Closed Water Systems; Thermal Expansion - A.O. Smith Lowboy 6 Instruction Manual

paragraph. The new valve must be marked with a maximum set
pressure not to exceed the marked hydrostatic working pressure
of the water heater (150 psi = 1,035 kPa) and a discharge capacity
not less than the water heater Btu/hr or KW input rate as shown on
the water heater's model rating plate.
For safe operation of the water heater, the temperature and pressure
relief valve must not be removed from its designated opening nor
plugged. The temperature-pressure relief valve must be installed
directly into the fitting of the water heater designed for the relief valve.
Install discharge piping so that any discharge will exit only within 6
inches (15.2 cm) above, or at any distance below the structural floor.
Be certain that no contact is made with any live electrical part. The
discharge opening must not be blocked or reduced in size under
any circumstances. Excessive length, over 30 feet (9.14 m), or
use of more than four elbows can cause restriction and reduce the
discharge capacity of the valve.
No valve or other obstruction is to be placed between the relief valve
and the tank. Do not connect discharge piping directly to the drain
unless a 6" (15.2 cm) air gap is provided. To prevent bodily injury,
hazard to life, or property damage, the relief valve must be allowed
to discharge water in adequate quantities should circumstances
demand. If the discharge pipe is not connected to a drain or other
suitable means, the water flow may cause property damage.
The Discharge Pipe:
• Shall not be smaller in size than the outlet pipe size of the valve, or
have any reducing couplings or other restrictions.
• Shall not be plugged or blocked.
• Shall be of material listed for hot water distribution.
• Shall be installed so as to allow complete drainage of both the
temperature-pressure relief valve and the discharge pipe.
• Must terminate a maximum of six inches above a floor drain or
external to the building. In cold climates, it is recommended that the
discharge pipe be terminated at an adequate drain inside the building.
• Shall not have any valve or other obstruction between the relief
valve and the drain.
The temperature-pressure relief valve must be manually operated
at least once a year. Caution should be taken to ensure that (1) no
one is in front of or around the outlet of the temperature-pressure
relief valve discharge line, and (2) the water manually discharged
can cause bodily injury or property damage because the water
may be extremely hot. If after manually operating the valve, it fails
to completely reset and continues to release water, immediately
close the cold water inlet to the water heater, follow the draining
instructions in this manual, and replace the temperature-pressure
relief valve with a properly rated/sized new one.
If you do not understand these instructions or have any questions
regarding the temperature-pressure relief valve call the toll free
number listed on the water heater label for technical assistance.

CLOSED WATER SYSTEMS

Water supply systems may, because of code requirements or such
conditions as high line pressure, among others, have installed
devices such as pressure reducing valves, check valves, and back
flow preventers. Devices such as these cause the water system to
be a closed system.

THERMAL EXPANSION

As water is heated, it expands (thermal expansion). In a closed system
the volume of water will grow when it is heated. As the volume of
water grows there will be a corresponding increase in water pressure
due to thermal expansion. Thermal expansion can cause premature
tank failure (leakage). This type of failure is not covered under the
limited warranty. Thermal expansion can also cause intermittent
temperature-pressure relief valve operation: water discharged from
the valve due to excessive pressure build up. This condition is not
covered under the limited warranty. The temperature-pressure relief
valve is not intended for the constant relief of thermal expansion.
A properly sized thermal expansion tank should be installed on all
closed systems to control the harmful effects of thermal expansion.
Contact a local plumbing service agency to have a thermal expansion
tank installed.
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