What is a silent check valve?
A silent check valve is a valve used to prevent reverse fluid flow. Also, this valve helps to prevent water hammer problems and its related effects. A water hammer is a shock wave of high pressure that occurs when fluid flow is stopped abruptly due to either the valve disc closing or the pump shutting down. Water hammer is dangerous because it causes high stress on the piping system which could cause structural damage to the piping system. As such, silent check valve manufacturers design these valves to help in eliminating water hammer problems. When the pump is shut off or when fluid pressure reduces, the valve has a spring action that helps to control disc closure before fluid reverses. This design helps to ensure that the valve does not slam shut and thus eliminates the water hammer and reverse fluid flow.
Figure: Silent check valve.
Components of a silent check valve
This is the part of a silent check valve used to house all the internal parts. The body is usually made very strong since it serves as the main pressure barrier as well as protecting internal parts against impact damage. To make sure the body is strong, silent check valve manufacturers use strong metallic materials to make the body. Such materials include stainless steel, carbon steel, ductile iron, and cast iron, among other metallic materials. The valve body also contains the valve ports where the fluid flows through the valve while coming from the pipe. The body also contains threads or holes for connecting it to the pipe using screws or bolts and nuts.
This is part of a silent check valve that is tasked with opening and closing the fluid flow depending on the pressure level.
A spring is used to help in returning the disc to the seating position after the flowing fluid pressure reduces. The spring employs its compressive properties to help the disc open fluid flow.
This is a component inside the body of a silent check valve that comes into contact with the valve disc as it tries to restrict fluid flow. The seat serves as a seal to prevent fluid leakage between the disc and the valve body.
This is a component of a silent check valve that is placed between the valve and the pipe to prevent fluid leakage through the connection. The gasket is held in place by the pressure created when the valve and pipe are connected using screws or bolts. There are different types of gaskets used in silent check valves which include steel, durometers, and elastomers.
Figure: Components of a silent check valve.
How does a silent check valve work?
A silent check valve works based on the principle of differential pressure. In this case, the valve opens if the upstream pressure is more than the downstream pressure. The valve closes when the downstream pressure is more than the upstream pressure. So, for a silent check valve to open, the suction pressure is high enough to provide pressure energy. The pressure energy of the flowing fluid provides the force used to compress the valve spring. Compressing the valve spring forces the valve disc to open allowing fluid flow. The fluid keeps flowing while the valve is open and the pressure remains high. When the pressure reduces the valve spring uses its potential energy to revert to its length and in that instance, it forces the valve disc to close. For a silent check valve, the fluid flow starts closing immediately after suction pressure starts reducing. As such, the valve starts closing slowly which helps to eliminate the water hammer problem. Silent check valves do not rely on gravitational force to close like lift check valves. The opening of this valve depends on the suction pressure level from the pump while closing the valve depends on compressive strength and thus potential energy associated with the compressed spring. As such, a silent check valve can be installed in vertical or horizontal direction as either orientation will not affect its working principle.
Figure: Working of a silent check valve in open and close state.
Types of silent check valves
Flanged end silent check valve
This is a silent check valve that is designed with flanges for connecting to the piping system. The flanged ends are mounted on both ends and they have holes. The holes are used to hold bolts that are used to connect the valve and the pipe. Flanged end silent check valve manufacturers recommend these valves for use in high-pressure applications. This property is enhanced by the tight seal created by connecting the valve and the pipe using bolts and nuts. Also, a gasket is placed between the two flanged ends to aid in enhancing a tight seal despite high pressure. Flanged end silent check valves are easy to assemble, disassemble and install. These valves are very strong and they can be used in high and low temperatures depending on the material of the internal parts. However, flanged end silent check valves are heavier, expensive, and larger relative to other valve types.
Figure: Flanged end silent check valve.
Threaded end silent check valve
This is a silent check valve that is connected to the pipe using threads. The pipe to be connected to the valve also has threads at the ends. The threads are either male or female. When the silent check valve manufacturer produces the valve with male threads, the pipe to be connected to the valve needs to have female threads and vice versa. Threaded end silent check valves occupy less space compared to the flanged end types. Also, these valves are light in weight and cheaper relative to the flanged ones. However, the threaded end silent check valve manufacturers recommend these valves for use in low and medium-pressure applications. These valves can be used in both low and high temperatures depending on the materials of construction.
Figure: Threaded end silent check valve.
