steam-heating coil is located. Here the water is heated
and begins to circulate. Eventually, all of the water in
the tank becomes heated. When hot water is drawn,
more cold water enters the tank and this heating process
repeats itself. This action maintains a full tank of hot
water for use whenever hot water is needed. According
to safety regulations, the hot water should not exceed
180°F. The storage type of water heater may be
constructed to be installed in either the horizontal or the
Tappings are usually provided in the tank for a
thermometer a thermostatic element for a
temperature-regulating valve (which will be discussed
later in this chapter) and a safety valve. The tube coil
should be inspected annually to make sure steam is not
leaking into the water. The chemicals that are
sometimes used in the steam may make the people who
use the water sick if they drink it.
Instantaneous heaters are used primarily as boiler
feedwater heaters; however, they are sometimes used to
provide potable (drinking) water at some installations.
The operation of the instantaneous-type heater is
basically the same as the storage-type heater; their
construction, however, is quite different. The diameter
of the instantaneous heater is small in comparison to the
storage-type heater. The outer shell of the instantaneous
heater is small in comparison to the storage-type heater.
The outer shell of the instantaneous heater barely covers
the tube coil, as you can see in figure 3-21. In some
makes, the water is circulated through the coil, and the
steam is released in the shell and surrounds the coil. A
temperature-regulating valve controls the water
temperature for both types of heaters.
The temperature regulator is used to regulate the
quantity of steam necessary to maintain the hot water at
Figure 3-21.The instantaneous-type water heater.
the desired temperature. The unit consists of a
temperature bulb, copper line, diaphragm, spring and
temperature adjustment, and steam valve. A typical
temperature-regulating valve is shown in figure 3-22.
The bulb and copper tube are called the capsule and
capillary tube. They contain a gas that expands or
contracts with a change in temperature. The capillary
tube is connected to the top of the temperature regulator
which contains a diaphragm (bellows). The diaphragm
(bellows) is connected to the valve stem. A spring holds
the valve open at low temperatures. When the
temperature rises in the water tank, the gas in the
temperature bulb expands and forces the diaphragm
down, closing the steam valve. Adjusting the tension of
the spring can control the water temperature. A steam
trap in the steam-heating system returns the condensed
steam to the condensate tank.
The hot-water tank accessories consist of a
temperature gauge that has a range of 40°F to 210°F and
a safety valve or pressure relief valve. The relief valve is
set at a pressure that is 10 pounds higher than the
operating pressure, and both the setting and the valve
must comply with current ASME code specifications.
CONDENSATE RETURN PUMP
Condensate return pumps cause the water that has
condensed from the steam in radiators, heating coils,
convectors, and unit heaters to circulate back to the
boiler. One type of condensation return pump is shown
Figure 3-22.A typical temperature-regulating valve.