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Nozzle Check Valve

May 28, 2022

What is a nozzle check valve?

A nozzle check valve is a type of valve used to prevent reverse fluid flow and also prevent water hammer and related effects. Nozzle check valve manufacturers design these valves for applications in which liquid, gas, or slurry media can be transferred. Nozzle check valves are meant to close quietly and quickly when the pressure reduces or at no-fluid flow. As such, they help prevent the flowing media from flowing in the reverse direction. Nozzle check valve manufacturers design these valves to operate automatically. This means that the valves do not need a valve actuator or a valve handwheel. These valves operate on the principle of pressure difference that is the incoming suction pressure opens the valve disc and when the suction pressure reduces it forces the disc to close automatically. Nozzle check valves are used in various fluid applications ranging from low to high temperature and from corrosive to non-corrosive fluids. 

Nozzle check valve

Figure: Nozzle check valve.

 

Components of a nozzle check valve 

Valve body 

This is the part of a nozzle check valve used to cover internal parts. Nozzle check valve manufacturers design the valve body using strong metallic materials that can withstand high pressure and high temperatures. Also, such materials prevent internal parts from impact damage when the valve falls down or in case of falling objects. Some of the strong metallic materials which nozzle check valve manufacturers use to make valve bodies include stainless steel, ductile iron, carbon steel, cast iron, and brass among others. 

Disc 

This is the part of a nozzle check valve that is used to open and close the fluid flow. The closure of fluid flow is meant to prevent reverse flow.

Spring 

The spring is used to aid the disc in opening and closing. It opens when the suction fluid pressure exceeds its force compressing it and thus moving the disc to open the valve. The design strength of the spring depends on the amount of fluid flow expected through the valve. 

Seat 

This is a component mounted between the valve disc and valve body to prevent fluid leakage as well as provide the surface where the valve disc seals. The material used to construct the seat determines its area of application. Some materials are meant for low temperature while others are meant for high temperature.

Gasket 

This is a component used in nozzle check valves to prevent leakage between the valve and pipe connection. 

Components of a nozzle check valve

Figure: Components of a nozzle check valve.

 

How does a nozzle check valve work? 

A nozzle check valve closes and opens using the disc component. The disc is assisted by a helical valve spring which gets compressed when there is high suction fluid pressure relative to the outlet pressure. The spring compresses due to the high suction pressure and since it is connected to the disc it forces the disc to move forward leaving space for the fluid to flow. As long as the suction fluid pressure remains high relative to the outlet pressure, the fluid keeps flowing through the nozzle check valve. However, any time the suction pressure starts reducing, the spring and disc start reverting slowly since the force holding the spring at a position depends on the amount of suction fluid pressure. Because of their design, nozzle check valves prevent water hammer as they prevent reverse fluid flow simultaneously. Nozzle check valves are very important in different applications like in mixing processes where components need to be maintained at precise percentages like ethanol-additive blending in which precise reverse flow prevention is very important. 

 

Types of nozzle check valves 

Threaded end nozzle check valve 

This is a nozzle check valve that is connected to the pipe by using threads. The nozzle check valve manufacturer produces this type of valve with threads on both sides of the valve ports. The pipe ends to be connected to the nozzle check valve are also produced with threads. If the threaded end nozzle check has male threads, the pipe should have female threads. This helps to ensure that the valve-pipe connection is tight enough to ensure zero fluid leakage. Threaded end check valves are recommended for use in low and medium-pressure applications. These valves are light in weight relative to bolted valves. Also, threaded end nozzle check valves occupy less space relative to bolted types. 

Figure: Threaded end nozzle check valve.

Flanged end nozzle check valve 

This is a nozzle check valve that is connected to the pipe using bolts and nuts. The bolts and nuts on this valve are mounted through holes in the valve. As such, nozzle check valve manufacturers design these valves with flanges. The flanges act as the mating faces and also it is where the holes are made. Both the valve and the pipe have the same size flanges and holes. Flanged end nozzle check valve manufacturers design these valves for use in high-pressure applications because the bolt connection and use of gasket guarantee tight seal with zero leakage. One of the challenges of flanged end nozzle check valves is that they are heavier relative to the threaded end types. The heavyweight arises from the use of bolts and nuts and additional flanges.

Flanged end nozzle check valves

Figure: Flanged end nozzle check valves.

Welded end nozzle check valve 

This is a nozzle check valve that is connected to the pipe using welding. This means that the valve and the pipe are welded together. This type of nozzle check valve becomes very essential when used to transport hazardous fluids like acids, oil and gas in which any slight leakage can be disastrous. The welding method ensures that the valve and pipe are fully intact without any slight holes. However, this type of valve is very hard to repair due to the weld. Nozzle check valve manufacturers recommend this valve for use in applications where frequent inspection and repair are not necessary. 

Plastic nozzle check valve 

This is a nozzle check valve that is made of plastic material. Such materials that can be used to make this type of valve include polyvinyl chloride and propylene. A plastic nozzle check valve is very light in weight relative to the metallic one. This is because plastic materials have low density, unlike metallic materials. The density is the key factor in raising the weight of the valve. Plastic nozzle check valves are used in low temperature and pressure applications. Plastic materials are cheap relative to metallic ones which make these valves relatively cheaper than the metallic ones. 

