Types of Valves and Their Applications
The following will help you to understand the proper use and the terminology relative to the type of valve to be used in given applications.
Gate valves are found primarily on water distribution lines and are designed only to start or stop flow. Activation of the valve is done by turning a hand wheel or by turning the operating nut with a valve key. The valve wedge is attached to the valve stem, which is activated by the hand wheel or operating nut. Opening the valve pulls the wedge up into the bonnet and out of the flow, while closing pushes the wedge into the body of the valve, stopping the fluid. A gate valve should not be used for throttling for prolonged periods because vibration of the wedge will eventually wear and damage the valve. If throttling is desired, then the use of a butterfly valve should be considered.
Butterfly valves have a rotating disc that turns within the body of the valve. The disc is attached to a stem which, in turn, is connected to the valve’s actuator that, when operated, causes the disc to open or close with each quarter turn. Butterfly valves can completely stop the flow, let the fluid pass in the full open position, or regulate flow by having the disc turned at an angle to slow the passing of fluid, known as throttling. The disadvantage in the use of a butterfly valve is that the disc always remains in the path of the fluid, making effective cleaning of the lines difficult.
Check valves are designed to allow flow in only one direction. The most common use in a water system is on the discharge of pumps to prevent backflow when the pump shuts down. Check valves have a disc that is attached to a hinge so that when the flow is in the same direction as the opening of the disc, the valve is open. When pressure decreases in the direction of flow, the disc will close, preventing backflow or fluid from entering the valve from downstream. Check valves can be equipped with an outside lever and weight to assist with the closing process. A check valve with an outside lever and weight is more likely to be found in use with a sewer-related system.
Plug valves are defined as eccentric because of the manner in which the plug works. By turning the operating nut or actuator from the closed to open position (approx. 90 degrees), the plug turns, exposing a rectangular port which the effluent passes through. This valve can be used as a throttling device or as one with frequent on/off service and is useful in crushing trapped solids.
Understanding the terms, names and functions of the different types of valves will allow for more constructive discussion about the valves to be used for the project and thereby make decisions more efficient.