CAIRE Liberator G4 Series, Liberator 30, Liberator 20, Liberator 37, Liberator 45 Technical & Service Manual

Liberators —G4

Technical Service Manual

1

Liberators

SERVICE MANUAL

LIBERATOR SERIES—G4

LIB20, LIB30, LIB37, LIB45, LIB60

CAIRE, Inc.
2200 Airport Industrial Dr., Ste. 500
Ball Ground, GA 30107

www.cairemedical.com

Customer/Technical Service:
North and South America

Phone (US Only): 800-482-2473 Fax: [phone]

US: 770-721-7759 Fax: [phone]
Asia, Australia, Pacific Rim
Phone: [phone] Fax: [phone]
Europe

Phone: [phone] Fax: [phone]

Preface

I

For Customer or Technical Service needs (product assistance, ordering, part numbers, specifications, unexpected events, etc.) contact:

CAIRE Inc.

2200 Airport Industrial Dr., Ste. 500

1-800-482-2473

www.cairemedical.com

www.heliosoxygen.com

Disclaimer

This manual is intended for use by experienced personnel only. No attempt should be made to fill or maintain this equipment
until both this manual and the Patient Operating Instruction booklet have been read and fully understood.

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Liberators

Abbreviations

FCV Flow Control Valve PRV Primary Relief Valve

LED Light Emitting Diode QDV Quick Disconnect Valve
LOX Liquid Oxygen RMA Return Materials Authorization
LPM Liters Per Minute RP Repair Procedure
NER Normal Evaporation Rate RR Removal and Replacement

POI Patient Operating Instructions SRV Secondary Relief Valve

N2 Nitrogen Gas O2 Oxygen Gas

TF Top Fill SF Side Fill

DF Dual Fill PTFE Polytetrafluoroethylene (“Teflon”)

DISS Diameter Index Safety System

Definition of Terms

WARNING Description of a condition that can result in personal injury or death.
CAUTION Description of a condition that can result in equipment or component damage.

NOTE A statement containing information important enough to emphasize or repeat.
(ITEM) Item numbers used throughout this manual are shown on the illustrations beginning on page 34.

Definition of Product Symbols

Table 1: Definition of Product Symbols

Symbol Definition Symbol Definition

Reservoir Full Do not smoke near unit

Keep unit well ventilated at all
times

Read user manual before opera­tion. See user manual for instruc­tions

IP21

Reservoir Empty

Portable Full Do not touch frosted parts

Portable Empty Keep unit in upright position

Low Battery (9VDC) CE Mark

Classification according to the de­gree of protection against ingress
of water.

Type BF (Electrical Safety)

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Liberators

Table of Contents

I. Preface ..............................................1

II. Table of Contents ....................................3

III. Equipment Description ...............................4

IV. Specifications ........................................5

V. Safety ................................................6

VI. Theory of Operation .................................11

VII. Unpacking and Setup ...............................14

VIII. Operation ...........................................15

II

IX. Maintenance ........................................17

X. Troubleshooting ....................................19

XI. Troubleshooting Charts .........................20–23

XII. Repair Procedures ...................................24

XIII. Service Tools/Equipment/Supplies ...................38

XIV. Parts Price List .......................................39

XV. Ordering Information ................................40

XVI. Return & Restocking Policy ..........................41

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Equipment Description

FIGURE 1: Liberator Components

1. Cryogenic Container – This assembly is a double walled,
vacuum insulated dewar for storing liquid oxygen (LOX) at
approximately -173°C (-280° F). The inner vessel is designed
to safely hold liquid oxygen and is protected from over pres­surization by the primary relief valve. Vacuum insulation
between the inner and outer vessel keeps outside heat from
causing the cold liquid inside to evaporate.

2. Breathing Circuit – This circuit consists of the manifold as-
sembly, fixed orifice rotary flow control valve (FCV), breath­ing coil, and warming coil. It withdraws liquid oxygen from

ryogenic container, warms it to near ambient tempera-

the c
ture, and regulates the flow of oxygen gas to the patient. Any
water that condenses on the cold coils is routed into the con­densate bottle. An economizer regulator is utilized to con­serve LOX by drawing oxygen head gas into the breathing
circuit.

3. Shroud Assembly – The shroud assembly houses and pro-
tects the breathing circuit and liquid level meter. Labels list­ing safety information and patient operating instructions are
affixed to the side of the shroud.

