Rheem 491 Owner's Manual And Installation Instructions page 35

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EXPANSION CONTROL VALVE
It is mandatory to install an expansion control valve (ECV) in the cold water line
to the water heater to comply with Clause G12 of the New Zealand Building
Code.
The expansion control valve must always be installed after the non-return valve
and be the last valve installed prior to the water heater (refer to the cold water
connection diagram on page 32). A copper drain line must be fitted to the
expansion control valve (refer to "Relief Valve Drain" on page 35).
The valve, if installed within 500 mm of the water heater, must be insulated with
closed cell polymer insulation or similar (minimum thickness 9 mm) and the
insulation installed so as not to impede the operation of the valve. The insulation
must be weatherproof and UV resistant if exposed.
RELIEF VALVE DRAIN
DN15 copper drain lines must be fitted to the temperature pressure relief valve
and expansion control valve (if one is installed) to carry the discharge clear of
the water heater. Connect the drain lines to the valves using disconnection
unions. The drain line from the valve to the point of discharge should be as short
as possible, have a continuous fall all the way from the water heater to the
discharge outlet and have no tap, valves or other restrictions in the pipe work. A
drain line from a relief valve must comply with the requirements of
AS/NZS 3500.4 or Clause G12 of the New Zealand Building Code.
The length of the drain line in metres plus the number of changes in direction
must not exceed twelve (12). For example a drain line nine (9) metres in length
can have no more than three bends before discharging at an outlet or air gap.
The length of a drain line is to be reduced by one (1) metre for each additional
bend required. Where the distance in metres and number of changes in direction
to the point of final discharge exceeds twelve (12), the drain line can discharge
into a tundish.
In New Zealand the drain lines from the temperature pressure relief valve and
expansion control valve from an individual water heater may be interconnected
where freezing is unlikely to occur. The combined drain line must have a
minimum size of DN20 and discharge via a minimum air gap of a minimum
25 mm.
The outlet of a drain line must be in such a position that flow out of the pipe can
be easily seen, but arranged so discharge will not cause injury, damage or
nuisance. The termination point of a drain line must comply with the requirements
of AS/NZS 3500.4. Drain lines must not discharge into a safe tray.
In locations where water pipes are prone to freezing, drain lines must be
insulated, must not exceed 100 mm in length and are to discharge into a tundish
through an air gap of a minimum 25 mm.
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