Compressed air systems require great amounts of energy, and to help reduce energy consumption, flow controllers have been developed. The typical flow controller is installed in the piping of a compressed air system between the compressors (which supply the pressurized air) and the point of use. The purpose of the flow controller is to maintain a desired or set point pressure downstream from the flow controller.
Without a flow controller, pressure in the piping varies with the loading and unloading of the compressor. Because of this variation, the compressor must work at higher levels in order to maintain minimum pressure levels throughout the system. With a flow controller, the downstream pressure is maintained at a constant level, thereby allowing the compressor to work less hard and consume less energy.
Flow controllers work by measuring downstream pressure using a transducer, and then adjusting the position of a valve to increase or decrease the pressure flow through the flow controller. In the past, flow controllers have used the air pressure in the system itself to actuate a positioner, which in turn drives the valve.
However, there are certain problems with such pneumatically actuated flow controllers. First, pneumatically-actuated positioners tend to fail because the pressurized air often carries with it moisture and contaminants, which interfere with the operation of the actuator. In certain cases, the moisture can even travel from the actuator through an electrical conduit down to the control panel, causing a short or other malfunction. Indeed, for compressed air systems that do not otherwise require a dryer, pneumatically-actuated positioners are unworkable, since the excess moisture will cause routine failure.
Second, these systems are prone to “hunting” or oscillation of the valve as its searches for the proper position to maintain set point pressure. “Hunting” results from a disparity between the relatively fast response time of the electronic means that are used to sample downstream pressure, and the relatively slow response time of the pneumatically-actuated positioner and valve.
Thus, there is a need for a flow controller that is not subject to failure resulting from contaminants in the pressurized air, and that is able to find and maintain the proper valve position without undue valve oscillation.