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SECTION B - EXPANSION TANKS
Why do I need an expansion tank?
Heated from 10 to 60ºC, water expands in volume by about 2%. The calorifier expands too, but
not as much as the water. A litre or more of hot water may need to escape from your calorifier
as it heats up.
A normal accumulator
tank can absorb this
excess water, provided it
is of sufficient size. In the
process, hot water will
flow back into the cold
water line. If hot water
back-flow cannot be
tolerated, a non-return
valve may be fitted in the
inlet line to the calorifier.
The expansion water will
then be discharged
through the calorifier
temperature / pressure
relief valve, which opens
at the maximum working
pressure of the calorifier.
To avoid water wastage,
to prevent unnecessary stress on the calorifier, and to avoid build-up of deposits in the relief
valve, an additional expansion tank may be fitted in the inlet line to the calorifier (see diagram).
What size of expansion tank do I need?
The required capacity of the expansion tank depends on:
-
pump cut-out pressure
-
the difference between the pump cut-out pressure and the opening pressure of
the relief valve in the calorifier
-
the volume of stored water in the calorifier
All three of these factors are taken into account by the EXPANSION TANK VOLUME FACTOR,
shown in the table below.
To calculate the expansion tank volume you require, proceed as follows:
Pressure relief valve setting ►
Pump cut-out pressure ▼
1.0 bar (15psi)
1.4 bar (21psi)
1.8 bar (25psi)
2.0 bar (29psi)
2.8 bar (40psi)
EXPANSION TANK VOLUME FACTOR
2.5 bar
(37psi)
22
16
10
7
n/a
3 bar
3.5 bar
(44psi)
(51psi)
24
28
20
24
15
18
12
16
n/a
8
5 bar
(74psi)
34
30
26
25
18
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