This article was updated April 5, 2023. It was originally published Nov. 15, 2002.
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Pressure regulators, more commonly known as pressure-reducing valves, keep the output pressure constant in compressed-air systems no matter how the input pressure or output flow changes. They contain integral loading, sensing, actuating and control components. The regulators are actually a special class of valves that come in a variety of configurations. They are broadly classified as general purpose, special purpose and precision.
General purpose, or utility, regulators have flow and regulation performance that let them meet the requirements of most industrial compressed air applications. They deliver long service lives, simple maintenance and competitive prices.
Special purpose regulators are designed to handle fluids other than compressed air. They can be simple or complex, depending on the specific application and performance requirements.
Precision regulators are applications in which the pressure must be controlled to within close tolerances. They are commonly used when a process or test depends on accurately controlled pressure. The main difference between precision and general-purpose regulators is that the former supplies more control over the accuracy of the output pressure.
All three of these types of regulators operate similarly and use similar loading, actuating, and control components. Most of them rely on simple wire coil springs to control downstream pressure. Various size springs let engineers regulate the pressure to within specific ranges. Ideally, the required pressure should be in the center third of the rated outlet pressure. At the lower end of the pressure range, the spring loses sensitivity; at the high end, the spring nears its maximum capacity.
Regulators use either a piston or diaphragm to sense downstream pressure. Diaphragms are generally more sensitive to changes in pressure and react more quickly. They should be used if pressures of less than 0.04 psi are called for.
Pistons, on the other hand, are more rugged and provide a larger effective sensing area for a given size regulator. Output pressure accuracy is determined by the droop due to flow changes.
Pressure droop is most pronounced when the valve first opens. Factors contributing to droop include changes in the load as the spring extends; changes in the diaphragm’s effective area and with diaphragm displacement; and unbalanced area forces on the valve.
The amount the output pressure changes with variations in supply pressure is called the regulation characteristic. It is affected by the ratio of diaphragm area to valve area and how much the valve is unbalanced.
When selecting pressure regulator, important factors to consider include:
- What is the normal line pressure?
- What are the minimum and maximum regulated pressures required? Regulators can have a wide adjustment range and may need a specific spring or accessory to meet the requirements. Also, minimum and maximum pressure should be within the middle third of the regulator’s range.
- What is the maximum flow needed at the regulated pressure?
- Pipe size: Not all regulators come in all pipe sizes; an adapter might be needed. Also, pipe size should be compatible with flow requirements.
- Regulator adjustments: There are several ways to adjust a regulator. When selecting a regulator, consider where it will be mounted, how it will be adjusted, and who will handling those adjustments.
- How precise does the pressure regulation need to be?
- Will it need accessories or options such as gauges and panel mounting?
- Are there environmental or fluid conditions that could be incompatible with materials used in the regulator?
- Will it need special features such as special lighting or remote control?
- What could happen if the regulator malfunctions or fails? A damper or relief valve might be needed to protect personnel and equipment. Also, dead-end service or intermittent actuation may call for a positive valve shutoff, bleed units or close control of pressure relief points. Filters, lubricators, relief devices and other options should be considered when selecting regulators.