Parts of a Gas Meter – Index, Dials and Diaphragms

All 14 parts on the diagram

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Meter set 5

Regulator (service regulator) It lowers the gas pressure before the meter.
Swivel A short fitting with a nut, joining the meter to the pipe.
Customer piping (house pipes) The pipe from the meter into the building.
Shut-off valve A valve that shuts off the gas supply to the building.
Service pipe (service line) The supply pipe from the gas main, rising out of the ground.

The meter 4

Inlet Gas enters the meter here.
Outlet Measured gas leaves the meter here.
Index The face that shows how much gas has passed through.
Case (casing) The closed metal box that holds the measuring parts.

Index and inside 5

Slide valves They send gas to each side of a diaphragm in turn.
Hand The pointer on a dial; it turns as gas passes.
Dials Round faces that show the gas used, in cubic feet.
Diaphragms (bellows) Flexible walls that fill with gas and empty, like bellows.
Partition The wall down the middle; a diaphragm is fixed to each side.

How this list was compiled: Every name checked on 2026-09-30, a name kept only where two independent sources use it. Wikipedia, Gas meter (https://en.wikipedia.org/wiki/Gas_meter); H. S. Wynkoop, Gas and Gas Meters, Popular Science Monthly, June 1900, as transcribed on Wikisource (https://en.wikisource.org/wiki/Popular_Science_Monthly/Volume_57/June_1900/Gas_and_Gas_Meters); W. P. Gerhard, The American Practice of Gas Piping and Gas Lighting in Buildings (1908), archive.org full text (https://archive.org/details/americanpractice00gerhuoft); C. H. Stone, Practical Testing of Gas and Gas Meters (1909), archive.org full text (https://archive.org/details/practicaltestin00stongoog); US Department of Transportation, Guidance Manual for Operators of Small Gas Systems (1988), archive.org full text (https://archive.org/details/guidance-manual-for-operators-of-small-gas-systems-1988). 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 home gas meter measures the gas a building uses by filling and emptying chambers of a fixed size. The first drawing shows the meter set outside a wall. The second enlarges the index and opens the meter to show what moves inside.

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The meter set

Gas arrives in the service pipe, which rises out of the ground. It passes the shut-off valve and the regulator, which lowers its pressure, and enters the meter through a swivel at the inlet. It leaves at the outlet and runs through the customer piping into the building.

Inside, and on the index

A partition divides the case, with a diaphragm on each side. Slide valves send gas to one side of each diaphragm and then the other, so they fill and empty in turn. That motion turns the hands on the dials of the index.

Questions and answers

What are the parts of a gas meter?

Outside: a case with an inlet and an outlet on top and an index on the front. Inside a diaphragm meter: a partition, diaphragms and slide valves. Around it: the service pipe, a shut-off valve, a regulator and the customer piping.

What is the index on a gas meter?

The index is the face of the meter, where the amount of gas that has passed is shown. On many meters it is a row of small dials, each with a hand. Others show number wheels, like the mileage counter in a car.

How does a diaphragm gas meter work?

Gas fills the space on one side of a flexible diaphragm and pushes out the gas on the other side, then the valves swap the sides. Each fill moves a fixed volume, and the motion is geared to the index.

What does the regulator next to a gas meter do?

It lowers the pressure of the gas coming from the service pipe to the pressure the building uses. The meter sits just after it.