* For Top Fill or Dual Models Only

The CAIRE Liberator® is the stationary component of the
Liberator/Portable supplementary oxygen system. The Liberator
incorporates a stainless steel cryogenic container with the valves,
plumbing, and associated hardware required to deliver gaseous
oxygen to the patient at near ambient temperature.
The Liberator is comprised of four major assemblies, grouped
according to function.

4. Liquid Level Meter – This system uses a capacitance probe
and an electronic (LED) readout to measure and display the
LOX level by pressing the onboard operate button.

An optional roller base can be provided to help move

the Liberator.

Serial Number Information

For Liberators manufactured before 2006, the serial number
was ten digits. The first three digits represented CAIRE
specific information, followed by two digits signifying the
year of manufacture, followed by a two digit number to digit
number to signify the week of the year that the unit was
manufactured and ends with three digits signifying the unit's
production number for that week.

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Specifications

MODEL LIBERATOR 20 LIBERATOR 30 LIBERATOR 37 LIBERATOR 45 LIBERATOR 60

Volume of LOX
(typical)

Weight of LOX at 24
psig (166 kPa) Satura­tion (typical)

Gasous Oxygen
Equivalent @ 1atm
and 70F

Height

Diameter

Empty Weight

Full Weight

Outlet Pressure

Nominal Operating /
Economizer Pressure

Density (Weight of
LOX) @ Nominal Op­erating/Economizer
Pressure

Primary Relief Valve
Opening Pressure

Primary Relief Valve
Reseat Pressure

Secondary Relief
Valve Opening
Pressure

Secondary Relief
Valve Reseat Pressure

Normal Evaporation
Rate (NER - typical)

Maximum Outlet
Flow

Contents Indicator

Operating Tempera­ture

Storage Temperature

21.0 liters / .021 m3 31.0 liters / .031 m3 37.3 liters / .0373 m3 45.7 liters / .0457 m3 60.2 liters / .0602 m3

23kg (50.7 lbs) 33.9 kg (74.8 lbs) 40.8 kg (90 lbs) 50.04 kg (110.3 lbs) 65.9 kg (145.3 lbs)

17,337 liters / 612 ft3 25,580 liters / 903 ft3 31,121 liters / 1099 ft3 37,724 liters / 1332 ft3 49,679 liters / 1754 ft3

62.2 cm / 24.5 in 74.9 cm / 29.5 in 83.2 cm / 32.75 in 94.0 cm / 37 in 99.1 cm / 39 in

35.6 cm / 14 in 35.6 cm / 14 in 35.6 cm / 14 in 35.6 cm / 14 in 40.6 cm / 16 in

17.69 kg / 39 lbs 22.04 kg / 48.6lbs

40.69 kg / 89.7 lbs 55.94 kg / 122.32 lbs 63.48 kg / 140 lbs 74.99 kg / 165.32 lbs 100.1 kg / 220.68 lbs

1.4 bar / 20 psi 1.4 bar / 20 psi 1.4 bar / 20 psi 1.4 bar / 20 psi 1.4 bar / 20 psi

1.4 bar / 20 psi 1.4 bar / 20 psi 1.4 bar / 20 psi 1.4 bar / 20 psi 1.4 bar / 20 psi

1.095 kg/L or

2.413 lbs/L

1.6 bar / 23.2 psi 1.6 bar / 23.2 psi 1.6 bar / 23.2 psi 1.6 bar / 23.2 psi 1.6 bar / 23.2 psi

1.4 bar / 20.5 psi 1.4 bar / 20.5 psi 1.4 bar / 20.5 psi 1.4 bar / 20.5 psi 1.4 bar / 20.5 psi

2.1 bar / 30.5 psi 2.1 bar / 30.5 psi 2.1 bar / 30.5 psi 2.1 bar / 30.5 psi 2.1 bar / 30.5 psi

1.9 bar / 27 psi 1.9 bar / 27 psi 1.9 bar / 27 psi 1.9 bar / 27 psi 1.9 bar / 27 psi

.73 kg / 1.6 lbs .73 kg / 1.6 lbs .73 kg / 1.6 lbs .73 kg / 1.6 lbs .73 kg / 1.6 lbs

15 L/min 15 L/min 15 L/min 15 L/min 15 L/min

Capacitance Probe
with LED Readout

10°C to 40°C 95%
max. relative humidity

-40°C to 70°C 95%
max. relative humidity

(Nominal Values)

