The glass or porcelain lined tank is the most widely used. (Figure 2-25) It is
available in stock standard sizes from a few gallons to 120 gallons. Larger sizes, up
to thousands of gallons, can be constructed on a custom-made basis. In many
cases it is more cost-effective to use two or more "standard" tanks rather than one
large "custom" one. Many manufacturers offer tanks with internal coils.
A lining is necessary, because a large amount of oxygen is dissolved in the storage
water. In DHW systems, new water, with new supplies of dissolved oxygen, is
introduced every day. This dissolved oxygen makes the water corrosive to
Other water conditions increase its corrosiveness. In some areas, the pH of the
water is low. This acidic condition accelerates corrosion. Sometimes the amount of
dissolved solids in the water is high, which also increases the problem.
If any gaps in the glass lining exist, the water will attack the bare steel. In a matter
of months, a leak will occur, even in areas with "good" water.
2.7 COMPONENT OPERATION