When it comes to choosing a valve for flow control, there are so many factors involved. However, valve selection and sizing might be a very complicated process, but an engineer can start the process by understanding the requirements and finding the suitable valve to meet their needs. So in this article, we will look at the process of selecting a valve for flow control.
The type of valve you will get depends on the flow control, value operations and functions. For flow control, you need to select a KP-LOK valve type with goof throttling performance. The valve’s size needs to be selected to provide flow control over the range of opening of the valve plug.
Valves with characterized plugs can be chosen to alter the flow of the valve. Plug and ball valves are not the best choices for flow control.
If you want to prevent back-flow, then you should select a check valve. Applications that require pressure control would need a pressure regulator or pressure regulating valve.
The media flowing through the system can impact on valve selection. Applications with granules, powders, and other bulk materials are necessary for solid valves. The media flowing through the valve will define the category of valves such as steam valves, water valves, gas valves, hydraulic valves, vacuum valves, solid valves or air valves.
Another process of selecting a valve is called valve sizing. The selection of the proper valve size is essential in valve selection (in fact it is the most crucial step in valve selection).
A valve that is not correctly sized for an operation can cause operating problems within the valve or probably elsewhere in the fluid transfer system. For instance, an undersized valve can choose flow downstream and also create upstream back pressure. And an oversized valve can only regulate flow over a limited range near the closed position.
Apart from the performance problems, a valve that is not sized correctly will add unnecessary cost additions to your project.
If your application requires a block or isolating valve, on/off, or a check valve, then the valve can be sized to the existing pipe, hose or tube sizes. Ideally, in the open condition, flow should proceed in a way like there is no valve in line. The sizing of the valve is very crucial because of the flow constriction changes with the changing gap between the plug and seat.
The flow valve coefficient (CV) is used to calculate the proper valve size while maintaining a stable flow. The equation to calculate the valve flow coefficient (CV) is:
CV= Flow x m (specific gravity of the media at flowing temp/pressure drop) ½
One typical mistake engineers make when calculating the flow rate coefficient (CV) is calculating it too high by using the maximum flow rate. That results in the selection of an oversized valve. The range of flow (minimum, maximum, and mean flow rate) should be utilized to fit the valve correctly.
Valve actuation, connections, and certification
How the valve will be operated within your plant is another process in valve selection. If your valve is manually operated, then you need a manual valve with a handle or hand wheel for opening and closing the valve.
If the valve is to be installed in an aircraft, chemical plant, or vehicle where the valve must be able to turn off and on automatically, then you will need a hydraulic, electric, or pneumatic actuator to turn or slide the stem based in control signal inputs.
You also have to consider the valve end connection. The valve end connection is defined by the existing links in the piping system. If the existing chemical plant has flanged fittings, the valves with flanged ends must be located.