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Check Valves

Check valves are typically used in pneumatic-control circuits. A check valve is sometimes referred to as a "non-return valve." These types of valves allow media flow in one direction only.

Check valves or "non-return valves" perform the same type of function that diodes perform in electronic circuits.


About Check Valves

Check valves are mechanical 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 not complicated. 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. But 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 stem the flow of liquids and gases. They are as follows: single disc swing valves, double disc swing valves, lift-check, silent, ball-check and cone-check.

Single disc swing valves are designed with the closure element attached to the top of the cap. The closure element can be pushed aside by the flow, but swings back into the close position upon flow reversal. These valves are not good choices in services with frequent flow reversal, as the disc is often pounded into the seat and wears quickly. These valves may be installed vertically or horizontally, although when mounted vertically a lever and counter-balance should be applied to reduce the valves tendency to stay open in situations where flow velocity changes slowly.

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. The valve is inserted between two flanges. These are most commonly used liquid services. Wafer valves are popular because they are generally compact and have a relatively low cost.

Lift-check valves have a disc that is guided. Spring-loaded types can operate in either vertical or horizontal mounting. The style that lacks the spring must be mounted in such a way as to allow gravity to close disc. Composition disc valves are available for gritty liquid services.

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. Upon reverse flow, the ball is forced back into its seat preventing backflow. These valves are good for most services. They can even handle fluids that produce gummy deposits. Since the disc is free to rotate wear is distributed evenly and this all helps to keep the valve seats clean.

Cone check valves use a free-floating or spring loaded cone resting in the seat ring as the closure element. Upon reverse flow, the cone is forced back into its seat preventing backflow.

Check valves are mechanical 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 not complicated. 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. But 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 stem the flow of liquids and gases. They are as follows: single disc swing check valves, double disc swing check valves, stop check valves, miniature check valves, air check valves, ball check and PVC check valves.

Single disc swing check valves are designed with the closure element attached to the top of the cap. The closure element can be pushed aside by the flow, but swings back into the close position upon flow reversal. These valves are not good choices in services with frequent flow reversal, as the disc is often pounded into the seat and wears quickly. These valves may be installed vertically or horizontally, although when mounted vertically a lever and counter-balance should be applied to reduce the valves tendency to stay open in situations where flow velocity changes slowly. 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. The valve is inserted between two flanges. These are most commonly used liquid services. Wafer valves are popular because they are generally compact and have a relatively low cost.

Ball check valves use a free-floating or spring loaded ball resting in a seat ring as the closure element. Upon reverse flow, the ball is forced back into its seat preventing backflow. These valves are good for most services. They can even handle fluids that produce gummy deposits. Since the disc is free to rotate wear is distributed evenly and this all helps to keep the valve seats clean.

Integral Fitting Check Valves

Compact and light weight, these check valves feature a built-in instant fitting. Simply push your tubing in the fitting and your non-return valve is ready to go. Both check valve and fitting are rated for compressed air only, with pressures ranging from -14.5 to 145psi. A Delrin body makes this check valve perfect for harsh ambient conditions. Prices starting under $8.00 make this fitting/valve package an unbelievable value. Integral fitting check valve sizes in stock include: 4mm, 6mm, 8mm, 5/32", 1/4" and 3/8".

NAK Series Check Valves

Series AK/AKH/AKB check valves offer various configurations to provide design solutions based on operating conditions. The series is compact and lightweight with low cracking pressure. The AKH with one-touch fitting, straight type, is easily installed in pipelines, while the male connector type can be mounted directly onto equipment. The bushing type AKB can be used in applications with splashing coolant and spatter, etc.


AKM Series Check Valves

Check valve with intermediate air release port. It can be easily installed to prevent a back flow of lubricant when redirecting the air flow. This check valve is typically used between a regulator and a lubricator to supply an unlubricated air supply. The check valve keeps lubricated air from getting into the unlubricated lines.

Miniature Check Valves

The F-2804 Series Small Check Valves permit flow in one direction only. The operation of the check valve is based on the movement of a small disc. The disc shifts within the housing as the pressure differential changes from forward to reverse. A flat surface on one side of the disc seals off flow, while the other side allows flow to pass. Two models are available from the Standard Units: F-2804-401, 402, 403, and the High-Flow Unit: F-2804-404. The advantages of the check valve design is the low "cracking pressure" minimum differential required for forward flow, which is less than the 0.005 PSI differential in the standard units. Secondly, there is no residual pressure difference across the check valve once flow has ceased. Flow in the forward direction is relatively unrestricted, approximately equivalent to the restriction of a 0.040 inch orifice in the standard units.

Bi-directional Check Valves

The BDC Series B-Directional Check Valve Permits a differential flow in both directions. The free flow direction permits flow in excess of 1,000 liters a minute. The controlled flow direction with a pressure differential of 5 PSIG or more has a flow less than 1 liter a minute. An umbrella shaped performance flow disc allows for bi-directional flow to equalize as the pressure bias across the umbrella stabilizes.


Polypropylene Check Valves

The Polypropylene Series Ball Check Valve incorporates a stainless ball that seals on a Viton o-ring seat. The Polypropylene Series Check Valve maximum operating pressure of 125 psi covers a wide range of air and fluid applications. The Polypropylene Check is a compact design with a light 1 psi cracking pressure and a positive seal at low back pressure. Nylon bodies, teflon ball checks and Hastelloy Springs are available upon request. These materials are most often used in chemically adverse conditions.