BM Engineering Supplies guide to non-return valves
In this article, PIF spoke to leading Scottish valve distributors, BM Engineering Supplies, about one of the most popular check valve types within the Scottish process industry; the non-return valve (NRVs). Here, we discover the different types of non-return valve types, as well as their specific functions and advantages.
What is a non-return valve?
A non-return valve allows fluid to flow through them in one direction only, hence why they are commonly referred to as one-way valves. NRVs are also a type of two-port valve as they feature two openings in the body; one for fluids to enter and the other for them to leave. Non-return valves typically work automatically, meaning they do not require to be operated manually by a person or external control. As such, most NRVs do not feature handles or stems.
Why use non-return valves?
Available in a wide range of sizes, non-return valves are generally small, simple and inexpensive. They also protect pumps and compressor equipment from any potential damages which might b caused by either backflow or reverse flow. NRVs can reduce downtime and loss of production within the process industry due to the failures of incompatible valves. Non-return valves also present notable energy-saving opportunities for manufacturers within the process industry, thanks to their low-pressure drops and effectiveness in preventing water hammer. With the added functionality of reducing both possible valve failure and reducing maintenance costs due to fewer moving parts, it’s unsurprising to understand their growing popularity within the process industry.
Non-return valve types
Having provided PIF with a comprehensive understanding about the working principle of non-return valves and the benefits they afford users, we asked Scott Miller of BM Engineering Supplies to enhance our knowledge further by breaking down the different types of non-return valves available to purchase from UK valve distributors and suppliers:
Ball non-return valves
“Ball NRVs feature a closing member (a moveable part) to block the flow of fluids (that is a spherical ball)” says Scott. “This is sometimes spring-loaded to help keep it shut, or otherwise, reverse flow is required to move the ball toward the seat and create a seal”. The interior surface of the main seats of ball non-return valves is conically tapered to guide the ball into the seat and form a positive seal when stopping reverse flow. Bal NRVs are often preferred by process manufacturers as they often very small, simple and cheap.
Diaphragm non-return valves
“Diaphragm NRVs use a flexible rubber diaphragm to create a normally closed valve”, continues Scott. “Pressure on the upstream side must be greater than the pressure on the downstream side (pressure differential) for the diagram non-return valve to open and allow flow to pass through”. Once the positive pressure stops, the diaphragm automatically flexes back to its original closed position.
Swing check non-return valves
“Swing check NRVs feature a moveable part that blocks flow which swings on either a hinge or trunnion on to the seat to block reverse flow or off the seat to allow forward flow”, explains Scott. “The seat opening cross-section may be perpendicular to the centerline between the two ports or at an angle”. Although swing check non-return valves come in a variety of sizes, most large NRVs preferred by manufacturers are often the swing check variant.
Stop check non-return valves
“Stop check NRVs have an override control to stop the flow, regardless of flow direction or pressure”, discusses Scott. “As well as closing in response to insufficient forward pressure or backflow, stop check non-return valves can also be deliberately shut off by an external mechanism”.
Lift check non-return valves
“Lift check NRVs feature a disc (sometimes called a lift), which can be lifted off its seat by higher pressure of inlet or upstream fluid to allow flow to the outlet or downstream side”, continues Scott. “When the pressure drops, gravity or higher downstream pressure causes the disc to the lower onto its seat, shutting the lift check non-return valve to stop reverse flow”.
In-line non-return valves
“In-line NRV’s are similar to lift check NRV’s but generally feature springs that lift when pressure is on the upstream side of the valve”, explains Scott. “The pressure needed on the upstream side to overcome the spring tension is referred to as the ‘cracking pressure’. When the pressure goes below the cracking pressure, the spring will close the in-line non-return valve to prevent back-flow”.
Buy non-return valves from BM Engineering Supplies
As trusted valve suppliers to Scotland’s process industry, BM Engineering Supplies has one of the most extensive industrial valve ranges of any Scottish valve distributor. To learn more about BM Engineering’s non-return valves, visit their website.
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