Meter regulators: how they work and how to check them
How a regulator holds outlet pressure steady, what lock-up means, and how regulators fail.
This topic supports
- M04.3Explain how a meter regulator holds outlet pressure steady, and check the operating pressure.
Draft: this lesson hasn't yet been technically reviewed.
The pressure in a low-pressure gas main (up to 75 mbar at the regulator inlet) isn't fixed: it varies with demand on the network. Appliances, though, are designed to run on a steady supply. The sits just upstream of the meter and closes that gap. It lets through only as much gas as it takes to hold the outlet within its working band, whatever the demand.
How it works
Two forces act on the diaphragm. The loading spring pushes it down, which opens the valve. Outlet pressure, fed to the underside of the through the , pushes it back up, which closes the valve. The valve settles wherever the two balance.
- When demand rises, outlet pressure falls slightly. The spring wins, the valve opens further and more gas flows.
- When demand falls, outlet pressure rises, the diaphragm lifts and the valve closes down.
Because the regulator needs a small change in outlet pressure to move the valve, the outlet a little as demand increases. That's why the check range allows readings towards the top at low flow and towards the bottom at high flow. In the model, the outlet sits near 23 mbar at low flow and near 19 mbar at full flow.
Lock-up
With no demand at all, outlet pressure keeps rising until the valve disc seats and no more gas can pass. This is . A regulator that can't lock up, because the disc is worn, damaged or missing, lets the outlet pressure creep up towards the inlet pressure. A lock-up pressure above 30 mbar is a sign of trouble.
Adjustment
Winding the adjusting screw down (clockwise) compresses the loading spring, so more pressure is needed under the diaphragm to close the valve, and the outlet pressure rises. Winding it up lowers the outlet pressure.
How regulators fail
- Ruptured diaphragm. Gas gets into the spring housing above the diaphragm and escapes from the , and the diaphragm can no longer balance outlet pressure against the spring. Regulators are type-tested to limit how much gas can escape this way. In the model, the regulator fails open and the outlet rises towards inlet pressure.
- Detached valve disc. With nothing to close the valve, the regulator can neither regulate nor lock up, and the meter and appliances see the full supply pressure.
- Spring removed. Only the weight of the moving parts pushes the diaphragm down. The regulator still regulates, but to a millibar or two, starving the appliances downstream.
Sources: GSIUR 1998 reg. 14(5)–(7)sealing IGEM/GM/PRS/3 (2022) 5.2, 7.2setting, breather IGEM/G/13 4.1, 5.1–5.218.5–23 mbar, reporting ACS CCN1 Issue 16 §7pressure band ACS CCN1 Issue 16 §16lock-up IGEM/G/11 Ed. 2 Table 1situation 2.2
Checking the itself is covered in 3.3 Standing, working and operating pressure.
Tutor notes
- Before opening the cross section, ask learners to predict what happens to outlet pressure when demand rises, then use the demand slider to check.
- Use the Hole in diaphragm failure to discuss what an engineer would see and smell on site, and what they should do next.
- Ask why the outlet pressure in the model falls slightly at high flow rather than staying at exactly 21 mbar.