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 180F. The storage type of water heater may be constructed to be installed in either the horizontal or the vertical position.
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 40F to 210F 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 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.Continue Reading