Tuesday, December 6, 2016

Pressure Regulating Valves

industrial pressure regulator valve for steam brass
PIlot operated pressure regulator
intended for use in a steam system
Courtesy Pentair - Cash Valve
Many processes and equipment employ pressure regulating valves, the function of which is to maintain a desired outlet fluid pressure under varying conditions of supply pressure or outlet flow.

There are many pressure regulating valve variants, specifically designed to address a range of process conditions or offset a performance characteristic deemed undesirable in another design. Each variant has a suitable place in the range of possible applications, with cost, size, and complexity primary differences among the different offerings.

In its simplest form, a pressure regulating valve (PRV) consists of a flow restricting element, a measuring element, and a setpoint element. Outlet pressure applies force to the measuring element, often a diaphragm. As the outlet pressure increases, the diaphragm will move the flow restricting element toward the closed position, reducing the flow from the inlet. The restricting element is commonly a plug, disk, or some other recognizable valve trim arrangement. The setpoint element, likely a spring, provides a counterbalancing force on the diaphragm. When the force applied to the diaphragm by the outlet pressure reaches equilibrium with the counterbalancing force applied by the spring, movement of the restricting element stops. In this way, outlet pressure is controlled without the need for electric power, sensors, transmitters, or even a process controller. The entire assembly is self-contained and requires little attention.

Selecting a PRV for an application requires coordinated consideration of process performance range, desired conditions, and valve attributes to produce a selection that will provide the desired service. A valve improperly selected for an application may perform poorly. Some of the items to be considered include:
  • PRV Type
  • Body size
  • Construction
  • Pressure Ratings
  • Maximum Flow Rate
  • Outlet Pressure Range
  • Accuracy
  • Inlet Pressure
  • Orifice Diameter
  • Response Speed
  • Turn-Down Ratio
A PRV is not a safety device, so independent means must be provided to protect the system from excessive pressure. Product specialists are a good source of help in selecting a properly sized and configured valve for an application. Share your fluid process control challenges with a product application specialist, combining your process knowledge with their product application expertise to develop effective solutions.