EnglishWhy Is a Check Valve Installed at the Pump Outlet?
When a pump is operating normally, the fluid flows from the pump outlet into the downstream piping. After the pump stops, however, the fluid in the pipeline may not come to rest immediately. Due to residual pressure, static head from an elevated pipeline, or pressure differences within the system, the fluid may flow backward toward the pump.
A check valve is designed to open automatically during normal forward flow and close automatically when reverse flow begins, thereby preventing backflow.
For this reason, check valves are commonly installed on the discharge side of pumps. They help prevent reverse flow, reduce the impact of backflow on the pump, and protect the piping system and related equipment.
However, the role of a check valve goes beyond simply “preventing backflow.” The valve type, installation position, and closing characteristics can all affect the operating stability of a pumping system. Improper valve selection may lead to problems such as water hammer or pressure fluctuations.
What Happens When a Pump Stops?
When a pump stops, the flow conditions within the system can change.
In some systems, water may flow backward due to pressure in the pipeline, static head from an elevated section of piping, or other pumps that are still operating.
This commonly occurs in:
- Elevated pipeline systems
- Long-distance pipelines
- Booster systems
- Parallel pump systems
- Water supply systems with higher downstream pressure
Without a check valve, the reverse flow may enter the pump again and affect the normal operation of both the pump and the piping system.
Why Is a Check Valve Installed at the Pump Outlet?
A check valve is installed at the pump outlet mainly for three reasons: to prevent reverse flow, protect the pump, and help keep the system stable after the pump stops.
1 Prevent Reverse Flow
Preventing reverse flow is the most basic function of a check valve.
When the pump stops and the downstream fluid begins to flow back toward the pump, the check valve closes automatically to prevent the fluid from re-entering the pump.
This is especially important in water supply systems, pumping stations, booster systems, and pipelines with elevated sections.
2 Protect the Pump
If a large amount of fluid flows backward through a centrifugal pump, it may cause the impeller to rotate in reverse and increase the load on internal pump components.
In parallel pump systems, a check valve also prevents an operating pump from forcing fluid back through another pump that has already stopped.
For this reason, a check valve does more than prevent backflow. It also helps reduce the effects of reverse flow on the pump and related equipment.
3 Help Keep the System Stable
After a pump stops, the flow and pressure in the pipeline do not become stable immediately.
A properly selected check valve can limit reverse flow at the right time and help reduce the effects of sudden pressure changes.
However, a check valve is not the same as a dedicated water hammer protection valve. If its closing speed does not match the actual system conditions, it may still cause pressure fluctuations or even water hammer.
Therefore, selecting a check valve for a pump outlet should not be based only on valve size and pressure rating. Actual flow conditions, piping layout, and the valve’s closing characteristics should also be considered.
What Type of Check Valve Is Suitable for a Pump Outlet?
Several types of check valves can be used at a pump outlet, and no single type is suitable for every application. Selection usually depends on factors such as the fluid, pipe size, flow rate, available installation space, and the risk of water hammer in the system.
Swing Check Valve
Swing check valves have a simple design and a relatively open flow path. They are commonly used in water supply, drainage, and general industrial piping systems.
They are suitable for systems with relatively stable operating conditions. However, in pipelines where flow velocity changes quickly or where there is a higher risk of water hammer, special attention should be paid to the disc closing speed.
Dual Plate Check Valve
Dual plate check valves have a compact design and a short face-to-face dimension, making them especially suitable where installation space is limited.
They usually use spring-assisted closing, and the plates have a relatively short travel distance. For this reason, they are commonly used at pump outlets and in larger-diameter pipelines.
Silent Check Valve
Silent check valves are commonly used at pump outlets in clean water, HVAC, and booster systems.
They typically use spring-assisted closing. As the flow rate begins to decrease, the disc starts to close gradually, helping to reduce the amount of reverse flow before full closure.
Tilting Disc Check Valve
Tilting disc check valves are commonly used in larger-diameter pipelines and pumping station systems.
Compared with conventional swing check valves, they have a shorter disc travel and respond more quickly. Some models can also be equipped with counterweights or hydraulic damping devices to help control the closing process.
Ball Check Valve
Ball check valves are well suited for sewage, drainage, and fluids containing suspended solids.
Because of their relatively simple internal design, the flow path is less likely to be affected by debris or solids. For this reason, they are commonly used in sewage pumping stations and drainage systems.
In general:
- For ordinary clean water systems, Swing, Dual Plate, or Silent Check Valves can be considered.
- For large-diameter pumping stations, a Tilting Disc Check Valve may be suitable.
- For sewage or fluids containing suspended solids, a Ball Check Valve can be considered.
The final selection should still be based on the actual flow rate, pressure, fluid characteristics, and piping layout.
Where Should the Check Valve Be Installed?
In many pumping systems, the check valve is installed close to the pump outlet. A common arrangement is:
Pump → Check Valve → Isolation Valve → Pipeline
The check valve is used to automatically prevent reverse flow, while the isolation valve is used to shut off the pipeline during inspection or maintenance. The two valves serve different purposes and cannot replace each other.
Different types of check valves also have different installation requirements:
-
Swing Check Valve
Swing check valves are commonly installed in horizontal pipelines. Some models can also be installed in vertical pipelines with upward flow, but this should be confirmed based on the valve design and the manufacturer’s requirements. -
Dual Plate Check Valve
Dual plate check valves can be installed in horizontal pipelines and are also commonly used in vertical pipelines with upward flow. During installation, make sure the flow direction matches the arrow marked on the valve body. -
Silent Check Valve
Silent check valves are often installed at pump outlets and can generally be used in horizontal pipelines or vertical pipelines with upward flow. Because they use spring-assisted closing, they are usually more flexible in terms of installation orientation. -
Tilting Disc Check Valve
Tilting disc check valves are commonly used in horizontal pipelines and larger pumping systems. Some designs may also be suitable for other installation orientations, but this should be confirmed according to the specific valve construction. -
Ball Check Valve
Ball check valves are commonly used for sewage, drainage, and fluids containing suspended solids. Depending on the valve design, they can be installed in horizontal pipelines or vertical pipelines with upward flow.
Regardless of the type of check valve used, the installation direction must always match the direction of fluid flow, and the valve should be installed according to the product instructions or project design requirements.
The final installation position should also take into account the pump type, piping layout, available maintenance space, and actual system operating conditions.
The main purpose of installing a check valve at the pump outlet is to prevent reverse flow after the pump stops and to reduce the impact of backflow on the pump and piping system.
A properly selected check valve can help protect the pump, prevent backflow in parallel pump systems, and reduce the risk of pressure fluctuations or water hammer.
Union Valve supplies Swing Check Valves, Dual Plate Check Valves, Silent Check Valves, Tilting Disc Check Valves, and Ball Check Valves for a wide range of applications, including water supply, wastewater, HVAC, and pumping stations.
If you are selecting a check valve for a pump outlet, you can provide the valve size, pressure rating, fluid, flow rate, installation arrangement, and actual operating conditions. We can help you identify a more suitable valve type and configuration.
If you have any other questions, please feel free to contact us.
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