By allowing media to flow through them only in one direction, non-return valves start working. These valves consist of two openings in the body, among which one is for the media to enter and the other is for the media to leave. Non-return valves work automatically, which means that most of them are not controlled by a person or an external control so they do not have a valve handle or stem.
Types of non-return valves
Ball Non-Return ValvesBall Non Return Valves have a closing member, the movable part to block the flow, which is a spherical ball. This is often spring-loaded to help to keep it shut. Apart from this, reverse flow is required to move the ball toward the seat and create a seat. The main seat of ball non-return valves is conically-tapered to guide the ball into the seat and form a positive seal when stopping reverse flow. These valves are small, simple and cheap.
Diaphragm Non-Return ValvesThese types of valves use a flexing rubber diaphragm to create a normally-closed valve. Pressure on the upstream side must be greater than the pressure on the downstream side for the valve to open and allow flow. Once positive pressure stops, the diaphragm automatically flexes back into its original closed position.
Swing Check Non-Return ValvesThis range of valves are characterized by a movable part to block the flow, which swings on a hinge or trunnion on to the seat to block reverse flow or off the seat to allow forward flow. The seat opening cross-section may be perpendicular to the centreline between the two ports or at an angle. Though Swing Check Non-Return Valve can have various sizes, the larger Non Return Valves are often swing check valves. Stop Check Non-Return Valves Stop Check Non-Return Valves come with override control to stop flow regardless of flow direction or pressure. It can be deliberately shut by an external mechanism as well as closing in response to insufficient forward pressure or backflow. Any flow regardless of forwarding pressure can be prevented by this.
Lift Check Non-Return ValvesThey come with a feature disc, which is also known as a lift and can be lifted up off its seat by higher pressure of inlet or upstream fluid to allow flow to the outlet or downstream side. When the pressure drops, gravity or higher downstream pressure causes the disc to lower onto its seat, shutting the valve to stop reverse flow.