John Wood Atmospheric Gas (Standard) - Manual (Page 16)

16
METAL
DRAIN PAN
DRAIN
DRAIN LINE 3/4”
ID MINIMUM
DISCHARGE PIPE
DO NOT CAP OR PLUG
TEMPERATURE AND PRESSURE RELIEF (T&P)
VALVE (OPTIONAL TOP T&P RELIEF
VALVE NOT SHOWN)
1” (2.54 cm)
MINIMUM
12” (300 mm)
MAXIMUM AIR GAP
FIGURE 13A.
For protection against excessive pressures and
temperatures, a temperature and pressure relief valve must
be installed in the opening marked “T & P RELIEF VALVE”
(see Figure 13A). This valve must be design certified by
a nationally recognized testing laboratory that maintains
periodic inspection of the production of listed equipment or
materials as meeting the requirements for Relief Valves for
Hot Water Supply Systems, ANSI Z21.22/CSA 4.4-current
edition. The function of the temperature and pressure relief
valve is to discharge water in large quantities in the event
of excessive temperature or pressure developing in the
water heater. The valve’s relief pressure must not exceed
the working pressure of the water heater as stated on the
rating plate.
IMPORTANT: Only a new temperature and pressure relief
valve should be used with your water heater. Do not use an
old or existing valve as it may be damaged or not adequate
for the working pressure of the new water heater. Do not
place any valve between the relief valve and the tank.
The Temperature & Pressure Relief Valve:
•
Must not be in contact with any electrical part.
• Must be connected to an adequate discharge line.
• Must not be rated higher than the working pressure
shown on the rating plate of the water heater.
The Discharge Line:
• Must not be smaller than the pipe size of the relief
valve or have any reducing coupling installed in the
discharge line.
• Must not be capped, blocked, plugged or contain
any valve between the relief valve and the end of the
discharge line.
• Must terminate a maximum of twelve inches (300 mm)
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.
• Must be capable of withstanding 250°F (121°C) without
distortion.
• Must be installed to allow complete drainage of both
the valve and discharge line.
T&P Relief Valve and Pipe Insulation (Some Models)
1. Locate the temperature and pressure relief valve on
the water heater (also known as a T&P relief valve).
See Figure 13B.
2. Locate the slit running the length of the T&P relief
valve insulation.
3. Spread the slit open and fit the insulation over the T&P
relief valve. See Figure 13B. Apply gentle pressure
• It is recommend that only full flow ball or gate valves
are used in water piping installations. The use of valves
that may cause excessive restriction to water flow is not
recommended.
• Use only 95/5 tin-antimony or other equivalent solder.
Any lead based solder must not be used.
• Piping that has been treated with chromates, boiler seal,
or other chemicals must not be used.
• Chemicals that may contaminate the potable water
supply must not be added to the piping system.
Closed System/Thermal Expansion
As water is heated, it expands (thermal expansion). In a
closed system, the volume of water will increase. As the
volume of water increases, 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. The temperature-pressure relief valve is not
intended for the constant relief of thermal expansion. This
condition is not covered under the limited warranty.
A properly-sized thermal expansion tank should be
installed on all closed systems to control the effects of
thermal expansion. Contact a plumbing service agency or
your retail supplier regarding the installation of a thermal
expansion tank.
Temperature and Pressure Relief Valve
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