A Little Lesson on Why To Choose The Correct Valve Size
The flow coefficient of a valve or CV, dictates the valve’s performance and much more than just how much flow can pass through the valve. A correctly sized valve will operate quieter, offer more accurate flow control, will last longer and will not leak. The CV calculation is crucial as it affects all of these things.
If a valve is too small for a given application you won't get enough flow through the valve. An undersized valve will mean the system has to compensate by raising the head pressure of the pump and will give a much higher differential pressure across your valve. When your media leaves the valve a sudden drop in pressure causes it to flash and bubble, otherwise known as cavitation which can considerably reduce the life of the valve. The flashing of liquid creates vibration and turbulence in the line which will wear out the seats and seals. It can cause weak joints in the piping to leak; and the sound of the vibration can carry throughout your system.
With an oversized valve there is a less likely chance of damage to the system but controllability becomes an issue. If the valve is heavily oversized and you are using a modulating control valve it may need much more significant position changes to achieve the required flow change. This could cause your valve to hunt and overshoot constantly, which will wear out the valve and the actuator prematurely.
To help you out with all your valve sizing needs we've added the Jordan Valve JVCV valve sizing software to the Engineered Solutions & Services section of our website! This is available online or if you prefer there is a downloadable version too.