Specifications

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vi) A drain value that allows us to drain the tank to replace the elements or move the tank
vii) A pressure relief valve to control the water pressure inside the tank and thus keeps
the tank form exploding.
viii)A sacrificial anode rod to help keep the steel tank form corroding.
Working : This water heater uses nothing more than the “heat rises” principle to separate hot
water from cold water in the tank. When electric supply is given to the heating element, it
produces heat and hence water gets heated. As cold water comes in, it remains at the bottom
of the tank because it is denser than hot water. The thermostat controls the temperature water
inside the tank. It is generally recommended to keep the temperature between 120 to 140 degrees
F (49 to 60
o
C) to prevent scalding and to save energy. The thermostatic switch disconnects the
supply when the predetermined value of temperature is reached and reconnects the supply
when temperature comes down. Normally the thermostat is underneath a cover plate and it has
a knob or a screw to set the temperature.
Pressure type : When hot water is required at more that one points (e.g, multi storied building)
this type is used. It holds water of high pressure, (more than 300 psi) it is called pressure type.
The construction of this type is shown in Fig.10.7
This type of heater gets its cold water
supply through a cistern which is connected
to the water main and supply to it is
controlled automatically with the help of a
float value as shown in fig. Similar to Non-
pressure type, this also contains inner and
outer tank separated by glass wool which
prevents heat transfer from inner tank to
outer tank. The other parts are inlet pipe,
outlet pipe, heating element, thermostat,
vent pipe (similar to a pressure relief valve
in non pressure type) to control the water
pressure inside the tank and thus keeps the
tank form exploding. In this type, hot water
is collected at more that one service point.
So the outlet pipe is connected to various
service points through control valves.
Working : The working principle of this type is same as that of non-pressure type except that
the cold water supply and hence the pressure is controlled automatically with the help of float
value. This heater is used to supply hot water to different floors of the building. In this, source
point (location of heater) and access point (service point) are at different places. So the users
have no control on the cold water in. Therefore, cold water will get in continuously and get mixed
with hot water. So when hot water is disposed regularly, the heat in the water gets decreased.
Fig. 10.7 - Pressure type storage water heater