Temperature-Pressure Relief Valve - A.O. Smith PXHT Instruction Manual

This water heater shall not be connected to any heating systems or
component(s) used with a non-potable water heating appliance.
Toxic chemicals, such as those used for boiler treatment shall not be
introduced into this system.
Water supply systems may, because of such events as high line
pressure, frequent cut-offs, the effects of water hammer among
others, have installed devices such as pressure reducing valves, check
valves, back flow preventers, etc. to control these types of problems.
When these devices are not equipped with an internal by-pass, and no
other measures are taken, the devices cause the water system to be
closed. As water is heated, it expands (thermal expansion) and closed
systems do not allow for the expansion of heated water.
The water within the water heater tank expands as it is heated and
increases the pressure of the water system. If the relieving point of
the water heater's temperature-pressure relief valve is reached, the
valve will relieve the excess pressure. The temperature-pressure
relief valve is not intended for the constant relief of thermal
expansion. This is an unacceptable condition and must be corrected.
It is recommended that any devices installed which could create a
closed system have a by-pass and/or the system have an expansion
tank or device to relieve the pressure built by thermal expansion in the
water system. Expansion tanks are available for ordering through a
local plumbing contractor. Contact the local water supplier and/or a
service agency for assistance in controlling these situations.
NOTE: To protect against untimely corrosion of hot and cold
water fittings, it is strongly recommended that di-electric
unions or couplings be installed on this water heater when
connected to copper pipe.
FIGURE 4.
Figure 4 shows the typical attachment of the water piping to the water
heater. The water heater is equipped with 3/4 inch NPT water
connections.
NOTE: If using copper tubing, solder tubing to an adapter
before attaching the adapter to the cold water inlet connection.
Do not solder the cold water supply line directly to the cold
water inlet, it will harm the dip tube and damage the tank.

TEMPERATURE-PRESSURE RELIEF VALVE

This heater is provided with a properly certified combination
temperature - pressure relief valve by the manufacturer.
The valve is certified by a nationally recognized testing laboratory that
maintains periodic inspection of production of listed equipment of
materials as meeting the requirements for Relief Valves and Automatic
Gas Shut-off Devices for Hot Water Supply Systems, ANSI Z21.22 •
CSA 4.4, and the code requirements of ASME.
If replaced, the valve must meet the requirements of local codes, but
not less than a combination temperature and pressure relief valve
certified as indicated in the above paragraph.
The 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 input rate as shown on the model rating plate.
For safe operation of the water heater, the 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. Position the
valve downward and provide tubing so that any discharge will exit
only within 6 inches (153 mm) 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 tubing directly to discharge drain unless
a 6 inch air gap is provided. To prevent bodily injury, hazard to life, or
property damage, the relief valve must be allowed to discharge water
in 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.
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