Theory Of Operation - CAIRE Liberator G4 Series Technical & Service Manual

VI

Theory of Operation

Filling
The Liberator is filled by connecting a pre-purged transfer line
with a fill adapter from a larger liquid oxygen source to the
Liberator side fill or top fill QDV. The Liberator vent valve is
then opened. The pressure differential between the Liberator and
source tank forces liquid oxygen through the transfer line and
into the Liberator inner vessel.
There will be some oxygen vaporized during filling. This gas is
discharged through the vent valve. When the Liberator is full, liq-
uid oxygen is expelled. Disconnecting the fill adapter from the
Liberator QDV and closing the Liberator vent valve terminates
the fill process.
FIGURE 2: Filling
Vent Valve
Gas
Saturation Pressure
The saturation point of a liquid is a steady-state condition where
the liquid has absorbed the maximum amount of heat possible.
A liquid can be at its saturation point at a number of different
pressures and temperatures, but each specific saturation pressure
has a corresponding saturation temperature and vice-versa (see
Figure 3). This means that the final temperature of your liquid
oxygen is dependent upon the pressure at which it is transferred
from the storage system to the Liberator. For the purposes of this
manual, we will speak in terms of saturation pressure, since it is
easier to control than temperature. Treat saturation temperature
as a dependent variable of saturation pressure.
Liquid
Fill Connection
(QDV)
Gas
FIGURE 3: Temperature vs. Saturation Pressure
-155
-160
-165
-170
-175
1.4, -173.8
-180
0.0, -183.0
-185
-190
0 1 2 3
SATURATION PRESSURE (BAR)
There are two conditions which can seriously affect the overall
efficiency and operation of the system:
1. Saturation pressure of the liquid oxygen in the fill source is
substantially higher than the Liberator operating pressure
(oversaturated).
2. Saturation pressure of the liquid oxygen in the fill source is
substantially lower than the Liberator operating pressure (un-
dersaturated).
For example, when a Liberator is filled from a liquid source satu-
rated at 6,9 bar (100 psig), larger transfer losses will occur. This is
because the Liberator is designed to operate at 1,4 bar (20 psig),
and the liquid it is filled with is saturated at a much higher pres-
sure and at its correspondingly higher temperature. It is neces-
sary for this liquid to reach equilibrium at a lower pressure and
temperature before the relief valve will close and the Liberator
will operate properly.
In order to become saturated at 1,4 bar (20 psig), the liquid oxy-
gen must release enough heat for its temperature to be lowered to
the temperature corresponding to a pressure of 1,4 bar (20 psig),
as shown in the graph. The temperature is lowered through boil-
ing. All of the gas generated by this boiling is vented through the
relief valve and/or primary relief valve and is lost.
If the saturation pressure of the liquid oxygen in the filling ves-
sel is lower than the normal operating pressure of the Liberator,
oxygen vaporization within the dewar works to raise the system
pressure to the required 1,4 bar (20 psig). This may require as
long as a day. The time required for saturation to 1,4 bar (20 psig)
depends on the initial liquid saturation pressure.
Liberators Technical Service Manual • PN 13350704 Rev K
6.9, -157.4
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