By Gregory Havel
Although firefighters do notserviceor installnatural gasmeters, piping, and regulators, they need an understanding of how these devicesworkso that they can work moresafely.
Photo 1 shows the natural gas meter and regulators located at aschool. This setup is typical of smallcommercialmeters and regulators, although there will be somevariationin appearance andoperatingpressuresbetween areas supplied by differentgascompanies. There may also be some variation between areas requiring compliance with NFPA 54,National Fuel Gas Code,2012 edition (ASTM Z223.1—2012), and areas requiring compliance with otherstandards.
In Photo 1, the gas from thegasmain enters the meter and regulators at the “servicevalve” at a pressure of 50 to 75 pounds per square inch (psi) (3.515-5.273 kg/cm2) or higher. This is the valve that is most important to close if we are ordered to shut off the gas to thebuilding. This valve has a ring cast onto the side of its body and the square or rectangular head on the valve has a tab with a matching ring. When the ring on the head is in line with thepipe, the valve is open. A quarter turn of the head of the valve will close the valve; line up the ring on the head with the ring on the body so that a lock or seal can be applied to prevent the valve from being opened.
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After the gas passes through the service valve, it passes through the first “regulator” (at the left in photo 1), where its pressure is reduced to 25-30 psi (1.758-2.109 kg/cm2) for metering. The pipe entering the regulator is smaller than the pipe leaving the regulator to compensate for the pressurereductionin the regulator. (Natural gas is distributed in gas mains athigh pressuresin relatively small pipes and are reduced in pressure at regulators at gas meters with an increase in pipe size so that the same amount ofheatenergy will be available; pressure is reduced again inside the building to the pressure needed by each appliance.) Then, it passes through the strainer (S), which remove any particles or condensed moisture to protect themechanismin the gas meter.
The gas passes down through the first meter valve (MV)—which is normally open—and through the gas meter, where itsvolumeis measured so that thecustomercan be billed accurately. The gas passes through the second MV (which is also normally open) and up and to the right to the second regulator, where the gas pressure is reduced to no more than 5 psi (0.352 kg/cm2) for safe distribution inside the building.
The bypass valve (BV) is normally closed and locked. This valve is installed in larger gas meter sets so that the meter can be serviced or replaced without shutting off the gas to the building. When servicing or replacing the meter, the gas companytechnicianwill unlock and open the BV, close both meter valves, service or replace the meter, open the meter valves and close the BV, check forleaks, and lock the BV.
Piping to the service valve may be plastic while it isunderground. The piping connecting the valves, regulators, and gas meter is usuallysteel, as is the pipe through thewallfrom the meter and regulators into the building. Steel is used becausestrengthis needed to support the weight of theequipment和抵抗气体的压强inside the pipe. Once the pipe is inside the building, it may be steel, corrugated stainless-steel tube (CSST), or another material permitted by thecodesand authority having jurisdiction that is resistant to any corrosive impurities in the natural gas in the area.
For more information on the use of CSST, see “Construction Concerns” dated May 13, 2009, or clickHERE.
白色的管道图1所示是PVC塑料nd is connected to the regulator vents. Regulators have vent connections to the atmospheric side of their diaphragms so there will be no back pressure generated; the amount of gas flowing changes the position of the diaphragm so that any gas leaks around or through the diaphragm are carried away from the area of the regulator. These vent pipes extend away from the regulators to a location that is a specifieddistancefrom theground;windows; entrances; andheating, venting, and air-conditioningvents (photo 2).
PHOTO 2.
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Larger regulators inside the building also need vent piping. The white plastic pipe that runs from the far right in photo 1 to the left in photo 2 is connected to the regulator for theboilersin the school basement. This pipe is steel inside the building and through the exterior wall. Plastic regulator vent piping is not permitted inside buildings by NFPA 54.
Under the conditions specified in NFPA 54, two or more regulators can share a vent pipe, as shown in the two photos.
For detailed information on these requirements, see NFPA 54National Fuel Gas Code,2012 edition, Chapter 5:
- Piping: Sections 5 and 6
- Meters: Section 7
- Regulators: Section 8
- Regulator vents: Section 9
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Gregory Havelis a member of the Town of Burlington (WI) Fire Department; retired deputy chief and training officer; and a 30-year veteran of the fire service. He is a Wisconsin-certified fire instructor II, fire officer II, and fire inspector; an adjunct instructor in fire service programs at Gateway Technical College; and safety director for Scherrer Construction Co., Inc. Havel has a bachelor’s degree from St. Norbert College; has more than 30 years of experience in facilities management and building construction; and has presented classes at FDIC.
