Friday, October 16, 2015

Check Valve

A Check Valve, Non Return Valve or a One way Valve is a valve that normally allows fluid (Liquid or Gas) to flow through only one direction.


Check Valves are two port valves, meaning they have two openings in the body, one for fluid to enter and the other for fluid to leave.
Check Valves work automatically and most are not controlled by a person or any external control, accordingly, they do not have any valve handle or stem.  

Check Valve Symbol on P&IDs. The Arrow shows the flow direction.

Check Valves are automatic valves that open with forward flow and close with reverse flow. The pressure of the flow passing through the system opens the valve, while reversal of flow will close the valve.



Types of Check Valves


Swing Check Valve

A basic Swing Check Valve consists of  a Body, a Bonnet and a disc that is connected to a hinge. The disc swings away from the valve seat to allow flow in forward direction, and returns to the valve seat, when upstream flow is stopped, to prevent backflow.

The disc in a swing check valve is unguided as it fully opens or closes. There are many discs and designs available, in order to meet the requirements of different applications.

Swing Check Valve
The Valves allow full, unobstructed flow and automatically closes as pressure decreases. These Valves are fully closed when the flow reaches to zero, in order to prevent backflow. Turbulence and pressure drop in the valve are very low.


Lift / Spring Check Valve

The seat and design of a Lift Check Valve is similar to a Globe Valve. The disc is usually is usually in the form of a piston or a ball, but without a hand wheel or any parts related to manual operation.

Lift Check Valves are particularly suitable for high pressure service where velocity of the flow is high. In Lift Check Valves, the Disc is precisely guided and fits perfectly into the Seat.



Lift Check Valve
Flow to Lift Check Valve must always enter below the seat. As the flow enters, the piston or the ball is raised within guides from the seat by the pressure of the upward flow.
When the flow stops or reverses, the piston or the ball is forced into the seat of the valve by both the backflow and gravity.


Wafer Type Single Plate Check Valve

Wafer type Check Valves have short face to face dimensions and low weight. They allow a simple space saving installation between two companion flanges.
The valves are suitable for mounting between two weld neck or slip on type companion flanges of different standards.



















They are specially developed for applications where a low pressure loss is essential. opening and closing of the valve will take place in an extremely low pressure difference over the valve disc. The eccentric disc shaft combination with the disc seat guarantees a positive shut off returning media. Wafer Check valves are becoming preferred types of check valves for most applications, due to their compact design and low cost. 


Wafer Type Single Plate Spring Check Valve

This Wafer type Check Valve consists of four main components, the body, a disc, a star guide and a spring. The disc check valves are opened by the pressure of fluid and closed by the compression spring as soon as the flow stops, thus preventing reverse flow.


 













The design of the these valves, Sandwich Type Single Disc Spring Loaded Check Valves allows them to be installed between any flanges of different standard in any position, including vertical pipelines where the fluid flows downwards.


Wafer Type Dual Plate Check Valve

Dual Plate Wafer Check Valve employs two springs loaded plates hinged on a hinge pin. When the flow decreases, the plates close by the action of torsion spring before the flow reversal takes place.














All features put together make the Dual Plate Check Valve as the most efficient and versatile design. It is also referred to as Silent Check Valve. It is much easier to install between standard gaskets and line flanges, and therefore it is more cost effective to install and to maintain.
It is also called Butterfly Check Valve.   


Sinking Ball Check Valve




Recoil Check Valve