In previous blogs, we’ve touched on the “Regulator Hierarchy”. As a review, the hierarchy is as follows:
Self-operated PRVs are the simplest type. Relatively low cost and relatively accurate regulation. Price and accuracy will vary by manufacturer.
Pilot-operated regulators use a pilot valve to amplify the signal to the main valve. Pilot-operated valves provide greater accuracy and higher turn-down ratios.
Dome-loaded valves combine the rugged simplicity of self-operated valves with the greater accuracy and turn-down ratios of a pilot-operated regulator.
Unlike other regulators, dome-loaded regulators do not have a spring; the spring force is replaced by an air (or other appropriate medium) signal loaded into the dome. The air signal determines the set point.
Dome-loaded regulators provide a closer degree of control than self-operated or pilot-operated valves, while providing greater flexibility. They are an excellent choice where great accuracy is required (minimize droop), remote control is needed, or where the set point changes frequently.
Benefits in Steam Applications
Typical problems associated with controlling steam flows have generated many theories on how to improve the control loop; many of which are sophisticated and expensive.
A simpler approach might yield greater results in both temperature control and cost efficiency. Remotely set dome-loaded PRVs enable the steam equipment to operate and respond more quickly to varying conditions. The regulator allows more flow to pass more quickly upon sensing a loss of pressure, thereby reducing fluctuations in output temperature.
The benefits of this application can be measured in dollars. Eliminating control valves, controllers, and other elements in the control loop represents a large cost savings. Reducing the complexity of the control loop with regulators can increase output, reduce costs and simplify start-up and maintenance.