John Wood Atmospheric Vent Light-Duty - Manual (Page 6)

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Temperature and Pressure Relief
Valve(T&P)
For protection against excessive water pressure and/or
temperatures, a temperature and pressure relief valve must be
installed in the opening marked, “T&P VALVE”. Pressure rating of
the valve must not exceed the maximum working pressure shown
on the rating plate of the water heater. The discharge capacity
must be equal to or greater than the BTU input to the water heater.
Relief valve piping must terminate to a floor drain or external to the
building. Do not thread cap or plug the end of this discharge line.
Be certain that no contact is made with any live electrical part or
gas piping (see figure 4). The function of the temperature and
pressure relief valve is to discharge water in quantities should
circumstances demand. If the discharge pipe is not directed to a
drain as shown in figure 4 or other suitable means, the water flow
may cause property damage.
The discharge line:
1 must not be smaller than the outlet pipe size of the relief
valve,
2 must not be plugged, blocked, allowed to freeze or be
restricted in any way,
3 must be of material capable of withstanding 210 O F(100 O C)
without distortion,
4 must be installed so as to allow complete drainage of both the
temperature and pressure relief valve and discharge line,
5 must terminate at an adequate drain, and
6 must not have any valve between the relief valve and the
water heater.
PRESSURE BUILD-UP IN A WATER
SYSTEM (Thermal Expansion)
During the heating cycle of the water heater, the water expands
and creating a pressure build-up in the water system. The water
supply meter may contain a check valve or back flow preventer.
This will create a closed water system, the relief valve will
discharge water as the volume of water expands with rising water
temperature. This is normal and indicates a normal functioning of
the relief valve. Do not plug the temperature and pressure relief
valve. Only if the discharge from the valve is continuous or for an
extended period of time would this indicate a malfunction. Have
the operation of the heater checked by a qualified technician.
Closed systems require the installation of an expansion tank as
shown in figure 4.
V) VENTING
Install the draft hood to the top of the heater as shown in figure 6.
The vent pipe (flue pipe) must be installed without restriction or
reduction in size.
Slope the horizontal run upward to the chimney at least 1/4” per
foot (21mm per meter). Fasten all joints with sheet metal screws.
Once the heater has been put into service check that the venting
is operating properly by checking for spillage at the draft hood.
This test must be performed with;
1. all windows and doors closed,
2. all exhaust fans on,
3. and all fuel fired appliances on.
If spillage occurs, disconnect the water heater and have the
installation inspected and corrected by a qualified technician.
These conditions must be corrected since persistent back draft
may pose a safety hazard and can cause nuisance shut downs.
Installation Check List
1. Has the gas piping been leak tested and no leaks found?
2. Does the gas piping conform with the recommendations of
the Gas Utility Company or the authority having jurisdiction?
3. Is there at least a 1”(25mm) clearance between the water
heater and combustible material, 8”(200mm) at the top and
4”(100mm) in front for closet installation? See figure 1and table 1.
4. Does the area around the heater have adequate ventilation
and air supply?
5. Is the draft hood and vent pipe installed properly and in good
condition?
6. Is the draft hood relief opening and venting unobstructed?
7. Were steps taken to prevent water damage in case of leaks?
8. Is there a temperature and pressure relief valve installed?
9. Is the drain-pipe from the temperature and pressure relief
valve unobstructed?
10. Is the water heater completely filled with water?
If the answer to all of the questions above is “yes”,
proceed with lighting the heater.
WARNING!
Do not attempt to operate this water heater with the cold
water inlet valve closed.
Check Here
Figure 6
Figure 7
Figure 5