Check valves prevent backflow in a piping system. Also known as non-return valves or NRV, these mechanisms ensure that the valve closes if the fluid flow passing through the pipe reverses. Ensuring unobstructed flow, a check valve can automatically close when pressure decreases. They are found in many industries with applications in mining, natural gas, and water. Check valve purchases typically take into consideration line size, pressure class, working pressure, flow rate, and media gravity and temperature.
The Ball Check Valve replaces the disk device often used to prevent flow with a ball that relies on gravity. Under pressure from the flow, the ball will lift up out of the pipe outlet. When low pressure lessens sufficiently, the ball falls back into place to stop the flow. The ball check valve is a type of lift valve.
Also known as a butterfly valve, the double door or dual plate check valve features a disc divided in two along a centre line. The two doors can hinge open to allow forward flow or arrest backflow. Compact and lightweight, this type of check valve is often implemented for low-pressure liquid and gas applications.
This type of valve is typical in applications requiring high-pressure service. Effective with a high-velocity flow, lift check valves can be installed either horizontally or vertically (in pipelines with an upward flow). Types of lift check valve include piston type and ball type. This type of valve can prove more leak resistant.
The piston check valve is a type of lift valve. The valve is opened or closed by the pressure (or lack of pressure) passing through the pipe. Gravity forces the piston valve’s weight into the closed position if the flow reverses itself.
Combining the advantages of lift check and globe valves, the stop check valve offers override control, regardless of flow direction. While some other types are dependent on gravity, the stop-check valve can be closed deliberately using an external mechanism. This provides flow control regardless of backflow or forward flow level. This type of valve helps prevent damage to equipment such as boilers or pumps.
A prevalent check valve with its disc completely out of the way when the material is flowing. The disc swings back into place over the pipe when not in use. This means swing check valves close slowly. These valves are common in applications with a high solids percentage and lower on/off cycle count.
A variation on the swing check valve, the tilting disc is spring-assisted to stay in the flow stream, with media flowing around it. Available in wafer or lug type design, this valve type has a disc which tilts up under steady pressure from the fluid flow. As the flow level lowers, the disc will revert to a closed position. The disc simply floats on the surface of the media when the forward flow is sufficient to overcome the spring tension.
Check valves are also characterized by their application. Examples of these include wastewater, oilfield, marine, or beverage. Suppliers also characterize check valves by the material used in the valve body, such as titanium, plastic, and rubber.