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.
Proportional valves respond to variations in current applied to the solenoid by delivering a corresponding variable flow output. They are becoming a popular choice for machine and device builders desiring more flexibility in flow or pressure output from a PLC based on the conditions of the machine or making the machine "more flexible for the customers automation needs.”