A.O. Smith 400A - Manual (Page 16)

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To prevent damage, care must be taken not to apply too much torque
when attaching gas supply pipe to gas valve inlet.
Apply joint compounds (pipe dope) sparingly and only to the
male threads of pipe joints. Do not apply compound to the first
two threads. Use compounds resistant to the action of liquefied
petroleum gases.
DISCONNECT THE APPLIANCE AND ITS MANUAL GAS
SHUTOFF VALVE FROM THE GAS SUPPLY PIPING SYSTEM
DURING ANY SUPPLY PRESSURE TESTING EXCEEDING 1/2
PSIG (3.45Kpa). GAS SUPPLY LINE MUST BE CAPPED WHEN
DISCONNECTED FROM THE HEATER. FOR TEST PRESSURES
OF 1/2 PSIG (3.45Kpa) OR LESS, THE APPLIANCE NEED NOT
BE DISCONNECTED, BUT MUST BE ISOLATED FROM THE
SUPPLY PRESSURE TEST BY CLOSING THE MANUAL GAS
SHUTOFF VALVE.
BEFORE PLACING THE HEATER IN OPERATION, CHECK FOR
GAS LEAKAGE. USE SOAP AND WATER SOLUTION OR OTHER
MATERIAL ACCEPTABLE FOR THE PURPOSE OF LOCATING
GAS LEAKS. DO NOT USE MATCHES, CANDLES, FLAME OR
OTHER SOURCES OF IGNITION FOR THIS PURPOSE.
PURGING
Gas line purging is required with new piping or systems in which
air has entered.
CAUTION
PURGING SHOULD BE PERFORMED BY PERSONS EXPERIENCED
IN THIS TYPE OF GAS SERVICE. TO AVOID RISK OF FIRE OR
EXPLOSION, PURGE DISCHARGE MUST NOT ENTER CONFINED
AREAS OR SPACES WHERE IGNITION CAN OCCUR. THE AREA
MUST BE WELL VENTILATED AND ALL SOURCES OF IGNITION
MUST BE INACTIVATED OR REMOVED.
GAS METER SIZE - CITY GASES ONLY
Be sure that the gas meter has sufficient capacity to supply the full
rated gas input of the water heater as well as the requirements of
all other gas fired equipment supplied by the meter. If the gas meter
is too small, ask the gas company to install a larger meter having
adequate capacity.
GAS VALVES
WARNING
SHOULD OVERHEATING OCCUR OR THE GAS SUPPLY FAIL
TO SHUT OFF, TURN OFF THE MANUAL GAS CONTROL VALVE
TO THE APPLIANCE.
SYSTEM CONNECTIONS
The system installation must conform to these instructions and to
the local code authority having jurisdiction. Good practice requires
that all heavy piping be supported.
THERMOMETERS (Not Supplied)
Thermometers should be obtained and field installed as shown in
the installation diagrams.
Thermometers are installed in the system as a means of detecting
the temperature of the outlet water supply.
RELIEF VALVE
This heater is equipped with an approved temperature and pressure
relief valve. ASME ratings cover pressure relief. CSA ratings cover
release rate with temperature actuation.
FOR SAFE OPERATION OF THE WATER HEATER, THE RELIEF
VALVE(S) MUST NOT BE REMOVED OR PLUGGED.
In addition to the appliance relief valve, each remote storage tank
which may be used in conjunction with this appliance shall also be
installed with a properly sized, rated and approved temperature
(ANSI) and pressure (ASME) relief valve(s). This relief valve shall
comply with the standard for relief valves and automatic gas shutoff
devices for hot water supply systems. ANSI Z21.22-CSA 4.4.
Your local code authority may have other specific relief valve
requirements.
WARNING
THE PURPOSE OF A RELIEF VALVE IS TO AVOID EXCESSIVE
PRESSURE OR TEMPERATURE INTO THE STEAM RANGE,
WHICH MAY CAUSE SCALDING AT FIXTURES, TANK EXPLOSION,
SYSTEM OR HEATER DAMAGE. NO VALVE IS TO BE PLACED
BETWEEN THE RELIEF VALVE AND THE TANK.
A DRAIN LINE MUST BE CONNECTED TO THE RELIEF VALVE
TO DIRECT DISCHARGE TO A SAFE LOCATION TO AVOID
SCALDING OR WATER DAMAGE. THIS LINE MUST NOT BE
REDUCED FROM THE SIZE OF THE VALVE OUTLET AND MUST
NOT CONTAIN VALVES OR RESTRICTIONS, NOR SHOULD IT BE
LOCATED IN FREEZING AREAS. DO NOT THREAD OR CAP THE
END OF THIS LINE. RESTRICTED OR BLOCKED DISCHARGE
WILL DEFEAT THE PURPOSE OF THE VALVE AND IS UNSAFE.
THE DISCHARGE LINE SHALL BE INSTALLED TO ALLOW
COMPLETE DRAINAGE OF BOTH THE VALVE AND LINE.
WATER LINE CONNECTIONS
This manual provides detailed installation diagrams (see back
section of this manual) for typical methods of application for the
water heaters.
The water heater may be installed by itself, or with a separate storage
tank. When used with a separate storage tank, the circulation may be
either by gravity or by means of circulating pump. When a circulating
pump is used, it is important to note that the flow rate should be slow
so that there will be a minimum of turbulence inside the heater.
CLOSED SYSTEM
CAUTION
A closed system will exist if a check valve (without bypass), pressure
reducing valve (without bypass), or a water meter (without bypass) is
installed in the cold water line between the water heater and street
main (or well).
Excessive pressure may develop causing premature tank failure or
intermittent relief valve operation. This type of failure is not covered
by the limited warranty. An expansion tank or a similar device may
be required in the inlet supply line between the appliance and the
meter or valve to compensate for the thermal expansion of water
under supply pressure.
If a water heater is installed in a closed water system, check local