Small Check Valve

What is a small check valve? 

As the name suggests, a small check valve is a small sized valve used to prevent reverse fluid flow. Reverse fluid flow occurs in the piping system when the pump is turned off or there is backflow. Fluid flowing in the backward direction can lead to contamination or damage to the boiler and pump. Small check valves are meant for use in low and medium-pressure applications. These valves are automatic in operation. The automatic operation is enhanced by the use of pressure difference in which the valve opens when the inlet pressure is more than the outlet pressure. Small check valve manufacturers design this type of valve for use in low and high temperatures. The range of temperature the valve can be used depends on the materials used to make the valve. The use of metallic material makes the valve able to withstand high temperatures unlike the use of plastic or rubber material in which the valve is suitable for use in low-temperature applications. Small check valve manufacturer design these valves to operate using a ball or disc component as the closing member. 

Figure: Small check valve.

Components of small check valve 

Valve body 

The body of a small check valve is the main component used to house internal parts. The body is mostly made of metallic materials such as brass, bronze, carbon steel, stainless steel, ductile iron, and cast iron among others. Small check valve manufacturers use metallic materials to make the body enhance high strength against fluid pressure as well as resistance to high temperature. 

Bonnet/cover 

Bonnet is a cover placed on top of the valve body. The body and bonnet are connected using the welding method or threads/screws. Both of them are made of the same materials to enhance compatibility when tightened. The bonnet helps to contain fluid pressure and ensures no fluid leakage. 

Disc/ball 

This is part of a small check valve used to prevent reverse fluid flow. Small check valve manufacturers design the valve to have the closing member as either ball or disc depending on the type of the valve. 

Seat 

The seat is mounted between the body and the ball/disc and it is meant to provide the surface where the disc/ball settles when it closes fluid flow. Small check valve manufacturers make the seat using different materials depending on the area of application. The seat material can be metallic or soft material like plastic or rubber. 

Spring 

This is a component used to help the ball/disc to return to its seating area when the forward fluid flow stops or when there is backflow. The spring can stretch and compress as necessary. These two properties are used to help the valve open and close accordingly.

How does a small check valve work? 

A small check valve operates on the principle of pressure difference. This is a principle in which the valve disc/ball is forced to open when the upstream fluid pressure is more than the downstream fluid pressure. This scenario creates a force that acts on the ball/disc pushing it to create flow space. With the high upstream pressure, fluid keeps flowing via the small check valve. When the suction fluid pressure is reduced or the pump is turned off, the valve ball/disc is forced to revert to its closing position where it closes preventing reverse fluid flow. This ability of the disc/ball to return to the closing position is enhanced by the use of spring or by gravity or using backflow. Other small check valve manufacturers design the valve such that the disc/ball closes by using backflow and gravity without spring. The advantage of having a spring is that the small check valve can be installed in a vertical or horizontal position. 

Figure: Working of a small check valve.

Types of small check valves 

Spring loaded small check valve 

This is a small check valve that closes the valve disc/ball using a spring component. The spring works by either stretching or compressing and thus moving the ball/disc from its closing position leaving a free space for the fluid to flow. Spring loaded small check valve manufacturer design such valves with the spring being collinear, oblique, or vertical to the valve disc/ball. As such, there are three types of spring-loaded check valves which are in-line spring loaded type, Y-shaped type, and lift type. These three types work on the same principle of compressing/stretching the spring to allow fluid flow and the spring returning to its seating position when suction pressure reduces. The Y-shaped small check valve has advantages in that it can be opened for inspection and repairs without the need to remove it from the pipe connection. However, the Y-shaped spring-loaded small check occupies more space relative to the in-line type. 

Figure: Spring loaded small check valve.

Small wafer check valve 

This is a small check valve that uses a disc pivoted at one end and is used to prevent reverse fluid flow. The Disc is mounted on the valve body using an arm. The arm is hinged so that when the fluid hits the disc on the free end it can lift leaving unobstructed space for fluid flow. The small wafer type check valve can have a single or double plate. The single plate is cheaper compared to the dual plate small check valve. The dual plate small check valve uses two half discs known as plates that are supported by springs to prevent free rotation. When the fluid flows through the valve the two plates are flapped forward leaving fluid flow space. The dual plate check valve is more expensive relative to the single plate type. One advantage of the small wafer check valve is that it is slim and light in weight. 

