How to Select On-Off Valve Components- Zhejiang Lasen Intelligent Equipment Co., Ltd.

How to Select On-Off Valve Components

The on-off valve is a fluid equivalent of the electrical switch, it either allows unimpeded flow or acts to prevent it altogether. On/off valves are used for routing process fluid to different locations, starting or stopping batch processes, and engaging automated safety (shutdown) functions. Valve styles that are commonly used for on/off applications include ball, plug, butterfly (or disk), gate, and globe valves. These valves can be manually or actuated by the use of actuators.

The operating characteristics of on/off valves are quite simple: open when the handle is turned clockwise and closed when the handle is rotated counterclockwise. They are designed to provide a tight shut-off and should not leak when they are closed. Most business areas require on/off valves for ongoing operations and isolation of equipment or systems.

To ensure the on/off valve is positioned properly and operates correctly, it is often required to be installed with other components such as feedback limit switches and position transmitters. This helps to provide accurate positioning and avoid misoperation or damage of the valve. It is also possible to use electric actuators, which are more energy efficient and allow for easy positioning of the valve without needing to engage gears or other mechanical movements.

One of the most important things to consider when selecting a valve for on/off service is the nature and properties of the fluid being controlled. For example, the temperature, corrosiveness, and viscosity of the fluid may impact the choice of valve material and type. Other considerations include the valve's operating conditions, such as pressure and temperature, which will have an impact on the durability of the valve.

Another key factor is the application/service that the on/off valves are to be used in. For example, it is a common practice for engineering companies to select piping valves that are designed for on/off service as control valves in throttling applications. This is done as it is cheaper, already in the piping specification, and may have less leakage than a valve that has been specially sized for control purposes. However, this can result in problems when the valve is opened and closed.

When selecting an on/off valve for a specific application, it is recommended that the engineer use on/off valves that are specified for isolation duties and meet the required leakage specifications. It is also recommended that a higher inherent flow characteristic be specified for the valve, such as v-notch ball or toothed butterfly valve. This will help to achieve a better-installed characteristic that meets the throttle requirements of the application. It is also advised that engineers should specify a % deadband and a % stick-slip (resolution or threshold sensitivity) for the valve, which will help to ensure that the valve can be set up with a tight shut-off leakage class when needed.