Check valves allow the flow in one direction and prevents back flow in case the fluid in the line reverses direction. They are self-automated valves that do not require any operator – either manual or automatic – to open and close. That’s a plus whenever in a plant there is a loss of electricity or pneumatic air supply.
Check valves are used with a variety of process fluid : liquids, gases, steam, condensate. Applications include pump and compressor discharge, header lines, vacuum breakers, steam lines, condensate lines, chemical feed pumps, cooling towers, loading racks, nitrogen purge lines, boilers, HVAC systems, utilities, pressure pumps, sump pumps, wash-down stations, and injection lines.
Check valves like piston check valves or swing check valves are flow sensitive and rely on the line fluid to open and close. The internal disc allows flow to pass forward, which opens the valve. The disc begins closing when flow decreases or is reversed. If there is not enough flow, disc movement occurs inside the valve since the disc is always in the flow path. This results in wear, potential for failure, and a higher pressure drop than calculated. Typically, pressure drop is calculated based on the check valve being 100% open, as with on/off valves. However, if the flow is not sufficient to achieve full opening and the check valve is only partially open, the pressure drop will be greater than calculated since the flow passage is restricted by the disc being in the flow path. In this situation, a large-rated Cv actually becomes detrimental to the check valve (unlike with on/off valves), resulting in fluttering of the disc and eventual failure. Such is not the case with some other valves. With a gate valve, for example, if the valve is fully open, the wedge is out of the flow path and the flow through the valve does not affect the performance of the wedge whether that flow is low, medium, or high.
Construction is normally simple with only a few components such as the body, seat, disc, and cover. Internal sealing of check valves disc and seat relies on fluid back-pressure as opposed to the mechanical force used for on-off valves. Metal sealing surfaces generally allow some leakage while elastomers, such as Buna-N and Viton, provide bubble-tight shutoff (zero leakage). Because of this, elastomers should be considered for air/gas media, where chemically compatible, and low-pressure sealing.
Among the many factors to consider when selecting a check valve are material compatibility with the medium, the valve rating, the fluid velocity given by yhe valve size, the operating conditions, and finally the installation (horizontal or vertical).
There are many different check valves design, at MAGVALVES we deal with piston check valves and swing check valves.
Design: Swing check, Ball check (straight or Y pattern), Piston check (straight or Y pattern), Tilting disc, Dual plate, Axial
Construction: Bolted Cover, Welded Cover, Pressure Seal
Main Design Codes: ASME B16.34, API 602, BS5352, ISO 15761, API 6A, BS 1868
Pressure Class: ANSI 150#-4500#
Size Range: from ½” to 24”
API 6A Pressure Class: 3000-15000
API 6A Size Range: from 1.13/16” to 11”
Ends: SW, NPT, BW, RF, RJ, HUB, Compact Flange
Material: Carbon steel, Stainless steel, Alloy steel
Alternative customized solutions can be provided
Including: design for cryogenic service /vertical ball check without spring