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PLUMBING CONNECTION
SUMMER 2015 71
escaping combustion products from a balanced flue or
power flue heater into the interior.
Thousands of this type of flued heater have been installed
and should be checked for CO emissions.
OPERATING PRESSURE
Checking the gas operating pressure and supply volume is
crucial to knowing where the problem originates.
In the description of how to conduct a CO test, the
sentence following Clause R1 item C seems to be a
throwaway requirement of the appendix (it is not identified
as a clause or even a note):
“Before these procedures are applied a visual inspection
shall be undertaken to confirm that the appliance and
flue or chimney are clean and unobstructed and installed
correctly.”
This minimum requirement will not suffice for proper gas
appliance servicing, and won’t meet safety requirements
that have been practised for many years.
Gas operating pressure and supply volume should always
be checked before a CO test – let alone when servicing an
appliance. Without the correct settings no appliance will
operate as designed.
This is not my own personal edict but one that can be
traced back several decades to training manuals and
technical papers.
Correct gas volume and operating pressure ensure that
air (containing oxygen) is drawn into the burner for complete
and safe combustion of the gas. Otherwise, the potential for
CO is increased.
As stated in AS/NZS 5601-2013 Clause 5.2.5, Factors
Affecting Air Entrainment, the total volume of air entrained
by a stream depends on the following:
∫ Gas rate;
∫ Gas pressure;
∫ Specific gravity of gas;
∫ Design of the orifice determining the friction loss (injector
size and alignment);
∫ Position of orifice;
∫ Area of opening in shutter (aeration size);
∫ Design of injector tube (venturi design);
∫ Dimension and size of burner head;
∫ Total area of flame ports; and
∫ Temperature of burner head.
The Dux Plumbers Handbook is a comprehensive product and technical guide.
It is a valuable tool which will make it easier than ever to access vital hot water
information on site, right when you need it. The Dux Plumbers Handbook offers:
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specification details
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rough-in diagrams
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