Figure: Small wafer check valve.

Plastic check valve 

This is a small check valve that is made of plastic material. Small check valve manufacturers recommend the use of such valves in low temperatures to avoid damage by thermal heat. Small plastic check valves are easy and cheaper to manufacture compared to metallic ones. Small plastic check valves are suitable for use in low to medium-pressure applications. Because of the low density of plastic materials, these valves end up being light in weight relative to the metallic ones. Propylene and polyvinyl chloride are some of the plastic materials that are used to make small plastic check valves. However, these valves have low strength and thus they cannot withstand high pressure. Small check valve manufacturers design such valves for use in applications like water and corrosive media. This is because plastic materials are much better at resisting corrosion compared to metallic ones. 

Figure: Small plastic check valve.

Small swing check valve 

This is a small check valve that uses a flapping disc similar to a wafer type valve but this one has a bonnet supporting the body to protect internal parts. Small check valve manufacturers design this swing check valve with threads at the port ends to help connect the valve and the pipe. Small check valve manufacturers produce this valve to operate using a disc that is pivoted at one end. This leaves the other end free so that when fluid acts on it the disc opens with ease. Small swing check valves can be used for different types of media depending on the material used to make internal parts. These valves can also be used in low to high temperatures depending on the internal materials used by the small swing check valve manufacturer. 

Figure: Small swing check valve.

Double check valve 

This is a small check valve that is used to prevent reverse fluid flow in water applications. This type of valve consists of two valves that are connected in series to prevent reverse fluid flow. This type of valve is very reliable because each valve has its ball which prevents reverse fluid flow in case one valve malfunctions. The malfunction of such a valve can happen due to foreign material interfering with ball movement and thus being unable to close. Small check valve manufacturers recommend inspecting these valves quite often to ensure the valve is properly functional. This is because double check valves are used in the transportation of freshwater for human consumption and in case of any mechanical problem they may be a health hazard to people depending on them. 

Figure: Double check valve.

Applications of small check valves 

• Used in domestic and commercial freshwater supply. 
• They are used in wastewater treatment.
• Food industries. 
• Boiler applications to protect against boiler damage and reverse fluid flow. 
• Petrochemical and chemical applications. 
• These valves are used in the oil and gas industries. 

Advantages of small check valves 

• Light in weight. 
• They occupy less space.
• Cheaper.
• Do not allow reverse fluid flow but only forward fluid flow. 
• Automatically operated by employing the pressure difference principle. 
• Do not need lubrication compared to other valves like stop check valve. 
• Can be used in both low and high temperatures depending on the material used to make the valve. 
• Fast in operation.

Disadvantages of small check valves 

• Prone to water hammer problems. 
• They do not perform well in pulsating fluid flow applications. 
• Allow fluid flow in one direction only. 

Troubleshooting small check valves 

Internal fluid leakage 

• Debris inside the valve. Open the small check valve and clean any debris. 
• Damaged or worn seat. Replace the valve seat. 
• Damaged O-rings. Replace the O-rings. 

External fluid leakage 

• Loose connection between valve and pipe. Tighten the connection to the torque recommended by the small check valve manufacturer. 
• Worn-out rings. Replace the rings. 

Valve produces vibrations 

• Excess fluid flow velocity. Ensure the valve is working to the fluid velocity recommended by the small check valve manufacturer. 

No fluid flow through the small check valve 

• The valve is installed in the wrong direction. Verify the flow direction matches the flow arrow indicated on the valve body by the small check valve manufacturer or the one shown on the user manual guide. 
• Pipe blocked. Check the pipe delivering fluid to the small check valve for blockage and remove any such material leading to blockage. 
• Low suction pressure. Ensure the level of inlet pressure is as recommended by the small check valve manufacturer. 

Summary 

The small check valve is a small-sized valve used to prevent reverse fluid flow. Small check valves are used in low to medium-pressure applications. These valves depend on the pressure difference between the inlet and outlet of the valve to open and close the fluid flow. 

Small check valve manufacturers produce these valves with various materials for use in different applications. The type of material used to make the valve is the key factor to consider when purchasing the valve. The various applications of small check valves are freshwater supply, wastewater treatment, food applications, oil and gas, and chemicals among others.