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Start Up Conditions
Thermal Expansion
Water supply system may, because of such events as high line
pressure, frequent cut-offs, and the effects of water hammer have
installed devices such as pressure reducing valves, check valves,
back fl ow 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 water heater's temperature-pressure relief valve is reached,
the valve will relief 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. Thermal expansion tanks are available from
Sears stores and through the Sears Service Centers. Contact
the local plumbing inspector, water supplier and/or the Sears
Service Center for assistance in controlling these situations.
See Figure 26.
Thermal Expansion Tank Specifi cations
Tank
Model
Capacity
Number
In Gallons
Diameter
153.331020
2
8 (203 mm) 12-3/4 (323 mm) 3/4" Male
153.331050
5
11 (279 mm) 14-3/4 (375 mm) 3/4" Male
Expansion Tank Sizing Chart
Inlet*
Water
Pressure
Expansion
40psi
Tank
50psi
Capacity
60psi
Needed
70psi
80psi
*Highest recorded inlet water pressure in a 24 hour period or
regulated water pressure.
Dimensions
Pipe
in Inches
Fitting
Length
On Tank
Water Heater Capacity (Gallons)
30
40
50
66
2
2
2
5
2
2
2
5
2
2
5
5
2
2
5
5
2
5
5
5
NOTE: Expansion tanks are pre-charged with a 40 psi air
charge. If the inlet water pressure is higher than 40 psi, the
expansion tank's air pressure must be adjusted to match
that pressure, but must not be higher than 80 psi.
Strange Sounds
Possible noises due to expansion and contraction of some metal
parts during periods of heat-up and cool-down do not represent
harmful or dangerous conditions.
Condensation causes sizzling and popping within the burner area
during heating and cooling periods and should be considered
normal. See Condensation section.
80
Draft Hood Operation
5
Check draft hood operation by performing a worst case
5
depressurization of the building. With all doors and windows
5
closed, and with all air handling equipment and exhaust fans
5
operating such as furnaces, clothes dryers, range hoods and
5
bathroom fans, a match fl ame should still be drawn into the draft
hood of the water heater with its burner fi ring. If the fl ame is not
drawn toward the draft hood, shut off water heater and make
necessary air supply changes to correct.
23
FIGURE 26.
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