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84
leaks is essential, but ventilation assists the dilution of leaks. Gas detectors can
be provided as an additional precaution.
Domestic credit meters pass up to 101/min, 0.171/s and are 212 mm
wide, 270 mm high and 155 mm deep. Their overall space requirement is ap-
proximately double the width and height measurements for pipework, valve and
filter. Industrial meters have flanged steel pipework up to 100 mm in diameter
and a bypass to allow uninterrupted gas flow in the event of meter breakdown.
A 5001/s meter is 2 m wide, 2.25 m high and 1.6 m deep. Due allowance must
be made for doorways and access for replacing the meter during the building's
use. A separate meter room is recommended, which should be secure, accessi-
ble, illuminated and weatherproof with no hot pipes or surfaces.
Manufactured town gas came from the conversion of coal or oil. It had a
high hydrogen content and flame speed but its cross-calorific value was half
that of methane. In future, substitute natural gas (SNG) may be manufactured
from hydrocarbons as indigenous reserves become exhausted. SNG will come
from the chemical conversion of coal, tar sand or crude oil and will have char-
acteristics similar to those of methane.
Gas pipes or meters should usually be spaced 50 mm from electrical ca-
bles, conduits, telecommunications cables or other conductors. Electric and gas
meters may be accommodated in a single compartment if a fire-resistant parti-
tion separates them.
The meter is divided into three compartments by the horizontal valve
plate near the top and the vertical division plate. Bellows formed by a metal
disc surrounded by a leather diaphragm are located on each side of the division
plate. The gas enters the upper chamber X through the inlet port, from which it
is led to the inside or outside of the bellows depending on the position of the
slide valves.
Gas flow to the appliance causes the bellows to move sideways and this
movement is connected via linked rods, levers and gear wheels to the sliding
valves and the meter dials.
The Gas Act 1986 compels British Gas to supply, and to continue to sup-
ply, gas to any premises within 25 yards (23 m) of a gas-distributing main. The
cost of making a connection, laying the service pipe and maintaining it up to a
maximum length of 9 m on public land is met by British Gas, and any remain-
der on public land, and all on private land, by the applicant.
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