# Pressure regulator

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Oxygen and MAPP gas cylinders with two-stage pressure regulators

A pressure regulator is a control valve that reduces the input pressure of a fluid to a desired value at its output. Regulators are used for gases and liquids, and can be an integral device with an output pressure setting, a restrictor and a sensor all in the one body, or consist of a separate pressure sensor, controller and flow valve.

## Operation

A pressure regulator's primary function is to match the flow of gas through the regulator to the demand for gas placed upon it, whilst maintaining a constant output pressure.

If the load flow decreases, then the regulator flow must decrease as well. If the load flow increases, then the regulator flow must increase in order to keep the controlled pressure from decreasing due to a shortage of gas in the pressure system.

A pressure regulator includes a restricting element, a loading element, and a measuring element:

• The restricting element is a valve that can provide a variable restriction to the flow, such as a globe valve, butterfly valve, poppet valve, etc.
• The loading element is a part that can apply the needed force to the restricting element. This loading can be provided by a weight, a spring, a piston actuator, or the diaphragm actuator in combination with a spring.
• The measuring element functions to determine when the inlet flow is equal to the outlet flow. The diaphragm itself is often used as a measuring element; it can serve as a combined element.

In the pictured single-stage regulator, a force balance is used on the diaphragm to control a poppet valve in order to regulate pressure. With no inlet pressure, the spring above the diaphragm pushes it down on the poppet valve, holding it open. Once inlet pressure is introduced, the open poppet allows flow to the diaphragm and pressure in the upper chamber increases, until the diaphragm is pushed upward against the spring, causing the poppet to reduce flow, finally stopping further increase of pressure. By adjusting the top screw, the downward pressure on the diaphragm can be increased, requiring more pressure in the upper chamber to maintain equilibrium. In this way, the outlet pressure of the regulator is controlled.

${\displaystyle F=(P_{i}-P_{o})s+P_{o}S+f}$
${\displaystyle F:\ diaphragm\ spring\ force}$

${\displaystyle f:\ poppet\ spring\ force}$
${\displaystyle P_{i}:\ inlet\ pressure}$
${\displaystyle P_{o}:\ outlet\ pressure}$
${\displaystyle s:\ poppet\ area}$

${\displaystyle S:\ diaphragm\ area}$
Single-stage pressure regulator
Two-stage pressure regulator

### Single stage regulator

High pressure gas from the supply enters into the regulator through the inlet valve. The gas then enters the body of the regulator, which is controlled by the needle valve. The pressure rises, which pushes the diaphragm, closing the inlet valve to which it is attached, and preventing any more gas from entering the regulator.

The outlet pressure and the inlet pressure hold the diaphragm/poppet assembly in the closed position against the force of the large spring. If the supply pressure falls, it is as if the large spring compression is increased allowing more gas and higher pressure to build in the outlet chamber until an equilibrium pressure is reached. Thus, if the supply pressure falls, the outlet pressure will increase, provided the outlet pressure remains below the falling supply pressure. This is the cause of end-of-tank dump where the supply is provided by a pressurized gas tank. With a single stage regulator, when the supply tank gets low, the lower inlet pressure causes the outlet pressure to climb. If the spring compression is not adjusted to compensate, the poppet can remain open and allow the tank to rapidly dump its remaining contents. In other words, the lower the supply pressure, the lower the pressure differential the regulator can achieve for a given spring setting.

The outlet side is fitted with a pressure gauge. As gas is drawn from the outlet side, the pressure inside the regulator body falls. The diaphragm is pushed back by the spring and the valve opens, letting more gas in from the supply until equilibrium is reached between the outlet pressure and the spring. The outlet pressure therefore depends on the spring force, which can be adjusted by means of an adjustment handle or screw.

### Double stage regulator

Two stage regulators are two single stage regulators in one that operate to reduce the pressure progressively in two stages instead of one. The first stage, which is preset, reduces the pressure of the supply gas to an intermediate stage; gas at that pressure passes into the second stage. The gas now emerges at a pressure (working pressure) set by the pressure adjusting control knob attached to the diaphragm. Two stage regulators have two safety valves, so that if there is any excess pressure there will be no explosion. A major objection to the single stage regulator is the need for frequent adjustment. If the supply pressure falls, the outlet pressure may change, necessitating adjustment. In the two stage regulator, there is improved compensation for any drop in the supply pressure.

## Applications

### Air compressors

Air compressors are used in industrial, commercial, and home workshop environments to perform an assortment of jobs including blowing things clean; running air powered tools; and inflating things like tires, balls, etc. Regulators are often used to adjust the pressure coming out of an air receiver (tank) to match what is needed for the task. Often, when one large compressor is used to supply compressed air for multiple uses (often referred to as "shop air" if built as a permanent installation of pipes throughout a building), additional regulators will be used to ensure that each separate tool or function receives the appropriate pressure it needs. This is important because some air tools, or uses for compressed air, require pressures that may cause damage to other tools or materials.

