Single Check Valve

What is a single check valve? 

This is a check valve designed with a thin plate at its middle section. This type of valve is used to prevent reverse or backflow of fluid. A single check valve operates automatically using pressure differential and thus it saves on the cost of having a valve actuator and or handwheel. This helps to cut down its manufacturing cost. Single check valve manufacturers follow certain design standards such as ASME B16.34 among others to design this type of valve. These standards help to ensure a quality valve suitable for use in different industrial applications. A single check valve is connected to the piping system using flanges. They held in position by using screws through flange holes. The screws help to connect the valve to the piping system to ensure a tight seal with zero leakage.  

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Figure: Single check valve.

Components of a single check valve 

Body 

This is a component of a single check valve that is used to house internal parts of the valve. The valve body is very strong to make it withstand internal fluid pressure. Also, its high strength helps to withstand impacts from falling objects or when the valve falls. The body can be made of strong metallic materials like stainless steel, carbon steel, ductile iron, and bronze among others. 

Disc/Plate 

The plate or disc is the component of a single check valve that is used to open and close the valve to allow and block fluid flow respectively. The plate can be made of various materials depending on the area of application. 

Spring 

The spring is made of metallic material to assist the disc/plate in closing the valve. Single check valve manufacturer design this valve such that the strength of the spring is proportional to the fluid pressure to ensure that the valve can open due to incoming fluid pressure and also close when fluid pressure reduces or when there is backflow. 

Seat 

The seat is the part of a single check valve that provides a seal between the valve body and the disc/plate. It helps to ensure no fluid leaks when the plate closes the valve to prevent reverse fluid flow. The properties of the seat material determine its area of application. It can be a metallic or soft seat. The soft seats are suitable for use in low temperatures while metallic seats can be used in both low and high temperatures.

Gasket 

This is a component placed between the valve flange and the pipe to enhance a tight seal free from fluid leakage. Also, the gasket material determines the area of application from high to low temperature to corrosive and non-corrosive media. 

How does a single check valve work? 

A single check valve operates by using the pressure difference principle. This is the case where the valve disc opens when the suction pressure is more than the outlet pressure. The suction pressure provides the force needed to push the plate forward by compressing the valve spring. The fluid keeps flowing through the single check valve unless the suction pressure reduces or when there is backflow. I the suction pressure reduces or there is backflow, the valve spring regains its energy to stretch back and thus it reverts the disc to the seating position. This makes the plate close fluid attempting to reverse flow direction. Single check valve manufacturers use simple design yet very essential in different applications. This type of valve helps to prevent fluid contamination such as in water supply and also prevents losses when fluid flow back into boilers or pumps. 

Types of single check valves 

Bronze single check valve 

The bronze single check valve is a valve that is made of bronze material. Bronze single check valve manufacturers use the bronze material to make the whole valve or combine bronze and other materials. Other materials that can be used together with bronze to make this valve include rubber and plastics that can be used to make the valve seat. Such materials can be used for different reasons such as lower the cost of the valve considering bronze is more expensive relative to plastic. Also, it could be that the single check valve manufacturer indents to use the valve in slightly corrosive media. As such, having a bronze single check valve with a plastic seat or disc will make it suitable for use in corrosive applications. Also, such a valve can be meant for use in low-temperature applications thus no need for metallic seats. Bronze single check valves are easily identified by their color which is yellowish-brown.

Figure: Bronze single check valve.

Plastic single check valve 

This is a single check valve made of plastic materials. Plastics have a low density which makes them light in weight. This material is also more resistant to corrosive media than the metallic types. In addition, plastics have medium strength which protects them against falling objects that result in impact damage. As such, single check valve manufacturers use plastics to make the valve light in weight and also ensure the valve can be resistant to corrosion as well as be resistant to impact damage. Some of the materials that have been used to make these valves include propylene (PP) and polyvinyl chloride (PVC). However, plastic single check valves operate at low temperatures because the plastic material has a low melting temperature. Plastic single check valve manufacturers recommend using these valves where the fluid temperature does not exceed 60 ^oC.

Figure: Plastic single check valve.

Stainless steel single check valve 

This is a single check valve that is made of stainless steel material. Stainless steel material has good mechanical and thermal properties which makes this type of valve suitable for use in both low and high pressure and temperatures. Stainless steel has a very high melting temperature of around 1400 ^oC which makes it able to withstand high thermal heat. Also, the strength of this material is very high and thus it makes a stainless steel check valve very strong against pressure and impact damage that may result from falling objects. Stainless steel single check valve manufacturers use soft or metallic seats or O-rings. Soft seats and O-rings are made of soft materials like plastic or rubber. Single check valve manufacturers produce such valves for use in low temperatures. Metallic seated stainless steel single check valves are used in both low and high temperatures because they can withstand high temperatures. 

Figure: Stainless steel single check valve.

Applications of single check valve 

• Fresh water and wastewater treatment. 
• Boiler systems to prevent steam or feedwater from reversing. 
• Chemical manufacturing plants. 
• They are used in oil and gas industries. 
• Foods and beverages. 

Advantages of single check valves 

• They occupy small space relative to other valves,like ball valve and gate valve. 
• Light in weight and small in size. 
• They do not allow reverse fluid flow. 
• Low-pressure drop which improves pumping efficiency. 
• They maintain expected fluid pressure. 
• Operated automatically reducing the cost of valve actuator. 
• Cheaper relative to other valves, such as plug valve. 
• They can be used in both low and high temperatures. 
• Do not need lubrication. 
• Free from fluid leakage. 
• Operate faster relative to other valves, such as globe valve.

Disadvantages of single check valves 

• Work well in pulsating fluid flow. 
• They are prone to causing water hammer problems.
• They cannot be inspected while in use. 
• The valve cannot allow fluid flow in both directions.

Troubleshooting single check valves 

Single check valve having external leakage 

• Loose connection between the valve and the pipe. Tighten the connecting screws. 
• Worn out or damaged valve O-rings. Replace the O-rings. 

No fluid flow through the valve 

• There is low suction pressure. Increase the suction pressure. 
• Wrong valve direction of installation. Install the valve according to the arrow indicated by the single check valve manufacturer. 
• The pipe feeding the single check valve is blocked. Check the pipe and remove any particles causing a blockage. 
• The downstream valve is closed. Open the downstream valve. 

The single check valve does not close 

• The plate has been stuck open by foreign materials. Open the valve and remove foreign materials interfering with plate closure. 

Summary 

A single check valve is a type of check valve with a thin plate. The plate serves as the valve disc that is it is used to close and open fluid flow. It helps to prevent reverse fluid flow when suction pressure reduces or when there is backflow. The plate is pivoted at one end and the other end is free. The plate opens when fluid presses on the free end making it open about the pivoted point.

Single check valve manufacturers design this valve to use a spring or to work without a spring. The spring helps to revert the plate to the seat when pumping pressure reduces. The single check valves without spring depend on the backflow of the fluid to force the plate to its seating position.