Air pressure regulators control the pressure in air lines used by pneumatic tools and machines. To provide consistent pressures, they remove fluctuations in the air supply and are adjustable. The reduction in pressure is the key characteristic of pressure regulators; outlet pressure is always less than the inlet pressure. The applications for air pressure regulators vary considerably. Air pressure regulators are found in many common applications such as in gas grills, propane pressure control, and in medical/dental equipment to regulate oxygen and anesthesia gases.

Three functional elements comprise: a pressure regulator. A pressure reducing element, a sensing element, and a reference force element. When operating, the force element produces a force that opens the reducing element. Pressure introduced into the inlet port then flows through the valve and presses against the sensing element. The regulated pressure acts on the sensing element to produce a force opposing the spring force and closes the valve.

The sensing element is most commonly a piston or diaphragm. Pistons are best for higher outlet pressures and when outlet pressures are not held to a tight tolerance. Diaphragms are used for increased accuracy in low pressure applications.

Types of Air Pressure Regulators

There are several types of air pressure regulators.

• General purpose regulators are designed for typical industrial use and operate above atmospheric pressure.
• High pressure regulators are rated for inlet pressures over 1000 psi, and low pressure regulators operate at pressures below 15–20 psi.
• With dual stage regulators, fluid flows through successive chambers so that a constant pressure is delivered even when the inlet pressure decreases.
• Point-of-use regulators attach at or near a tool or device.

Additional descriptions for types of regulators can be found here.

Specifications

Pressure and Flow Requirements

When selecting an air pressure regulator it is important to consider the range of fluctuation in the inlet pressure, as well as the required outlet pressure. The possible variation in flow rate should also be considered to ensure the regulator will not fail in the desired application. Too much or too little pressure can cause the regulator to malfunction.

Adjustment

Air pressure regulators provide several methods of adjustment control. Manual regulators typically use knobs or T-handles. Analog voltage controls cover ranges such as 0–5V and 0–10V, while analog current controls are designed for current loops such as 4–20mA. Pneumatic adjustment controls or “volume boosters” control air inputs. Some adjustment controls include serial, parallel, or digital interfaces.

Additional adjustments  can be made by changing the orifice size. Increasing the valve port size can increase flow. If the port orifice becomes too big it can cause fluctuations in the inlet pressures (excessive droop/rise).

Accuracy

The accuracy of a regulator is observed by charting a given outlet pressure versus flow rate. The resulting chart shows a reduction in the outlet pressure as the flow rate increases, a phenomenon known as droop. Droop is further defined as when the outlet pressure drops below the set point as flow increases. Accuracy and capacity is noted by the amount of droop for a given range of flows. Before selecting a pressure regulator, the performance curve should be carefully examined to ensure the regulator meets the performance requirements.

Mounting Options

There are several ways to mount air pressure regulators.

• Cartridge-mounted regulators insert, screw in, or slip into place so that operators may remove them and gain access to valve components.
• Multiple valve modules stack into an assembly and contain integral circuit flow paths to reduce system piping.

Materials

Air pressure regulators use several types of body materials.

Acetal polymers offer excellent inherent lubricity and provide both fatigue resistance and chemical resistance. Plastics are suitable for many medical procedures involving bodily fluids. They are often ideal for throw away applications.

Aluminum is very light weight, resistant to oxidation, and has good electrical and thermal conductivity.

Brass also provides good conductivity, as well as excellent high temperature ductility and reasonable cold ductility.

Cast iron is composed primarily of iron, but also has important trace amounts of carbon and silicon.

Steel, a commercial iron that contains carbon as an essential alloying constituent, has less carbon than cast iron and is malleable.

Stainless steel is chemical and corrosion resistant and is rated for high pressures. This is the best material for clean rooms and corrosive fluids.

Zinc, a crystalline metallic element, becomes ductile with slight heating but is brittle at ordinary temperatures.

Brass, aluminum, and plastic are the least expensive options.

Some air pressure regulators are equipped with an internal pressure gage or a bleed-off valve for pressure relief. Others have an integral filter for fluid intake or an attached lubricator for valve operation. Tamper-proof air pressure regulators have security devices such as locks to prevent unwanted adjustment.

Standards

Air pressure regulators must adhere to specific standards to ensure proper design and functionality. These standards include BS ISO 6953-1, which discusses compressed air pressure regulators and filter regulators. Also of note are ISO 6953-2 and ISO 6953-3, which include information on test methods for air pressure regulators.

References

The Basics of Pressure Regulators

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