Plastic silent check valve
This is a silent check valve that is made of plastic materials such as propylene (PP) and polyvinyl chloride (PVC). Silent check valve manufacturers design these valves for use in low-temperature and low-pressure applications. This is because plastic materials cannot withstand high temperatures due to their low melting point. However, plastic materials are cheaper relative to metallic materials and this makes plastic silent check valves cheaper relative to those made of metallic materials. These valves have good strength that helps to prevent them against impact damage from falling objects. Also, plastic materials have a low density which helps to reduce the weight of the valve. Plastic silent check valves work on the same principle of pressure difference whereby the valve opens when the suction pressure is high and closes when the suction pressure starts reducing ensuring the valve does not experience a water hammer.
Figure: Plastic silent check valve.
Casted silent check valve
This is a silent check valve that is made through the casting method. This method helps to make different types of silent check valves unlike other methods like forging. This is because all materials used to make valves can be used to produce valves using casting methods. The method of casting valves involves heating the raw materials to high temperatures until the material melts down. The molten materials are poured into a mold to give it time to cool and solidify where it makes the silent check valve of the required shape and size. The valve is also taken through non-destructive tests to ensure it has no defects which may cause malfunction and fluid leakage while in operation. Casted silent check valves are cheaper to make relative to the forged ones because the labor involved is less.
Forged silent check valve
This is a silent check valve that is made using the forging method. Some of the materials used to make forged silent check valves include stainless steel and ductile iron. The material used to make these valves needs to have some degree of ductility to ensure the material does not break while it is being worked on. The forging process involves heating the material to make it easier to shape. The material is then taken to mechanical pressing machines to form the required shape and size of the valve. These valves are very strong for use in high-pressure and high-temperature applications. However, silent check valve manufacturers use a lot of labor to make these valves which makes them quite expensive relative to other valves.
Applications of silent check valves
- Silent check valves are used in water treatment and water supply applications.
- These valves are used in oil and gas refinery and transmission systems.
- They are used in chemical processing industries.
- Silent check valves are used in steam power generation plants.
- These valves are used in pharmaceutical applications.
- They are used in the paper and pulp industries.
- Silent check valves are used in research or testing applications.
Advantages of silent check valves
- Silent check valves can be installed in either vertical or horizontal orientation since they do not depend on gravity to open or close.
- Silent check valves are automatic.
- These valves are free from fluid leakage.
- Silent check valves are free from water hammer, vibrations, and surge problems.
- They can maintain working pressure.
- They have a low-pressure drop, unlike other valves.
- Silent check valves are versatile as they can be used in different industries.
- They are durable since they can be repaired when they break down.
- They are easy to install, assemble and repair.
Disadvantages of silent check valves
- These valves cannot work in applications with pulsations fluid flow.
- Silent check valves cannot allow fluid flow in both directions.
Troubleshooting silent check valve
The silent check valve vibrates or chatters
- The fluid is moving at high velocity. Ensure the flow rate is as recommended by the silent check valve manufacturer.
Silent check valve leaking fluid
- Foreign materials are clogging the valve. Open the valve and remove any foreign materials.
- The valve seat is damaged. Replace the valve seat.
- The valve gasket is worn out or damaged. Replace the gasket.
- Loose connection between the valve and the pipe. Tighten the connecting elements that are bolts and nuts or screws to the torque recommended by the silent check valve manufacturer.
No fluid flows through the silent check valve
- The valve was installed in the wrong direction. Reinstall the valve according to the flow direction indicated by the silent check valve manufacturer.
Silent check valves are valves that are used to prevent reverse fluid flow and at the same time prevent water hammer from occurring. These valves operate automatically without the use of a valve control mechanism. Silent check valve manufacturers produce different varieties of these valves for use in different applications ranging from corrosive, low and high pressure, and temperatures. Unlike other check valves, silent check valves are best known for protecting the piping system from damage because the working mechanism is such that the valve closes slowly which helps to prevent vibration and water hammer. The valve is designed with a spring which is meant to help in closing the valve immediately after the suction pressure starts reducing or when the pump pressure starts reducing. The silent check valve opens when the suction pressure is more than the outlet pressure. Any time fluid attempts to flow back the valve disc assisted by the spring closes restricting reverse fluid flow. Silent check valve manufacturers produce various types of valves such as threaded end silent check valves, flanged end silent check valves, plastic silent check valves, forged silent check valves, and cast silent check valves among others. These valves are used in different industries such as water supply and treatment, oil and gas, chemicals, pharmaceuticals, foods and beverages, steam power plants, and mining applications among others. Advantages of using a silent check valve are versatility, long durability, zero fluid leakage, automatic, no water hammer, low-pressure drop, and ability to maintain working pressure.