Check valve are installed in pipelines to allow flow in one direction only. Check valve are also called non return valve. It is operated entirely by reaction to the line fluid and therefore do not require any external actuation. Types including lift, disc, swing and wafer check valves.
What is check valve function
A check valve is allows fluid to flow in one direction only. It is also known as a one-way valve or non-return valve. Check valves are used in various of applications, including:
- Preventing backflow: This is the most common function of a check valve. Backflow occurs when fluid flows in the opposite direction of intended flow. This can damage equipment, contaminate fluids, and create safety hazards. Check valves prevent backflow by closing when the fluid flow reverses.
- Protecting pumps: Check valves can be used to protect pumps from damage caused by backflow. When a pump is turned off, the fluid in the pump’s suction line can flow back into the pump. This can damage the pump’s impeller and bearings. A check valve installed on the pump’s discharge line prevents this backflow from occurring.
- Maintaining system pressure: Check valves can be used to maintain system pressure by preventing fluid from flowing back into a tank or reservoir. This can be helpful in applications where the fluid is under pressure, such as water supply systems and fire sprinkler systems.
- Isolating systems: Check valves can be used to isolate systems from each other. This can be helpful in maintenance and repair applications, as well as in emergency situations.
Functional parts of a check valve
Valve Body :The valve body is the housing for the check valve. It is typically made of metal or plastic.
Disk or Ball :The disk or ball is the part of the check valve that closes to prevent fluid flow in the opposite direction. It is typically made of metal or rubber.
Spring: The spring is used to keep the disk or ball in the open position when there is no fluid flow.
Gasket: The gasket is used to seal the valve body and prevent fluid leakage.
Types of Check valves
Piston Lift check valves
The piston lift check valve is a modification of the standard lift check valve. It incorporates a piston shaped plug instead of the cone, and a dashpot is applied to this mechanism. The dashpot produces a damping effect during operation, thereby eliminating the damage caused by the frequent operation of the valve, for example, in pipeline systems, which are subject to
surges in pressure, or frequent changes in flow direction.
The main advantage of the lift check valve lies in its simplicity, and as the cone is the only moving part; the valve is robust and requires little maintenance. In addition, the use of a metal seat limits the amount of seat wear. The lift check valve has two major limitations; firstly, it is designed only for installation in horizontal pipelines, and secondly, its size is typically limited to 3”, above which, the valve would become too bulky.
A swing check valve consists of a flap or disc of the same diameter as the pipe bore, which hangs down in the flow path. With flow in the forwards direction, the pressure of the fluid forces the disc to hinge upwards, allowing flow through the valve. Reverse flow will cause the disc to shut against the seat and stop the fluid going back down the pipe.
In the absence of flow, the weight of the flap is responsible for the closure of the valve; however, in some cases, closure may be assisted using a weighted lever. As can be seen from below picture the whole mechanism is enclosed within a body, which allows the flap to retract out of the flow path.
Swing check valve produce relatively high resistance to flow in the open position, due to the weight of the disc. In addition, they create turbulence, because the flap ‘floats’ on the fluid stream. This means that there is typically a larger pressure drop across a swing check valve than across other types.
Both lift and swing check valves tend to be bulky which limits their size and makes them costly. To overcome this, wafer check valve have been developed. By definition wafer check valve are those that are designed to fit between a set of flanges. This broad definition covers a variety of different designs, including disc check valves and wafer versions of swing or split disc check valves.
Disc check valves
The disc check valve consists of four main components: the body, a disc, a spring and a spring retainer. The disc moves in a plane at right angles to the flow of the fluid, resisted by the spring that is held in place by the retainer. The body is designed to act as an integral centering collar that facilitates installation. Where a ‘zero leakage’ seal is required, a soft seat can be included.
When the force exerted on the disc by the upstream pressure is greater than the force exerted by the spring, the weight of the disc and any downstream pressure, the disc is forced to lift off its seat, allowing flow through the valve. When the differential pressure across the valve is reduced, the spring forces the disc back onto its seat, closing the valve just before reverse flow occurs. This is shown in Figure above The presence of the spring enables the disc check valve to be installed in any direction.
