Page 47 - igem-g-4 edition 2

IGEM/G/4 Edition 2
tightness test pressure (TTP)
Pressure to be applied during a tightness test.

tightness test permitted leak rate (TTPLR)
Leak rate permitted during a tightness test and which vary according to the test gas used and
the test pressure.

TN-C-S system
Electrical system in which neutral and protective functions are combined in a single conductor.

trace heating
Provision for supplying heat to prevent the contents of a pipe from changing state.

trenchless technology
Techniques for utility and other line installations, replacement, renovation, inspection, location
and leak detection, with minimum excavation from the ground surface.

turbulent flow
Movement of a fluid in which subcurrents in the fluid display turbulence, moving in irregular
patterns, while the overall flow is in one direction.

turndown
Ratio between the range defined by maximum and minimum flow rates in which the device
indications are not subject to an error greater than the maximum permissible error.

st
two stage pressure reduction (with monitor override on 1 stage)
Arrangement of two regulators in series whose pressure settings are so arranged as to allow a
stepped pressure reduction through the first stage regulator to maintain a controlled pressure
for the second stage regulator, which then controls the final outlet pressure requirement.

U-duct system
Shared/common flue system comprising a duct in the form of a `U’, the vertical limbs being
open at the top and adjacent. One limb provides combustion air, while the other limb, into
which room sealed appliance flues are installed, removes products of combustion.

ultimate limit state
State of a pipeline when it can no longer contain the gas it is carrying.

unconverted index
Index reading displayed on a conversion device which repeats the gas volume recorded by the
meter.

under-pressure tee
Split fitting used to take a branch connection from a pressurised pipe.

usable range
Range claimed by a manufacturer.

utility infrastructure provider (UIP)
Company which designs and installs gas mains and services on behalf of a developer for
adoption by a gas transporter (GT).

valve proving system
System to check the effective closure of a system shut-off valve.

Note: May be used in conjunction with manual or automatic valves.

vapour control layer (VCL)
A membrane fixed to the stud framing, which increases the vapour resistance of the internal
wall face to reduce the transmission of water vapour into the wall panel.

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