Humphrey: Use Caution in Sizing Proportional Valves
In the pneumatic valve world, we often oversize valves for applications. Many times we size the valve strictly off of the port size that the customer wants to use, which can make the valve significantly higher in flow than is needed. This is not generally a problem in industrial applications as actuators can easily be slowed down using flow controls and the oversize situation will never be noticed.
While oversizing is not usually an issue with in on/off valves, correct sizing is necessary for proportional valves. Remember that a proportional valve allows the control of flow out of the valve based on the electrical input signal given. Oversizing of a proportional valve can cause loss of fine control in the output of the valve. For instance, if the valve is greatly oversized to the application, a signal to open 10% of the flow range of the valve will be a much greater flow than what may be needed. Therefore, opening the valve further will show no difference on the total system operation.
With a valve properly sized to the system requirements, the system will have the full range of adjustment that the valve will allow, making the system it is working in much more responsive and accurate. So, when specifying a proportional valve for a system, take the extra time to determine what is really needed and avoid the oversize dilemma.