Travel at maximum flow should fall below 90 percent whereas travel for minimum flows should be above 20 percent open to avoid erosion of the trim. Some industry literature recommends travel at normal flow should fall within 50 to 70 percent opening angle. When a valve is sized correctly, the range of operation will correspond well to the control range of the valve. This item is discussed in a little more detail later. The flow characteristic can be generally thought of as the change in rate of flow in relationship to a change in valve position. Different valve types have different flow characteristics. Consider the inherent flow characteristic of the control valve you are selecting.Consider the degree of control you require and ensure the selected valve is mechanically capable of achieving the desired operating conditions.Consider the local ambient atmosphere and any corrosives that can occur which may affect the exterior of the valve.
Consider the operating temperature and pressure the control valve will be exposed to.Take into consideration the components of the valve that come in to contact with the process fluid such as the valve body, the valve seat or any other valve components exposed to the process fluid. Give careful consideration to selecting the correct materials of construction.The following list outlines some of the things to consider when making a control valve selection: Selecting an improperly sized control valve can have serious consequences on safety, operation and productivity.
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