The check valve is designed to pass the flow in one direction with minimum resistance and to avoid reverse or reverse flow with minimal leakage. The key types of check valve used are the swing check valve, the dual plate check valve, and the non-slam check valve.
A simple check valve contains a valve body, bonnet or cover, and a disc that is connected to a hinge and swings away from the seat of the valve to allow fluid to flow in the forward direction, as in a check valve for swinging or tilting discs and returns to the seat of the valve when the upstream flow is stopped. Therefore, reverse flow is stopped. The main advantage is that they are self-actuated and do not need any external means, either to open or close the valve to operate.
Types, function, and uses of check valves are:
Swing check valve: Due to the easy construction, low-pressure drop through the valve, and field serviceability, swing check valves are generally recommended for water and wastewater system applications.
Swing check valves are used for wastewater or services where dirt or other particles may be present in the fluid and positive shut-down is required, resilient seated swing check valves are typically recommended.
Generally, valve operation depends on gravity (weight of disc) and reversed flow. The pivot point of the swing check is outside the circumference of the disc and, the greater the flow velocity and head pressure probability the greater the valve closing force. The external hinge arm is available with either a lever weight or an adjustable spring to stop the slamming of the disc and eliminate hydraulic shocks.
Dual plate check valve: Compared to a traditional check valve, the dual plate check valve is an all-purpose non-return valve that is much tougher, lighter in weight, and smaller in size.
The concept of the Dual Plate Check Valve is the outcome of attempts to overcome the swing check valve and lift check valve problems. Two spring-loaded plates hinged on a central hinge pin are used by the Dual Plate Check Valve. As the flow decreases, the plates close without requiring reverse flow by torsion spring action. The twin benefits of no Water Hammer and Non-Slam simultaneously are provided by this design. All the characteristics make this valve one of the most successful designs. It is also the most versatile check valve that can be used for almost all the fluid applications.
Non-slam check valve: Non slam check valve is specifically intended to be used where there is a water hammer. These valves close without slamming, as their name implies. There is an innerspring opposing the disc of a non-slam check valve opening pressure for fluid flow. The spring compresses and the valve opens when the media flow is high enough; the disc is smoothly forced back by the spring to the seating surface in the valve as the flow reduces and slows, but before the flow path reverses.
