Check valves, also called one-way directional valves, are safety valves that allow gases and liquids to flow in a single direction. The main purpose of check valves is to prevent the flow from going in reverse direction which would otherwise cause the system or equipment to damage, partially or completely, causing a major setback.
Check valves are applicable in systems such as compressors or pumps where flow of gas or liquid in reverse direction would cause the system to shut down completely. They are also applicable in conditions where the system possesses varied pressures and they all need to be kept separately. They operate on the pressure drop created by the medium in which they reside, hence they do not require any external power supply.
Types of Check Valves
TRUPPLY offers a wide range of check valves to its customers with best prices in town. Our wide range includes:
Check valves are an important part of piping design to prevent back flow of fluids. All check valves comes with direction arrow embossed on the body to indicate the direction of flow.
Check valve types include:
Swing Check Valve
The most common type of check valve is a swing check valve. It operates by gravity. The velocity pressure of the fluid exerts a force over the area of disk and overcomes the force of gravity to unseat the disk. It is important that these valves be oriented correctly so that the disk closes itself with gravity with no fluid flow. Swing type check valves require a minimum flow to overcome the weight of check disk. Minimum flow is also required to prevent rapid opening and closure of the check to prevent chattering. Sometimes the swing check valve is kept smaller than the flow pipe to keep velocities high and avoid rapid chattering of check. For example, in a steam application the recommended velocity is 14,000 to 15,000 ft per minute.
Swing check valves pivot on a pin attached to the top of the disk, rotating the disk up and toward the edge of the flow stream. When the pressure/flow drops, the check swings back to close position.
Lift Check Valve
Lift type check valves are available in straight through, T, or WYE pattern. This type of check valve may be installed horizontally or vertically but the lift checks relying on gravity must be installed so that the disc travel is vertical.
The seat of a lift-check looks very similar to Globe type valve. The disc is either a piston or ball. Lift check valves are suitable for high pressure application where velocity of flow is high. In lift check valve design, the disc is precisely guided and seats nicely in the mating hole. Lift checks can be installed in horizontal or vertical positions as mentioned above.
Lift check valves require that flow enters below the seal. The fluid flows below the seat, the piston or ball is raised with in the guides of the valve, by the pressure of fluid. When the flow stops or reverses, the piston or ball is forced back into position by backflow or gravity.
Ball Check Valve
Ball check valves use a ball as the sealing element. These valves are always used in vertical position. The light weight ball moves away with the force of fluid and seats back with spring pressure. The seat of ball check valve is spherical and is matched to the size of the ball.
Silent Check Valve
Silent check valve is a spring-loaded straight through design. These may be constructed with a solid disk that lifts off the seat against inlet pressure or with a twin disc design that is hinged in the center of the disc.
Inline Check Valve
Inline check valves are spring loaded ball check valves with low cracking pressure. They are used on flow lines to prevent back flow and usually have a crack pressure of 2 psi. It prevents the backflow while allowing forward flow with minimum pressure. Inline check valves are low profile and are installed in horizontal or vertical position.
Q&A with a Valve Distributor
We recently sat down with a valve distributor which specializes in smaller size valves (up to 4") mainly for O&G customers. Below is the transcript of the session.
Speaker 1: This is our ductile iron check valve. It has a ductile iron body. It does have one flow one that gives you the direction of that flow right there. We do offer that in a quarter-inch, one-inch all the way up to a four-inch. We do offer 300 pound, 600 pound, 900 pound, a 1000 pound and a 2000 pound. Was I missing anything?
Speaker 2: That's in the DSCV, that's ductile iron. When you get into anything above the 2000 pound, this body will go from a ductile iron to a carbon steel. So that's it.
Speaker 3: Have you talked about all the components?
Speaker 2: Ok, so essentially you've got a flapper in here. This will be one directional; you can see the arrow. The swing check essentially is to create backflow going back to the production trees or whatever you got it in place for. So once that line becomes dead the product is going to be on the right side, the flapper falls down and then will create backflow from going backside of the line.
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Those syle of Dressor's are not easy to find out there. We used to use this style for the 2" x 1-1/2" swage pipe reducer assemblies for the reverse air-pulse system years ago with our production. We cut those Dressor Couplings in half, and weld those cut ends to the side of the steel filter housing. Of course, with the rubber ring gasket removed. Thank you Trupply for having those in stock, and also reasonably priced, too.