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A
new combination temperature and pressure (T&P)
relief valve, complying with the Standard for Relief
Valves and Automatic Gas Shut-Off Devices for Hot
Water Supply Systems, ANSI Z21.22, must be
installed in the opening provided on top of the storage
tank at the time of installation. No valve is to be placed
between the relief valve and the storage tank.
The pressure rating of the relief valve must not exceed
the 160 maximum working pressure indicated on the
water heater rating plate. The BTUH rating of the relief
valve must not be less than the BTUH input of the
heater.
Connect the outlet of the relief valve to a suitable open
drain. The discharge line must pitch downward from
the valve to allow complete draining (by gravity) of the
relief valve and discharge line. The discharge line
should be no smaller than the outlet of the valve. The
end of the discharge line should not be threaded or
concealed, and should be protected from freezing. No
valve of any type, restriction or reducer coupling,
should be installed in the discharge line. Local codes
shall govern installation of the relief valve.
>69$26..5*B
There are two versions of the Pump Time Delay. The
first is an electronic device that allows the operator to
set a variable time (3 to 10 minutes) for the pump to
run after the heater shuts off. See Fig. 21 (A). The time
is factory-set at 7 minutes and it can be re-adjusted in
the field.
The second version is a fully enclosed solid state Time
Delay Relay (TDR) with a white jumper that selects
one of two time delays. See Fig. 21 (B). If the jumper
is on pins 6 and 7 (default) the delay time is 5 minutes.
If the jumper is not on pins 6 and 7, the time delay is
10 minutes.
In a conventional system, when the tankstat is satis-
fied, the main gas valve closes, but the pump
continues operating. With either time delay relay the
heater pump is programmed to continue running for an
optimum period of time in order to absorb the residual
heat from the combustion chamber and use it in the
system. The pump then shuts off until the next call for
heat is received from the tankstat.
5.,=;872,072=287
The intermittent ignition device conserves energy by
automatically extinguishing the pilot when desired
temperature is reached. When additional heat is need-
ed, the pilot re-ignites electrically, eliminating the fuel
costs of maintaining a constant pilot. To ensure safe
operation, the gas valve cannot open until the pilot
relights and is confirmed.
9.;*=27087=;85<
On models 0514-1826, models with mechanical mod-
ulating controls have one or more Robertshaw Unitrol
7000 Series hydraulic snap on thermostatic combina-
tion gas valves. These valves have the pressure
regulator and 24-volt operator built-in. The hydraulic
actuator will throttle the heater input to adjust the firing
rate and meet the required load. This, in effect, pre-
vents costly fuel consumption, as compared to an
$ Pump will come on when power is first
applied to heater.
Fig. 21: Economaster Time Delay Relays (TDR)
6
1
2
(A)
(B)
Table J: Electronic Ignition