A pressure controller's sole function is to control the pressure of a pipeline. Engineers specify the pressures at which the fluid or gas should flow. Excessively low pressure leads to insufficient flow, and excessively high pressure creates the risk of a blowout. For gases, if the pressure is too great, the possibility exists that the gas will turn into a liquid. Pressure controllers have complex internal valving to limit the flow and in turn maintain the optimum pressure level. Pressure controllers are not just for pipelines. A continuously variable transmission (CVT), for example, uses hydraulic fluid and internal pipes, requiring a pressure controller to monitor the flow of the fluid. The pressure controller is called the ratio control valve.
The controller matches the size and flow rate of the pipe. Controllers for small-diameter pipes fit inside the palm of your hand, while controllers for large pipes are hauled in by a crane. The size and shape of the controller usually follows the size of the pipe and the required operating pressures.
Methods of control range from simply turning a handle to engaging complex computerized robotic valves. Computerized controllers are hooked up to a central computer, which reads the pressure in the pipe via specially located sensors and adjusts the controller to bring the pressure into specified limits. The program itself is written by a team of engineers and other professionals, who design and test the system.
A regulator is a type of controller, but a controller is not a regulator. A regulator's sole function is to take varying pressures at the input and produce a constant pressure at the output. University of Massachusetts engineer Dr. Yu-li Wang designed a regulator circuit for medical labs. The input gas can have unstable pressures, varying from 30 to 40 psi. The regulator produces a constant output of 15 psi. A controller, on the other hand, is used to control the pressure. It's completely adjustable, so the fluid or gas pressure inside the pipe is set to a certain level and maintained.