What is a Check Valve

non return valve;check valve;control valves

 

A check valve, also known as a non-return valve or one-way valve, is a mechanical device that allows fluid or gas to flow in only one direction. It prevents backflow or reverse flow of the fluid or gas, ensuring that it flows in the intended direction. Check valves are commonly used in piping systems, pumps, compressors, and other mechanical systems to prevent damage and ensure proper operation.

 

Working of Check Valves

A check valve is a type of valve that allows fluid or gas to flow in one direction only. It is designed to prevent backflow or reverse flow of the fluid or gas. The valve opens automatically when the fluid or gas flows in the correct direction and closes when there is backflow or reverse flow. Check valves are commonly used in plumbing, heating, ventilation, and air conditioning systems, as well as in industrial and manufacturing applications.

 

Types of Check Valves

Depending on the movement of the closure member, various types of check valves are available.

 

Swing Check Valve

Wafer Check Valve

Spring Loaded Check Valves

Ball Check Valves

Diaphragm check valves

Lift check valve

Stop check valve

Foot Valve

Duckbill Valve

Non-Slam Check Valve

Dual Plate Check Valve

 

 

Swing Check Valve

A swing check valve is the most widely used check valve. The closing member or the disc swings on a hinge or shaft. To allow the flow, the disc swings off the seat and swings back onto the seat to block the reverse flow. In an open position, a swing check valve offers very little resistance to the flow. To achieve optimum performance, often a lever and weight or a lever and spring are mounted. The disc weight and the return flow have an impact on the shut-off characteristics of the valve. Swing Check Valve is also known as the Tilting Disc Check valve.The swing check valve allows full, unobstructed flow and automatically closes once pressure decreases.

 

Wafer Check Valve

Wafer check valves are very slim and compact in design and use a swinging disc to allow or block flow. They are lightweight and suitable for various applications. They are economical and are available in various sizes. The following figure shows the typical working of a Wafer Check Valve.Wafer check valves are ideal for services requiring low-pressure loss as the valve operation takes place at a very low-pressure difference.

 

 

Spring Loaded Check Valves

There are two types of Spring Loaded Check Valves; Spring Loaded in-line valves and Spring loaded Y-valves.

In-line valves are also known as Nozzle Check Valves or Silent Check Valves.   These valves employ a centrally guided stem-disc assembly along with a compression spring. To open the valve, the flow pressure must be more than the spring force and cracking pressure. In that case, the flow pushes the disc allowing the flow. When the inlet pressure reduces, the spring pushes the disc against the orifice and shut the valve.

The operating principle of Spring-loaded y-check valves is similar to in-line check valves. The only difference is that the spring and movable disc are located at an angle to form a ‘y’ shape. The main advantage of Y-type check valves is that they can be inspected and serviced while the valve is still connected to the system.

 

 

Ball Check Valves

Ball check valves are simple in operation and commonly used on small pumps and in low-head systems. Ball check valves involve a spring-loaded or free-floating spherical ball clapper to shut at pressures below the cracking pressure. In order to guide the ball into the seat and create a positive seal, the sealing seat is conically tapered. However, these valves can easily wear due to prolonged use and require frequent maintenance.

 

 

 

Diaphragm check valves

Diaphragm check valves consist of rubber flexing diaphragms or self-centering discs for preventing backflow. When the inlet pressure is increased, the diaphragm flexes open, and flow starts. There are two types of diaphragm check valves;

Free-floating Normally Open Valve and

Fixed Flexing Normally closed Valve.

In the case of normally open diaphragm valves, no cracking pressure is required as the self-centering elastomeric diaphragm is free-floating. However, they need back pressure to close the valve. On the other hand, normally closed valves need a certain inlet pressure to overcome the elasticity of the fixed diaphragm.Due to very low cracking pressure, Diaphragm check valves find their use in low-pressure and vacuum applications.

 

 

 

Lift check valve

A lift check valve is also known as a piston check valve. It consists of a guided disc that raises (lifts) up from the valve seat and creates space for media to flow. The inlet pressure must be more than the cracking pressure to overcome gravity and/or a spring force. The valve will close when the inlet pressure decreases below the cracking pressure or there is back pressure.

 

 

 

Stop check valve

A stop-check valve is basically, two valves built into one body. It can act as a globe valve for isolation or regulation purposes. Again, It can act as a check valve to prevent backflow. Contrary to other check valves, the Stop check valve has an additional external control mechanism in a perpendicular or angular direction. Stop Check valves are popular in steam services like power plants, boiler circulation, steam generators, turbine cooling, and safety systems.

 

 

 

Foot Valve

A foot valve is a check valve that has a strainer installed on the inlet side to prevent debris from entering the valve.

 

Duckbill Valve

Duckbill Check Valves are unique, one-piece, elastomeric components that enable flow to proceed through a soft tube that feeds into the downstream side of the valve wherein back pressure collapses the tube and cuts off the flow.

 

Non-Slam Check Valve

Non-slam check valves are specifically designed valves where the closing member close without

slamming preventing excess pressure spikes. The disc of a non-slam check valve includes an internal spring opposing the opening fluid flow pressure. When the flow media is strong enough, the spring compresses and the valve opens. Again when the flow decreases, the disc is smoothly pushed back toward the valve seating surface by the spring force and stops. For vertical piping runs or complex applications requiring constant and controllable pressure levels, Non-slam check valves are an ideal solution.The main advantage of non-slam check valves is their ability to effectively prevent water hammer. Hence, pressure swings, vibrations, and component damages are ideally eliminated. As Non-slam valves have a short

stroke, they facilitate quick soft closing of the disc to prevent water hammer. As they consist of only one moving part, the disc itself, non-slam check valves experience minimal wear over time. However, the non-slam check valves are not piggable.

 

 

Dual Plate Check Valve

Dual-plate check valves are wafer-type compact valves with a small overall length. They provide excellent hydrodynamic properties that result in very low-pressure losses and they are technically efficient. Their low weight provides advantages during installation, transport, and storage. Dual-Plate check valves are suitable for liquid, gas, steam, condensate, water supply, and in oil and natural gas services. They are designed as non-slam types. With suitable springs, they can be installed in any position.

 

 

Applications of Check valves

Check valves are used in various industries like Offshore Oil & Gas Production, Onshore Oil & Gas Production, Gas Plant, LNG, Liquid Gases, Refineries, Petrochemical, Chemical, Fertilizer, Terminals, Pipelines, Power, Desalination, Water, etc. They are widely used in Pump and Compressor discharge, Heat Exchangers, Reactors, Vessels, and Separators to prevent flow reversal.

 

Samson Flow is a professional production, modern management, rigorous enterprise style, extensive application experience, innovative product technology and our professional service team. These factors not only ensure that we can calmly deal with the complex, diverse and harsh environmental fields of the valve industry, but also guarantee that we can provide users with system solutions from valve selection to high-quality product manufacturing and professional after-sales service.