### Aircraft

Pressure regulators are found in aircraft cabin pressurization, canopy seal pressure control, portable water systems, and waveguide pressurization.[1]

### Aerospace

Aerospace pressure regulators have applications in propulsion pressurant control for reaction control systems (RCS) and Attitude Control Systems (ACS), where high vibration, large temperature extremes and corrosive fluids are present.[2]

### Cooking

All modern pressure cookers will have a pressure regulator valve and a pressure relief valve as a safety mechanism to prevent explosion in the event that the pressure regulator valve fails to adequately release pressure. Some older models lack a safety release valve[citation needed]. Most home cooking models are built to maintain a low and high pressure setting. These settings are usually between 7 and 15 PSI. Almost all home cooking units will employ a very simple single-stage pressure regulator. Older models will simply use a small weight on top of an opening that will jiggle to allow excess pressure to escape. Newer models usually incorporate a spring-loaded valve that lifts and allows pressure to escape as pressure in the vessel rises. Some pressure cookers will have a quick release setting on the pressure regulator valve that will, essentially, lower the spring tension to allow the pressure to escape at a quick, but still safe rate. Commercial kitchens also use pressure cookers, in some case using oil based pressure cookers to quickly deep fry fast food. In this case, and in the case of cooking at home, pressurized vessels can be used to cook food much more rapidly than it would take to cook large amounts of food without pressure. Pressure vessels of this sort can also be used to sterilize small batches of equipment and in home canning operations.

### Water pressure reduction

Often, water enters water-using appliances at fluctuating pressures, especially in remote locations, and industrial settings. This pressure often needs to be kept within a range to avoid damage to appliances, or accidents involving burst pipes/conduits. A single-stage regulator is sufficient in accuracy due to the high error tolerance of most such appliances. Also used in applications where the water supply reservoir is significantly higher in elevation to the end of the line. e.g. underground mine water supply.

### Oxy-fuel welding and cutting

Oxy-fuel welding and cutting processes require gases at specific pressures, and regulators will generally be used to reduce the high pressures of storage cylinders to those usable for cutting and welding. Oxy-gas regulators usually have two stages: The first stage of the regulator releases the gas at a constant rate from the cylinder despite the pressure in the cylinder becoming less as the gas is released. The second stage of the regulator controls the pressure reduction from the intermediate pressure to low pressure. It is constant flow. The valve assembly has two pressure gauges, one indicating cylinder pressure, the other indicating hose pressure.

### Propane/LP Gas

All propane and LP Gas applications require the use of a regulator. Because pressures in propane tanks can fluctuate significantly, regulators must be present to deliver a steady flow pressure to downstream appliances. These regulators normally compensate for tank pressures between 30 - 200PSI (~ 2 - 14 Bar) and commonly deliver 11 inches water column (0.4 PSI or ~ 28 mbr / millibars) for residential applications and 35 inches of water column (1.3 PSI or ~ 90 mbr.) for industrial applications. Propane regulators differ in size and shape, delivery pressure and adjustability, but are uniform in their purpose to deliver a constant outlet pressure for downstream requirements. As is the case in all regulators, outlet pressure is lower than inlet pressure. Common international settings for domestic LP Gas regulators are 28 mbr for butane & 37 mbr for propane.

### Gas powered vehicles

No matter what type of motor (internal combustion engine or fuel cell electric powertrain) a specific pressure regulator will be necessary to bring the stored gas (CNG, Hydrogen) pressure from 700, 500, 350 or 200 bar (or 70, 50, 35 and 20 MPa) to operating pressure in addressing all safety and operational requirements.

### Recreational vehicles

For recreational vehicles with plumbing, a pressure regulator is a necessity. When camping, a source of water may have an enormous pressure level, particularly if it comes from a tank that is at a much higher elevation than the campground. Water pressure is dependent on how far the water must fall. Without a pressure regulator, the intense pressure encountered at some campgrounds in mountainous areas may be enough to burst the camper's water pipes or unseat the plumbing joints, causing flooding. Pressure regulators for this purpose are typically sold as small screw-on accessories that fit inline with the hoses used to connect an RV to the water supply, which are almost always screw-thread-compatible with the common garden hose.

### Breathable air supply

Pressure regulators are used with air tanks for SCUBA diving. The tank may contain pressures well in excess of 2,000 PSI, which could cause a fatal barotrauma injury to a person breathing it directly. A regulator allows only a sustained flow of air at the ambient pressure (which varies by depth in the water).

### Mining Industry

As the pressure builds rapidly in relation to depth, underground mining operations require a fairly complex water system with pressure reducing valves. These devices must be installed at a certain distance interval, usually 600 feet (180 m).[citation needed] Without such valves, pipes would easily burst and pressure would be too great for equipment operation.

### Natural Gas Industry

Pressure regulators are used extensively within the Natural Gas industry. Natural gas is compressed to high pressures in order to be distributed throughout the country through large transmission pipelines. The transmission pressure can be over 1000 psig and must be reduced through various stages to a usable pressure for industrial, commercial, and residential applications. There are three main pressure reductions locations in this distribution system. The first reduction is located at the city gate, whereas the transmission pressure is dropped to a distribution pressure to feed throughout the city. This is also the location where the odorless natural gas is odorized with mercaptan. The distribution pressure is further reduced at a district regulator station, located at various points in the city, to below 60 psig. The final cut would occur at the end users location. Generally, the end user reduction is taken to low pressures ranging from 0.25 psig to 5 psig. Some industrial applications can require a larger usable pressure.