Non Return Valves are automatic in operation and designed to prevent reversal of flow in fluid piping systems. The valves are maintained open by the flow of fluid in the forward direction and are closed by back pressure of the fluid or by the weight of the closing mechanism or by a spring force. Various designs are available as listed below.
The range of check valve sizes range from 50mm to massive units of 1200mm dia. The swing check variation is a low pressure drop unit based on a hinged disc. This type of valve is suitable for low velocity applications with infrequent velocity reversals. The valve can be fitted with external weights to allow faster closure to reduce water hammer or shock pressure on flow reversal. External systems can also be included to force the valve closed in the event of a local fire.
The Dual Plate Check Valve employs two-spring-loaded plates hinged on a central hinge pin. When the flow decreases, the plates close by the action of torsion spring before flow reversal takes place. This design offers the twin advantages of No Water Hammer and Non Slam simultaneously. All features put together make the Dual Plate Check Valve as the most efficient & versatile design. It is also referred to as Silent check valve.