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Quick Reference Guide - Page 10
Checking water volume and initial pressure of expansion vessel
The expansion vessel of the Hydro Unit has a capacity of 12 litres.
The initial pressure of the expansion vessel is 0.1 MPa (1 bar).
The suggested initial water charge is 0.2MPa (2 bar).
The pressure of the safety valve is 0.3 MPa (3 bar).
Verify whether the capacity of the expansion vessel is sufficient using the following expression. If
the volume is insufficient, install an appropriate external expansion vessel.
V Action
< 12 L Internal Expansion Vessel Size OK
> 12 L
Internal Expansion Vessel Size too small.
Install appropriate external expansion vessel
V: Necessary total vessel capacity (L)
Ɛ: Water expansion coefficient at average hot water temperature
Vs: Total water volume in the closed system (Do not include Hot Water Cylinder)
P1: System pressure at tank setting position (Mpa_abs*).
(Pipe inner pressure during pump operation before heating device operates = water supply
pressure)
P2: Maximum pressure used during operation at tank setting position (MPa_abs*).
(= safety valve setting pressure)
* The absolute pressure value (abs.) is obtained by adding the atmospheric pressure (0.1 MPa (1
bar)) to the gauge pressure.
Water temperature and expansion coefficient (Ɛ)
Water temperature and expansion coefficient (Ɛ)
Hot water temperature
(°C)
Expansion rate
(Ɛ)
Hot water temperature
(°C)
Expansion rate
(Ɛ)
0 0.0002 50 0.0121
4 0.0000 55 0.0145
5 0.0000 60 0.0171
10 0.0003 65 0.0198
15 0.0008 70 0.0229
20 0.0017 75 0.0258
25 0.0029 80 0.0292
30 0.0043 85 0.0324
35 0.0050 90 0.0961
40 0.0078 95 0.0967
45 0.0100 - -
Example
Maximum Hot Water temperature: 55°C, initial
water charge: 0.2MPa and system volume: 200 L.
The calculated Vessel capacity (V) is 11.6 L:-
0.0145
x
200
(0.2+0.1)
(0.3+0.1)
11.6
=
1
-
In this case V < 12 L therefore the internal
expansion vessel is sufficient.
There is no need to install an external expansion
vessel.