Short answer
A gas regulator balances a spring against a diaphragm sensing outlet pressure. When outlet pressure falls because demand increases, the spring pushes the diaphragm and opens the valve to let more gas through; when outlet pressure rises, the diaphragm compresses the spring and closes the valve. Turning the adjustment screw changes spring force and therefore the set point.
Key components
Inlet and outlet body, valve and seat, diaphragm, loading spring, adjustment screw, breather vent and, on larger units, an internal or external impulse line sensing outlet pressure downstream.
Protection devices
Larger regulator installations include over-pressure shut-off (OPSO) and sometimes under-pressure shut-off (UPSO) slam-shut valves, plus relief valves for small over-pressure events. These protect appliances if the regulator fails open and must be reset manually after operating.
Selection
Regulators are selected for inlet pressure range, required outlet pressure, maximum flow and acceptable drop-off. An oversized regulator can be as troublesome as an undersized one, because it works near closed and becomes unstable.
Figures are typical for UK natural gas. The current edition of the relevant IGEM standard and the manufacturer's instructions always take precedence on site.
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