A check valve is one of those elements of a piping system that is often forgotten during design, but remembered after an accident. Without it, a pump can run idle, a boiler can be damaged by water hammer, and a sewer can flood a basement.
The range will help you choose the right type of valve for your system. check valves from UKSPAR.
What is a check valve and why is it needed?
A check valve is an automatic shut-off device that allows medium to pass in only one direction and automatically closes when the flow direction changes or pressure drops.
Unlike gate valves and ball valves, which are controlled by an operator, a check valve operates independently.
How a check valve works in a piping system
The basis of operation is the pressure difference. When the pressure at the inlet (from the side of the medium flow) exceeds the pressure at the outlet, the shut-off element opens and allows the flow. As soon as the pressure equalizes or a reverse flow occurs, the element closes under the action of a spring, the mass of the disc itself, or the reverse flow itself.
Structurally, the check valve consists of:
- housing - usually cast iron, steel, bronze, brass or stainless steel;
- a locking element - a disk, ball or plate;
- saddles - the seating place of the locking element;
- springs (in spring models) - ensures reliable closure without backflow.
Why is a backflow preventer needed?
Backflow in a pipeline can cause:
- water hammer - a sharp jump in pressure when the pump stops, which can damage the pipeline, equipment and connections;
- pump damage - the turbine rotates in the opposite direction, which destroys the bearings and impeller;
- drinking water contamination - backflow from a tank or boiler can introduce bacteria or iron into fresh water;
- basement flooding - due to backflow in the sewer;
- reduced system efficiency - pumps or boiler do not accumulate pressure because it "drains" back through an unprotected pipeline.
The principle of operation of a check valve
A check valve operates automatically and allows fluid to flow in one direction only. Its primary function is to prevent backflow, which can damage equipment, disrupt system operation, or cause water hammer.
How the locking element opens and closes
In a spring-loaded valve, the closing element (disc or ball) is held closed by a spring. When the inlet pressure exceeds the spring force plus the outlet pressure, the element moves back and opens the passage. When the inlet pressure drops, the spring returns the element to its original position, closing the valve.
In a rotary valve, the closing element (disc) is suspended on a hinge. The flow lifts the disc and opens the passage.
Valve operation when pressure changes in the system
The closing time of the valve is crucial. If the valve closes slowly, the reverse flow has time to gather speed, and a sudden closure causes water hammer. Spring-loaded valves close faster - the spring pressure is independent of the flow rate. Rotary valves close more slowly and can cause water hammer in large pipelines.
For pumping stations with large diameters and significant flow rates, valves with a shock absorber or hydraulic damper are used, which slows down the closing of the disc in the final stage and prevents impact.
Main types of check valves
Check valves differ in the design of the closing element, the method of operation, and the conditions of use in the pipeline system.
Ball check valves
In a ball check valve, a metal or rubber ball serves as the closing element. Flow raises the ball and opens the passage; when the flow stops, the ball drops onto the conical seat and closes the passage.
- Advantages: simple design, high reliability, low hydraulic load.
- Disadvantages: limited application diameters (usually DN 15–50), correct orientation during installation is required.
- Application: water supply systems, domestic pumping stations, boiler connection systems.
Turnstiles and their features
The rotary check valve is one of the most common types for large DNs. The disc is suspended on a hinge at the top of the body and rotates freely depending on the flow direction.
- Advantages: low hydraulic resistance in the open position, suitable for large diameters, simple design.
- Disadvantages: possible water hammer during quick closing, requires horizontal or somewhat inclined installation.
- Application: main water pipes, pumping stations, heating stations, industrial pipelines DN 50–800.
Flanged check valves
A flanged check valve is a compact device without its own flanges that is clamped between two pipeline flanges. It is usually made in the form of a double-leaf or single-disc spring valve.
- Advantages: very compact, lightweight, cheaper than flanged counterparts for large DN, lower hydraulic resistance due to double-leaf design.
- Disadvantages: cannot be installed without pipeline flanges; dismantling requires disassembly of the flange connection.
- Application: pumping stations, cooling systems, industrial pipelines DN 50–600.