LIBERATOR SPECIFICATIONS

22.68 kg / 50 lbs 24.95 kg / 55 lbs

1.095 kg/L or

2.413 lbs/L

Capacitance Probe
with LED Readout

10°C to 40°C 95%
max. relative humidity

-40°C to 70°C 95%
max. relative humidity

1.095 kg/L or

2.413 lbs/L

Capacitance Probe
with LED Readout

10°C to 40°C 95%
max. relative humidity

-40°C to 70°C 95%
max. relative humidity

1.095 kg/L or

2.413 lbs/L

Capacitance Probe
with LED Readout

10°C to 40°C 95%
max. relative humidity

-40°C to 70°C 95%
max. relative humidity

34.19 kg / 75.4 lbs

1.095 kg/L or

2.413 lbs/L

Capacitance Probe
with LED Readout

10°C to 40°C 95%
max. relative humidity

-40°C to 70°C 95%
max. relative humidity

Note:
All specifications are applicable for G4 Liberators only and based upon optimum environmental and
pressure conditions as stated above.

Listed capacities have incorporated a 2% ullage in compliance with ADR requirements.

At optimum operating conditions, the conversion factor of liquid oxygen to gaseous oxygen is 1:860.

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Safety

Oxygen, as it exists at standard atmospheric pressure and tempera­ture, is a colorless, odorless, and tasteless gas. Oxygen constitutes
21% of the atmosphere, by volume. Aside from its well-docu­mented ability to sustain life, oxygen also supports combustion,
even though it is nonflammable. Many substances which will burn
in air burn at a faster rate and at a higher temperature in an oxy­gen-enriched atmosphere. Other materials that do not burn in air
will burn as oxygen concentration increases. Additionally, many
greases and liquid solvents become extremely hazardous materi­als when placed in an oxygen-enriched environment. In its liquid
form, oxygen is still odorless and tasteless, but is pale blue in color.
At an operating pressure of 1,4 bar (20 psig), the temperature of
liquid oxygen is about -173°C (-280° F). Skin exposed to such a low
temperature can become severely frostbitten.

These hazards require certain safety precautions to be taken when
working with or around gaseous and/or liquid oxygen:

1. Never permit combustible substances such as greases, oils,
solvents, or other compounds not oxygen compatible to
contact any component of the unit exposed to higher-than­atmospheric concentrations of gaseous or liquid oxygen. This
especially applies to tubing, fittings, and valves.

2. Keep oxygen equipment away from open flames or electrical
appliances such as heaters, stoves, toasters, and other devices
with heating elements.

3. Never permit smoking in an area where oxygen equipment is
repaired, filled, or used.

WARNING: Excess accumulation of oxygen creates an oxygen­enriched atmosphere (defined by the Compressed Gas
Association as an oxygen concentration above 23%). In an
oxygen-enriched atmosphere, flammable items may burn
vigorously and may ex-plode. Certain items considered non­combustible in air may burn rapidly in such an environment.
Keep all organic materials and other flammable substances
away from possible contact with oxy-gen; particularly oil, grease,
kerosene, cloth, wood, paint, tar, coal dust, and dirt which may
contain oil or grease. DO NOT permit smoking or open flame
in any area where oxygen is stored, han-dled, or used. Failure
to comply with this warning may result in serious personal
injury.

WARNING: In the event a unit is dropped, tipped over, or unrea­sonably abused, immediately, but cautiously, raise the container
to its normal vertical position. If substantial container damage
has occurred, remove the liquid oxygen from the vessel in a safe
manner (RP23). Purge the unit with an inert gas (nitrogen) and
promptly return it to CAIRE for inspection. The container should
be prominently marked “CONTAINER DROPPED, INSPECT
FOR DAMAGE.” Failure to comply with these procedures may
result in personal injury and can seriously damage the container.

WARNING: Personnel must remove liquid oxygen and depres­surize the unit before removing parts or loosening fittings from
a unit. Failure to do so may result in personal injury from the
extreme cold of liquid oxygen and/or the pressure in the vessel.

4. Always wear goggles, a face shield, and insulated gloves when
working with or around liquid oxygen.

While CAIRE, Inc. equipment is designed and built to the most
rigid standards, no piece of mechanical equipment can ever be
made 100% foolproof. Strict compliance with proper safety prac­tices is necessary when using any Liberator unit. We recommend
that our distributors emphasize safety and safe handling practices
to their employees and customers. While safety features have been
designed into the unit and safe operations are anticipated, it is nec­essary that all distributor personnel carefully read and fully un­derstand WARNINGS, CAUTIONS, and NOTES throughout the
manual. Periodic review of this information is recommended.

