Toyotomi OM-128HH Installation Manual page 9

Selecting an Expansion Tank
Select an expansion tank by referring to the following calculation formula and the calculation formulas pro-
vided by the manufacturers of tanks sold commercially.
Expansion Tank Calculation Formula
P +14.5
2
V = + 1.1 V
0
P -P
2 1
(gal) = Water heater's heat exchanger volume + convector capacity + piping holding capacity (See the table below).
V
o
Water holding
Nominal diameter (in.)
capacity per
foot of copper
Holding capacity (gal/ft)
pipe.
Water holding
Nominal diameter (in.)
capacity per
foot of tap
Holding capacity (gal/ft)
water line.
Expansion
coefficient of
Coefficient of Expansion
Water
Supplying water to and releasing air from the heating piping.
1. When supplying water to the heating piping, close the valve 1,
then open the heating piping's drain valve and supply valve and
fill the piping with water.
Let the supply water pressure be lower than the set pressure on
the pressure relief valve.
2. Close the drain valve when circulating water starts to come out
of the drain outlet, then open the air release valve in the heating
piping and release the air out of the piping.
3. Open the valve 1 and run the circulation pumps, circulating water through the piping while releasing
the air out. The air will be efficiently released from the pipes if the air is released from the heating piping
once with each circuit of the water in the piping.
4. After circulating water through the piping for approximately 10 minutes, close the supply water valve,
then close the air release valve.
:
V Tank Capacity of Expansion Tank (gal)
:
Vo Total volume of heating piping system (gal)
:
Expansion coefficient of water
:
P1 Expansion tank's gas charge pressure (PSI)
Set a gas charge pressure that is the maximum static pressure brought to
bear on the expansion tank (the pressure drop between the expansion tank
and the convector) with 1.45~2.9 PSI added.
:
P2 Pressure Relief Valve Set Pressure (PSI)
1/4
0.0040
1/2
0.0161
Temperature 176˚F (80˚C)
0.0291
3/8 1/2 3/4
0.0083 0.0133 0.0269
3/4 1 1-1/4
0.0298 0.0483 0.0886
Water
Heater
Side
Supply
Water
Valve
1 1-1/4 1-1/2
0.0455 0.0680 0.0953
1-1/2
0.1095
Valve 1
Convertor
Drain
Valve
8