Thursday, February 22, 2018

Pressure Regulating Valves

pressure regulating valve
Pressure regulating valve, or pressure regulator.
One of many types.
Image courtesy Cash Valve
Pressure regulating valves (PRV) are common components of many processes and equipment. The function of a PRV is to maintain a desired outlet fluid pressure under varying conditions of supply pressure or outlet flow demand.

Many variants exist in the market, each specifically designed to address a range of process conditions or offset a performance characteristic deemed undesirable in another design. Each has a suitable place in the range of possible applications, with cost, size, construction material and complexity primary differences among the 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. An 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. Leverage your own process knowledge and experience with their product application expertise to develop an effective solution.