Relief valveIt opens to let gas out if outlet pressure climbs too high.
InletGas at the higher supply pressure comes in here.
OutletGas leaves here at the lower, set pressure.
Orifice (valve seat)The opening the gas passes through; the disc closes against it.
Valve discIt moves against the orifice to cut down or stop the flow.
Body (valve body)The main casting; the inlet, outlet and valve are in it.
Control side 6
Cap (closing cap)It covers the adjusting screw.
Adjusting screwTurning it changes the spring force, and so the outlet pressure.
SpringIt presses the diaphragm down, which opens the valve.
VentAn opening that keeps the spring side at outside air pressure.
DiaphragmOutlet pressure pushes up on it; the spring pushes down.
Stem (valve stem)It links the diaphragm to the valve disc.
How this list was compiled: Every name checked on 2026-09-30, a name kept only where two independent sources use it. Wikipedia, Pressure regulator (https://en.wikipedia.org/wiki/Pressure_regulator); US Navy, Fluid Power (NAVEDTRA 14105), chapter 6, spring-loaded pressure-reducing valves, as hosted in full text by Engineering Library (https://engineeringlibrary.org/reference/hydraulic-valves-navy); US Department of Energy, DOE Fundamentals Handbook, Mechanical Science, Valves module, reducing valves (https://engineeringlibrary.org/reference/valves-doe-handbook); US Army, TM 9-237, Welding Theory and Application (1967), single stage regulator (https://archive.org/details/TM9-237); a regulator maker's instruction manuals for a spring-loaded regulator and for second-stage regulators (https://archive.org/details/manualzilla-id-7051933, https://archive.org/details/manualzilla-id-7051322, one company, one source); an unrelated seller's two-stage regulator instruction sheet (https://archive.org/details/manualzilla-id-6338979). Licence: own work
The drawing: Drawn for this site on 2026-09-30 from plain geometry; a schematic of no maker's product, nothing traced. Licence: own work
How it works
A pressure regulator takes gas at a high or changing pressure and lets it out at a lower, steady one. The drawing cuts a spring-loaded regulator through, so the diaphragm, the spring and the valve under them all show.
Read the full guide
The gas path
Gas enters the body at the inlet. It rises through the orifice, past the valve disc, into the chamber under the diaphragm, and leaves at the outlet.
How the pressure is held
The spring presses the diaphragm down, and the stem pushes the disc away from the orifice. As outlet pressure builds under the diaphragm it lifts it against the spring, and the disc moves back toward the orifice. The adjusting screw, under its cap, sets the spring. The vent opens the spring side to the air.
Questions and answers
What are the main parts of a pressure regulator?
A body with an inlet and an outlet, a valve between them (an orifice and a disc), a diaphragm that senses the outlet pressure, a spring that loads the diaphragm, and an adjusting screw that sets the spring.
What does the diaphragm do in a regulator?
It compares two forces. Outlet pressure pushes on one side and the spring pushes on the other. When outlet pressure drops, the spring wins and the valve opens wider; when it rises, the valve closes down.
What is the vent on a regulator for?
It is a small opening in the cover over the spring. It keeps that side of the diaphragm at the pressure of the outside air.
What does the adjusting screw do on a regulator?
It sets the outlet pressure. Turning it in presses the spring harder on the diaphragm, so more outlet pressure is needed to close the valve. Turning it out lowers the set pressure.