a) Full flow of heated water through tank, which requires
b) Inflexibility of expansion vessel location, which can require
a) Relatively cool expansion vessel expansion tank which is
not enter the tank.
Flexibility in locating expansion vessel.
c) System pressure that can be designed for any value within
a) Higher system pressures. In order to ensure that system
pressure will not drop below saturation pressure, a safety factor must be
included in design considerations. This may necessitate the use of higher
pressure rated fittings and valves.
Inert gas costs.
Expansion Vessels. All systems should have dual expansion tanks to
allow for inspection and maintenance while the system is on-line.
Purpose. Expansion vessels absorb the expansion and contraction of
system water due to load variation and ensure, at all times, a controlled
system pressure above that corresponding to the saturation temperature. They
may also act as a momentary source of water supply in case of a system
Sizing. Under no circumstances where heating is the basic load
should the expansion volume be based on cold water conditions. The expansion
volume should be based on normal design supply and return line differentials.
In a steam-pressurized system the diameter of the expansion vessel should be 6
ft (1.83 m) or more with an aspect ratio of 3.5 to 1.
Expansion Vessel Volume for Steam Pressurized Systems.