CAUTION: The Liberator should be moved by utilizing the roller
base or hand truck. Do not roll units on their side or edge as in­sulation damage can occur. The Liberator must be used, stored,
and transported in a vertical position. Do not lay, store, or ship
the unit on its side.

WARNING: During transfer of liquid oxygen, components will
become extremely cold. Care should be used to avoid any contact
with these components, as serious frostbite may result.

WARNING: During transfer of liquid oxygen gas blowoff from
the vent valve creates a loud horn-like noise. Ear protection is
recommended.

WARNING: Keep filled unit upright at all times. Tip over of filled
unit may result in liquid oxygen leakage and/or an oxygen-en­riched atmosphere.

WARNING: Only use replacement equipment which is compat­ible with liquid oxygen and has been cleaned for oxygen use. Do
not use regulators, fittings, hoses, etc. which have been previously
used in non-oxygen service.

WARNING: This product can expose you to chemicals
including Nickel, which is known to the State of California to
cause cancer. For more information, go to
www.P65Warnings.ca.gov.

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Safety

WARNING: Medical electrical Equipment needs special precau-

tions regarding EMC and needs to be installed and put into service
according to the EMC information provided in this manual.

WARNING: Portable and mobile RF communications equipment
can affect Medical Electrical Equipment.

Table 1

Guidance and Manufacturer’s declaration—electromagnetic emissions

The Liberator is intended for use in the electromagnetic environment specified below. The customer or the user of the Liberator should
assure that it is used in such an environment.

Emissions test Compliance Electromagnetic environment—guidance

RF emissions Group 1 The Liberator uses RF energy only for internal function.
CISPR 11 Therefore, its RF emissions are very low and are not likely to

RF emissions CISPR 11 Class B
Harmonic emissions The Liberator is suitable for use in all establishments, including

IEC 61000-3-2 Not applicable domestic establishments and those directly connected to the public
Voltage fluctuations/ low-voltage power supply network that supplies buildings used for
flicker emissions Not applicable domestic purposes.

IEC 61000-3-3

WARNING: The use of Accessories, transducers, and cables other
than those specified by the manufacturer may result in increased
Emissions or decreased immunity of the Liberator.

WARNING: The Liberator should not be used adjacent to or
stacked with other equipment, and that if adjacent or stacked use
is necessary, the Liberator should be observed to verify normal op­eration in the configuration in which it will be used.

cause any interference in nearby electronic equipment.

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Safety

Table 2

Guidance and manufacturers declaration—electromagnetic immunity

The Liberator is intended for use in the electromagnetic environment specified below. The customer or the user of the Liberator should
assure that it is used in such an environment.

Immunity test IEC 60601 t Compliance level Electromagnetic environment—guidance

Electrostatic ±6 kV contact ±6 kV contact Floors should be wood, concrete or ceramic tile. If floors
discharge (ESD) ±8 kV air ±8 kV air are covered with synthetic material, the relative
IEC 61000-4-2 humidity should be at least 30%.*

Electrical fast ±2 kV for power Not applicable Not applicable

transient/burst supply lines DC powered device
IEC 610004-4 ±1 kV for Not applicable

input/output lines No data input/output lines

±1 kV line(s)
Surge to line(s) Not Applicable Not Applicable
IEC 61000-4-5 ±2 kV line(s) DC powered device

to earth

Voltage dips, <5% UT (>95% dip

short interruptions in UT) for 0,5 cycle

and voltage 40% UT (60% dip
variations on in UT) for 5 cycles Not Applicable Not Applicable
power supply 70% UT (30% dip DC powered device
input lines in UT) for 25 cycles
IEC 61000-4-11 <5% UT (>95% dip

in UT) for 5 sec
Power frequency 3 A/m 3 A/m Power frequency magnetic fields should be at levels
(50/60 Hz) characteristic of a typical location in a typical
magnetic field commercial or hospital environment.
IEC 61000-4-8

Note: UT is the a.c. mains voltage prior to application of the test level.

* This statement indicates that the required testing was performed in a controlled environment and the Liberators are found to be com­pliant with regulations.