 

Factors to consider when selecting a nozzle check valve 

Type of media 

Nozzle check valve manufacturers design these valves with specific materials that can work in a certain type of media. Certain materials work very well in corrosive media like acids. Such materials suitable for use in acidic applications are plastics. Other materials like steel are also resistant to corrosion but not very resistant as plastics. If the nozzle check valve is used for the wrong media its service life will be very short and also expensive to maintain since internal parts will be wearing out very fast. 

Working pressure and temperature 

Nozzle check valve manufacturers design these valves to work at a certain range of pressure. Using these valves for very high-pressure levels may cause fluid leakage. Also, if the valve is used for very low pressure the fluid may not be able to open the valve and there will be no fluid flow through the nozzle check valve. Also, nozzle check valve manufacturers indicate the working fluid temperature of that valve. Very high temperatures beyond the manufacturer’s specifications can damage internal parts of the valve like discs, seals, O-rings, and gaskets. Also, high temperature may make the valve internal parts to react with the fluid being conveyed.

Flow conditions 

This is the case where the valve is made for use at a certain level of fluid flow rate and fluid viscosity. Very high fluid velocity than the range given by the nozzle check valve manufacturer may cause vibration and or loud noise. Very viscous fluid may not be able to flow through the nozzle check valve. So the valve should be used according to the instructions given by the nozzle check valve manufacturer. It would be necessary to provide the manufacturer or supplier with the flow conditions, pressure, temperature, and media type to advise on the best nozzle check valve.

 

Applications of nozzle check valves 

  • Nozzle check valves are used in chemical industries. 
  • They are used in wastewater treatment applications. 
  • They are used in food and beverage processing. 
  • They are used in domestic water supply systems. 
  • Nozzle check valves are used to prevent reverse fluid flow in boilers. 
  • These valves are used in oil and gas applications. 

 

Advantages of nozzle check valves 

  • These valves prevent water hammer and related effects. 
  • They do not allow reverse fluid flow. 
  • Nozzle check valves operate automatically.
  • These valves are versatile because they are used in different applications. 
  • They are free from fluid leakage. 
  • Nozzle check valves have low-pressure drop which helps to improve pumping efficiency.
  • Nozzle check valves can be installed in either vertical or horizontal positions. 
  • The design of nozzle check valves helps them to maintain working pressure. 
  • These valves have a quick and dynamic response to velocity and pressure changes which helps them operate faster unlike other valves like gate valve

 

Disadvantages of nozzle check valves 

  • Fluid flow in nozzle check valves takes place in one direction only. 
  • Nozzle check valves cannot be inspected while in operation. 

 

Troubleshooting nozzle check valves 

Nozzle check valve vibrates or chatters 

  • High velocity. Ensure the fluid flow velocity is as recommended by the nozzle check valve manufacturer. 

Internal fluid leakage 

  • Worn out or damaged seating surfaces. Replace the seating surfaces. 
  • Debris clogged the valves. Remove debris inside the nozzle check valve. 
  • Worn out O-rings. Replace the O-rings.

No fluid flow through the nozzle check valve 

  • The valve was installed in the wrong direction. Install the valve according to the nozzle check valve manufacturer’s direction shown in the user manual or on the valve body. 
  • The pipe transferring fluid to the valve is blocked. Check the valve for any material causing blockage and remove them. 
  • The downstream valve is closed. Ensure the downstream valve is open. 
  • Low suction pressure. Increase the suction pressure to the level given by the nozzle check valve manufacturer. 

Valve does not close 

  • The valve disc or spring has been stuck by solid particles. Open the nozzle check valve and remove any material holding the spring or valve disc. 

Fluid leakage through the valve-pipe connection 

  • Worn out gasket. Replace the gasket. 
  • Loose connection. Tighten the connecting elements that are the bolts or screws. 

 

Summary 

The nozzle check valve is a type of valve that is used to prevent reverse fluid flow and also prevent water hammer. This type of valve operates automatically using the pressure difference in which suction pressure has to be more than the outlet pressure. The incoming fluid provides potential energy to compress the valve spring which moves the valve disc forward allowing fluid flow. The fluid keeps flowing through the nozzle check valve until a time when the suction pressure starts reducing. At such instance, the valve spring starts returning the disc to the seating position until fluid is completely prevented from reversing while ensuring no water hammer and its related effects. Nozzle check valve manufacturers produce different types of these valves for certain industrial applications. The factors to consider when selecting a nozzle check valve include the type of media, operating pressure and temperature, and flow conditions. The various types of these valves include threaded end nozzle check valve, flanged end nozzle check valve, welded end nozzle check valve, and plastic nozzle check valve. Applications of these valves include wastewater treatment, domestic water supply, foods and beverages, chemicals, oil and gas, and boiler applications among others. Advantages of using nozzle check valves are automatic operation, no reverse fluid flow, high efficiency, and ability to maintain flow pressure, no water hammer, and zero leakage.

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