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For example, assuming a system containing a 20% concen-
tration of ethylene glycol and 50 feet (15.2 m) in height from
the top of the system to the expansion tank, the minimum tank
pre-charge pressure would be:
Tank Pressure = 4 + (50 / 2.38) = 25.0 psig
= 27.6 + (15.2 x 22.6 / 2.38) = 171.9 kPa
Table 2 — “X” Factor for Setting Tank Pressure
NOTE: If expansion tanks are placed elsewhere in the system this
method cannot be used since extra pressure drop between the tank
and the pump must be accounted for.
NOTE: If the system requires a pre-charge greater than
40 psig (276 kPa), increase pressure as described below.
Expansion Tank Pre-Charge
— To pre-charge the expansion
tank, do the following steps:
1. Check the tank air pressure at the pre-charge connection
with an accurate pressure gage. Adjust as needed.
2. If additional pressure is required, charge the tank with oil-
free compressed air or nitrogen gas. Occasionally check
the pressure as when filling a tire.
3. Check the air valve for leakage. If it leaks, relieve the
pressure and replace the core with a Schrader type tire
core. DO NOT depend on the valve cap to seal the leak.
Once the system is pressurized, the pressure at the connec-
tion point of the expansion tank to water piping will not change
unless the water loop volume changes (either due to addition/
subtraction of water or temperature expansion/contraction).
The pressure at this point remains the same regardless of
whether or not the pump is running.
Since the expansion tank acts as a reference point for the
pump, there cannot be two reference points (two expansion
tanks) in a system (unless manifolded together). If system
volume or other design considerations warrant the placement
of another expansion tank somewhere in the system, the expan-
sion tank in the 30RAP hydronic package MUST be discon-
nected from its hose and the end of the hose securely plugged.
This is also true for applications where two or more 30RAP
chillers are placed in parallel. There should not be more than
one expansion tank in the system (unless manifolded together
as seen in Fig. 12). The expansion tanks must be disconnected
from the 30RAP hydronic package. It is permissible to install
the expansion tank(s) in a portion of the return water line that is
common to all pumps, providing that the tank is properly sized
for combined system volume.
If the application involves two or more chillers in a primary/
secondary system, a common place for mounting the
expansion tank is in the chilled water return line, just before the
decoupler. See Fig. 13 for placement of expansion tank in
primary/secondary systems.
The expansion tank included in the 30RAP hydronic pack-
age is a diaphragm tank, meaning that a flexible diaphragm
physically separates the water/air interface. With this type of
expansion tank, it is undesirable to have any air in the water
loop. See the section on air separation below for instructions on
providing air separation equipment.
AIR SEPARATION — For proper system operation, it is
essential that water loops be installed with proper means to
manage air in the system. Free air in the system can cause
noise, reduce terminal output, stop flow, or even cause pump
failure due to pump cavitation. For closed systems, equipment
should be provided to eliminate all air from the system.
The amount of air that water can hold in solution depends
on the pressure and temperature of the water/air mixture. Air is
less soluble at higher temperatures and at lower pressures.
Therefore, separation can best be done at the point of highest
water temperature and lowest pressure. Typically, this point
would be on the suction side of the pump as the water is return-
ing from the system or terminals. Generally speaking, this is
the best place to install an air separator, if possible.
1. Install automatic air vents at all high points in the system.
(If the 30RAP unit is located at the high point of the
system, a vent can be installed on the piping entering the
heat exchanger on the ¼-in. NPT female port.)
2. Install an air separator in the water loop, at the place
where the water is at higher temperatures and lower
pressures — usually in the chilled water return piping.
On a primary-secondary system, the highest temperature
water is normally in the secondary loop, close to the
decoupler. Preference should be given to that point on the
system (see Fig. 13). In-line or centrifugal air separators
are readily available in the field.
It may not be possible to install air separators at the place of
lowest pressure and highest temperature. In such cases, prefer-
ence should be given to the points of highest temperature. It is
important that pipe be sized correctly so that free air can be
moved to the point of separation. Generally, a water velocity of
at least 2 feet per second will keep free air entrained and
prevent it from forming air pockets.
Automatic vents should be installed at all physically elevat-
ed points in the system so that air can be eliminated during
system operation. Provision should also be made for manual
venting during the water loop fill. It is important that the
automatic vents be located in accessible locations for
% GLYCOL
ETHYLENE
GLYCOL
PROPYLENE
GLYCOL
0 (pure water) 2.31 2.31
10 2.36 2.33
20 2.38 2.36
30 2.40 2.38
40 2.43 2.38
50 2.47 2.40
1
2
6
5
3
4
7
(HIDDEN)
LEGEND
1—Strainer
2—Blow-Down Valve
3—Discharge Check Valve
(Dual Pumps Only)
4—Balancing Valve with
Drain Plug
5—Field Connections
6—Heater
7—Service Valves
Fig. 12 — Typical Dual Pump Package
a30-4635