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Table 4*

Guidance and manufacturers declaration—electromagnetic immunity

The Liberator is intended for use in the electromagnetic environment specified below. The customer or the user of the Liberator
should assure that it is used in such an environment.

Immunity test IEC 60601 test level Compliance level Electromagnetic environment—guidance

Conducted RF 3Vrms Not Applicable Portable and mobile RF communications equipment should
IEC 61000-4-6 150kHz to 80 MHz Battery powered be used no closer to any part of the Liberator, including

device cables, than the recommended separation distance

calculated from the equation applicable to the frequency
of the transmitter.

Recommended separation distance
d = 1.2 √P
d = 1.2 √P 80 MHz to 800 MHz
d = 2.3 √P 800 MHz to 2,5 GHz

where P is the maximum output power rating of the
Radiated RF 3 V/m 3 V/m transmitter in watts (W) according to the transmitter
IEC 61000-4-3 80 MHz to 2,5 GHz manufacturer and d is the recommended separation

distance in meters (m).

Field strengths from fixed RF transmitters, as determined

by an electromagnetic site surverya, should be less than

the compliance level in each frequency rangeb.

Interference may occur in the vicinity of equipment marked
with the following symbol:

NOTE 1 At 80 MHz and 800 MHz, the higher frequency range applies.

NOTE 2 These guidelines may not apply in all situations. Electromagnetic propagation is affected by absorption and reflection
from structures, objects and people.

a

Field strengths from fixed transmitters, such as base stations for radio (cellular/cordless) telephones and land mobile radios,
amateur radio, AM and FM radio broadcast and TV broadcast cannot be predicted theoretically with accuracy. To asses the elec­tromagnetic environment due to fixed RF transmitters, an electromagnetic site survey should be considered. If the measured field
strength in the location in which the Liberator is used exceeds the applicable RF compliance level above, the Liberator should be
observed to verify normal operation. If abnormal performance is observed, additional measures may be necessary, such as reori­enting or relocating the Liberator.

b

Over the frequency range 150 kHz to 80 MHz, field strengths should be less than 3 V/m.

* This table is included as a standard requirement for equipment which has been tested to specific test levels and over specific
frquency ranges and been found compliant with regulations.

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Table 6*

Recommended separation distances between portable and mobile

RF communications equipment and the Liberator

The Liberator is intended for use in an electromagnetic environment in which radiated RF disturbances are controlled. The customer
or the user of the Liberator can help prevent electromagnetic interference by maintaining a minimum distance between portable and
mobile RF communications equipment (transmitters) and the Liberator as recommended below, according to the maximum output
power of the communications equipment.

Rated maximum output Separation distance according to frequency of transmitter

power of transmitter m

W 150 kHz to 80 MHz 80 MHz and 800 MHz 800 MHz to 2,5 GHz

d=1.2√P d=1.2 √P d=2.3 √P

0,01 0.12 m 0.12 m 0.23 m

0,1 0.38 m 0.38 m 0.73 m

1 1.2 m 1.2 m 2.3 m

10 3.8 m 3.8 m 7.3 m

100 12 m 12 m 23 m
For transmitters rated at a maximum output power not listed above, the recommended separation distance (d) in meters (m) can be
estimated using the equation applicable to the frequency of the transmitter, where P is the maximum output power rating of the trans­mitter in watts (W) according to the transmitter manufacturer.

NOTE 1 at 80 MHz and 800 MHz, the separation distance for the higher frequency range applies.

NOTE 2 These guidelines may not apply in all situations. Electromagnetic propagation is affected by absorption and reflection from
structures, objects and people.

* This table is included as a standard requirement for equipment which has been tested to specific test levels and over specific frquency
ranges and been found compliant with regulations.

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LOX TEMPERATURE (°C)

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, liq­uid 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

Liquid

Gas

Fill Connection

(QDV)

Gas

FIGURE 3: Temperature vs. Saturation Pressure

-155

-160

-165

-170

-175

-180

0.0, -183.0

-185

-190

012345678

1.4, -173.8

SATURATION PRESSURE (BAR)

6.9, -157.4

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 (un­dersaturated).

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.

For example, when a Liberator is filled from a liquid source satu­rated 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 pres­sure and at its correspondingly higher temperature. It is neces­sary 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 oxy­gen 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 boil­ing. 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 ves­sel 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.

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E

E

Theory of Operation

WARNING: Low oxygen flow rates to the patient may result if the

Liberator is filled with under-saturated liquid oxygen.

