Skip to main content

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

Popular posts from this blog

The Intuitive Lowest Cost Method

The Intuitive Lowest Cost Method Or The Minimum Cell Cost Method

The Intuitive Lowest Cost Method is a cost based approach to finding an initial solution to a transportation problem.
It makes allocations starting with the lowest shipping costs and moving in ascending order to satisfy the demands and supplies of all sources and destinations.

This straightforward approach uses the following steps.
Identify the cell with the lowest cost.Allocate as many units as possible to that cell without exceeding the supply or demand.Then cross out the row or column or both that is exhausted by the above assignment.Move on to the next lowest cost cell and allocate the remaining units.Repeat the above steps as long as all the demands and supplies are not satisfied. 
When we use the Intuitive Approach to the Bengal Plumbing problem, we obtain the solution as below.

Transportation Matrix for Bengal Plumbing From \ To Warehouse E Warehouse F Warehouse G Factory Capacity Plant A Rs.50
Rs.40 100 Rs.30 100 Plant…

Vogel's Approximation Method (VAM)

The Vogel's Approximation Method

In addition to the North West Corner and Intuitive Lowest Cost Methods for setting an initial solution to transportation problems, we can use another important technique - Vogel's Approximation Method (VAM).
Though VAM is not quite as simple as Northwest Corner approach, but it facilitates a very good initial solution, one that is often the optimal solution.
Vogel's Approximation Method tackles the problem of finding a good initial solution by taking into account the costs associated with each alternative route, which is something that Northwest Corner Rule did not do.

To apply VAM, we must first compute for each row and column the penalty faced if the second best route is selected instead of the least cost route.

To illustrate the same, we will look at the Bengal Plumbing transportation problem.

Transportation Matrix for Bengal Plumbing From \ To Warehouse E Warehouse F Warehouse G Factory Capacity Plant A
Rs.30 100 Plant B


Oligosony is a Market Form in which the number of buyers is small while number of sellers in theory could be large. This typically happens in a market where numerous suppliers are competing to sell their product to a small number of (often large & powerful) buyers. This allows buyers to exert a great deal of control over the sellers and can effectively drive down prices. An Oligopsony is a form of imperfect competition. It contrasts with Oligopoly, where there are many buyers but few sellers. However, Oligopsony tends to be just as prevalent in the real world. In fact, the firms operating as Oligopoly in an output market, also often operate as Oligopsony in an input market. Most of the standard analysis that applies to the Oligopoly also applies to the Oligopsony. When a small number of relatively large buyers dominate an industry , they tend to dominate most facets of the industry. The reason that the term Oligopsony is seldom used is that term Oligopoly usually covers the entir…