Classification of check valves by installation method
| Connection type | Description | DN range |
| Carved | Threaded mounting, quick installation | DN 15–80 |
| Flanged | Bolted connection, removable | DN 50–800 |
| Welded | Non-separable, maximum tightness | DN 50–600 |
| Inter-flange | Without own flanges, clamp between pipeline | DN 50–600 |
In addition to the connection method, the mounting orientation is important. Most spring-loaded valves can be mounted horizontally or vertically (flow from bottom to top). Rotary valves are mounted only horizontally or at an angle - vertical mounting with flow from bottom will result in improper disc closure.
The check valve body must have an arrow indicating the direction of flow. Mounting "against the arrow" completely blocks the flow.
Where are check valves used?
A water check valve is installed at the pump outlet of the pumping station to prevent water from flowing back from the pressure pipeline when the pump stops. It is also installed at the cold water inlet to the boiler to protect against water hammer and backflow from the boiler.
A check valve on the boiler is a mandatory connection element. It protects the cold water supply network from hot water from the boiler during pressure surges.
A non-return valve for heating is installed on the circulation pump. It prevents the coolant from circulating when only one of the pumps installed in parallel is operating.
A sewer check valve is installed on the sewer branch from the house. When the level in the city sewer network rises (for example, during a downpour), the valve automatically closes and prevents flooding of the basement or bathrooms.
A check valve for a pumping station is one of the key protection elements. It is installed at the outlet of each pump during parallel operation so that the stopped pump does not receive reverse flow from the operating ones.
Key parameters for selecting a check valve
When selecting a check valve, you need to consider the system characteristics, flow direction, type of working medium, and installation conditions.
Valve selection by operating pressure
The nominal pressure PN of the check valve must be equal to or greater than the maximum pressure in the system. For domestic systems, PN 10–16 is usually sufficient. For industrial pipelines, PN 25–40 and higher.
It is also important to consider the opening pressure - the minimum pressure drop at which the valve starts to open. For spring-loaded valves, it is 0.1–0.5 bar.
Selection of housing material and connection type
Brass - for domestic water supply systems DN 15–50, cold and hot water.
Ductile iron (GGG-40) — for DN 50–300 systems, water supply and heating.
Stainless steel - for the food industry, aggressive environments and elevated temperatures.
PVC or PVDF - for chemical lines with acids, alkalis, chlorine.
Sealing (seat and disc material):
- EPDM — water, steam up to 130 °C, ozone;
- NBR - petroleum products, lubricants;
- PTFE (Teflon) — chemical environments, high corrosion resistance;
- Stainless steel - high temperature (over 150 °C), par.
How to choose diameter and throughput
The DN of the check valve must match the DN of the pipeline. Underestimating the DN increases hydraulic resistance and can cause cavitation; overestimating it will lead to unstable operation at low flow rates (the disc will not open completely and will vibrate).
Advantages and disadvantages of different types of check valves
| Type | Advantages | Disadvantages |
| Spring (disc) | Quick closing, any orientation | Higher hydraulic resistance |
| Swing | Low hydraulic resistance | Water hammer possible, only horizontal |
| Ball | Simplicity, compactness | Small DN, limited orientation |
| Interflange double-leaf | Compact, low resistance | Complex dismantling |
| Lift check | High tightness | Horizontal only, higher resistance |
Typical mistakes when selecting and installing a check valve
Wrong choice of valve type. A rotary valve in a pumping station with frequent starts and stops is a risk of water hammer. A spring-loaded or interflange double-leaf valve is better suited for such conditions.
Installation errors in the direction of flow. The most common error is installation "against the arrow". The valve completely blocks the flow and does not open. Before installation, be sure to determine the direction of flow in the pipeline.
Mounting the rotary valve in a vertical position. A rotary valve mounted vertically with flow downwards will not close under the weight of the disc. Be sure to check the product data sheet for the permissible orientation.
Valve mismatch with the operating environment. A standard brass water valve installed on a system with chlorinated or acidic water will quickly fail due to corrosion. Select materials according to the chemical composition of the environment.
Ignoring the opening pressure. In systems with low operating pressure (gravity heating, gravity systems), a spring-loaded valve with too high an opening pressure will be permanently closed, which will disrupt circulation. Choose valves with a minimum opening pressure or springless designs.
Conclusion
A check valve is a small but critically important element of piping system protection. A properly selected and properly installed valve protects pumps, boilers, and networks from water hammer and backflow, extending the service life of all equipment.
