Specifications

18
EXPANSION OR AIR CUSHION TANK
It is necessary to make provision for the increased
volume of water in the boiler and heating system caused
by thermal expansion. This is accomplished by
installing an expansion tank. The tank is usually located
above the boiler with a piping connection between the
bottom of the tank and the top of the boiler.
When the boiler and system is initially filled with water,
a pocket or cushion of air is trapped within the tank.
This air cushion provides the additional space required
to accommodate the increased volume of water caused
by thermal expansion. The use of an expansion tank
permits operation through all ranges of boiler water
temperature, including temperatures above 212ºF
without opening the safety-relief valve.
1. If the boiler is used for space heating, the heating
system water volume must be added to the boiler
water volume in order to determine the expansion
tank requirements.
2. Before selecting expansion tank, consult local
authorities to determine ASME or State
requirements.
3. There are occasions in operation when the expansion
tank becomes “waterlogged” or filled with water.
When this occurs, it is necessary to close the stop
valve to the boiler and open the draw valve on the
tank. When the water is completely drained and the
tank is again filled with air, close the drain valve and
open the valve to the boiler.
4. It may be more economical to use the pressurized air
cushion tank rather than the conventional type
expansion tank listed above. When selecting a
pressurized air cushion tank, consult your dealer.
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