)
• Technical Bulletin: PUR-GasTM Purifier System
  Point-of-use, high-performance gas purifier system designed to provide superior contaminant reduction and utilizes removable purifier cartridges to produce 99.9999% purity. The basic system consists...
  (read more)
• A Reliable Liquid Fuel System (.pdf)
  Correct component selection can overcome problems in the functioning of liquid fuel systems in dual-fuel gas turbines. Using the appropriate liquid fuel, purge air and water injection check valves...
  (read more)

Pages: 1 - 3 of 467

Part Numbers for Check Valves