Where to install check valve before or after pump
A check valve is often fitted after a pump to avoid backflow. When the pump is turned on, it creates a pressure difference between the intake and exit sides of the pump. This pressure difference can cause fluid to flow back into the pump if there is no check valve in place. This can damage the pump and even cause it to fail.
A check valve can also be installed before a pump, but this is not as common. A check valve installed before a pump can assist prevent the pump from running dry. This is because when the pump is switched off, the check valve will stop fluid from flowing back out of the pump. However, installing a check valve before a pump can also restrict flow, which can reduce the efficiency of the pump.
In general, it is best to install a check valve after a pump to prevent backflow. However, there may be some cases where it is necessary to install a check valve before a pump to prevent the pump from running dry.
Examples of where a check valve might be installed before or after a pump
In a water well system, a check valve is typically installed after the pump to prevent backflow. This is important because the water in the well is usually under pressure, and if the pump fails, the water could flow back into the well and contaminate it.
In a fire sprinkler system, a check valve is typically installed before the pump to prevent the pump from running dry. This is important because the fire sprinkler system needs to be able to deliver water quickly in the event of a fire, and if the pump runs dry, the system will not be able to function properly.
In a sump pump system, a check valve is typically installed after the pump to prevent backflow. This is important because the sump pump is used to remove water from a basement, and if the pump fails, the water could flow back into the basement and cause flooding.
where to install check valve on water pump
A check valve can be installed on a water pump in a few different places, depending on the specific application.
In the suction line: A check valve can be installed in the suction line of the pump, just before the pump itself. This will help to prevent backflow from damaging the pump.
In the discharge line: A check valve can also be installed in the discharge line of the pump, just after the pump. This will help to prevent cavitation and protect the pump from damage.
In the bypass line: A check valve can be installed in the bypass line of the pump, which is a separate line that bypasses the pump. This can be useful if the pump fails or needs to be serviced.
The best place to install a check valve on a water pump will vary depending on the specific application. It is important to consult with a qualified plumber or engineer to determine the best location for the check valve.
Considerations when installing a check valve on a water pump
The size of the check valve: The check valve should be the same size as the pipe that it is installed in.
The type of check valve: There are different types of check valves available, such as swing check valves, ball check valves, and spring check valves. The type of check valve that is best for a particular application will depend on the specific needs of the system.
The installation method: The check valve should be installed in accordance with the manufacturer’s instructions.
Maintenance: The check valve should be inspected regularly for signs of wear or damage. If the check valve is damaged, it should be replaced immediately.
Check Valve Installation position
The check valve installation position is important to ensure that it functions properly. The flow arrow on the check valve should be positioned so that it points in the direction of the desired flow. This ensures that the valve opens to permit fluid flow in the desired direction and closes to prohibit fluid flow in the opposite direction.
In general, check valves can be installed in either a horizontal or vertical position. However, there are some specific considerations for each type of installation.
Horizontal installation: When installing a check valve in a horizontal pipe, the valve should be installed so that the flow arrow is pointing in the direction of the desired flow. The valve should also be installed with a slight upward tilt, so that the valve disc is not resting on the valve seat. This will help to prevent the valve from sticking or becoming damaged.
Vertical installation: When installing a check valve in a vertical pipe, the valve should be installed so that the flow arrow is pointing upwards. The valve should also be installed with a support bracket, so that the valve does not sag and become damaged.
Advantages of check valve
Prevents backflow. As mentioned above, check valves are very effective at preventing backflow. This can protect equipment, prevent contamination, and even save lives.
Protects pumps. Check valves can protect pumps from damage caused by backflow. This can save money on repairs and downtime.
Maintains flow. Check valves can maintain flow in a system even if there are changes in pressure or direction. This can be important in applications where a constant flow is required.
Isolates systems. Check valves can isolate different parts of a system from each other. it can be useful for maintenance or repair purposes.
Disadvantages check valve
Can restrict flow: Check valves can restrict flow, especially if they are not properly sized. This can reduce the efficiency of a system.
Can be noisy: Some types of check valves can be noisy, especially when they are opening and closing frequently.
Can be prone to clogging: Check valves that are used with dirty or contaminated fluids can be prone to clogging. This can reduce the flow of fluid and even cause the valve to fail.