WARNING: The vent valve orifice does not guarantee properly
saturated LOX. The filling source must be correctly saturated or
low/high saturation will occur in CAIRE reservoirs.

To minimize the effect of undersaturated liquid in the Liberator, a
fixed orifice has been installed in the outlet of the vent valve. This
orifice regulates the back pressure in the unit during the fill pro­cess, resulting in improved saturation pressures in the Liberator.

Operation

If the flow control valve and vent valve are closed with LOX in the
unit, then the pressure in the inner vessel will remain near the pri­mary relief valve setting of 1,5-1,7 bar/21.8-24.2 psig.

In the Liberator, as in all vacuum-insulated cryogenic
contain-ers, some liquid (oxygen in this case) is always
evaporating into a gas. The rate of generation of this gas, with
the flow control valve closed, is called the normal evaporation
rate (NER). This gas is lost through the primary relief valve.

When the flow control valve is at any setting other than off, and
the economizer valve is open (presure over 1,4 bar (20 psig), see
Figure 4), gaseous oxygen is forced from the head space in the
inner vessel, through the economizer valve, to the breathing coil.
This process conserves or “economizes” liquid oxygen by with­drawing the head gas first, instead of allowing it to escape through
the relief valve.

While flowing through the breathing coil, the cold gaseous oxy­gen is warmed to near-ambient temperature before being me­tered and dispensed by the flow control valve.

Whenever gas is removed from the space above the liquid oxy­gen (head space), the inner vessel internal pressure begins to
drop slightly. When the pressure drops to 1,4 bar (20 psig), the
economizer valve closes,(see Figure 5) forcing liquid oxygen up
the withdrawal tube and through the warming coil where it be­comes gas.

The gas then flows through the bypass tee to the breathing coil,
the flow control valve, and then the patient.

As the pressure in the container increases over 1,4 bar (20 psig),
the economizer valve opens, and the cycle repeats, maintaining
constant oxygen flow, at the selected flow rate, to the patient.

FIGURE 4:
Operation between 1,4 Bar (20 PSI) and 1,7 Bar (24.2 PSI)

Gas to Patient

Breathing

Coils

conomizer

(Open)

Gas

FIGURE 5:

Operation between 1,2 Bar (18PSI) and 1,4 Bar (20 PSI)

Gas to Patient

Breathing

Coils

Warming

conomizer

Coils

(Closed)

*Note: The operation
detailed in both
Figures 4 and 5 are
considered normal
operation.

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Theory of Operation

Liquid Level Measurement

Liberators are equipped with a unique liquid level measurement
system. This system measures the level of liquid oxygen inside the
unit with a capacitance probe and displays that liquid level on the
level meter’s LEDs.

The liquid level probe consists of two concentric stainless steel
cylinders extending inside the inner vessel. As the liquid oxygen
level rises, the capacitance of this assembly goes up. The level
meter then displays the liquid level in the cylinder based on a
calibration relating capacitance to fill level. The higher the liquid
level in the dewar, the more LEDs are activated, beginning at the
left most LED.

Electrical connection between the level meter and the probe is
made via a single conductor JST connector. This male plug is at­tached to its female counterpart extending from the probe, creat­ing a watertight connection. A single ground wire is connected
from the meter to a male spade terminal on the mounting bracket.

The meter is powered by an internal battery offering battery
life of 5 years or more at 30 cycles per day. The meter has a low
battery (LOW BATT) indicator which signals the need for bat­tery replacement. The meter battery is covered under a 2-year
limited warranty. If battery failure occurs within 2 years of the
Liberator shipment date, contact CAIRE, Inc. customer service
for a replacement meter. If the meter battery is no longer under
warranty, the CR2032 coin cell battery can be replaced (RP5).
Replacement batteries can be found at most hardware stores or
they can be ordered through CAIRE customer service.

FIGURE 6: Liquid Level Meter Circuit

JST Connector

The new level meter improves upon the previous meter by in­tegrating all components within its casing, simplifying removal
and replacement (RP4). Even more importantly, there is a much
improved calibration procedure that requires no additional tools
and a range of error reporting codes which can be read directly
from the LEDs to report calibration errors. These can be found
in the calibration procedure (RP7).

: Tampering with meter battery housing will void the

NOTE
bat

tery’s 2-year warranty.

Liberators Technical Service Manual • PN 13350704 Rev K

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