Liquid oxygen converters

Essex Cryogenics of Missouri CRU-87/U: troubleshooting and error codes

The ServiceForge knowledge base holds 44 documented symptoms for the Essex Cryogenics of Missouri CRU-87/U, with 68 ranked causes, 74 diagnostic checks with test points and expected values, and 0 error codes. Each symptom below shows its causes and the first check; the rest is one connection away. Connect ServiceForge to your AI

Symptoms

Converter will not fill patient safety

Filling operation cannot be initiated or completed

Ranked causes

1. Ice in filler valve or filler line obstructs LOX flow (common)
2. Filler line not properly purged prior to filling (common)
3. Converter not sub-cooled before filling (occasional)
4. Filling pressure too low (occasional)
5. Defective converter (rare)

5 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Container assembly not filling with liquid oxygen high voltage

Liquid oxygen does not flow from vent in solid stream during fill procedure; gaseous spurts interrupt flow or no LOX flows

Ranked causes

1. Servicing hose not fully purged before filling (common)
2. Servicing pressure below forty (40) PSIG (common)
3. Container assembly already 75% or more full (false fill condition) (occasional)

First check

Verify servicing hose is purged

Test point: oxygen tank trailer servicing hose outlet
Expected: liquid oxygen flows from hose

2 more checks with pass and fail actions, 3 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Converter does not fill in required time patient safety

Filling operation proceeds but takes longer than specified

Ranked causes

1. Filling pressure too low (common)
2. Converter not sub-cooled before filling (occasional)
3. Defective converter (rare)

3 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Converter will fill only partially with gas only emitted from vent patient safety

Liquid oxygen does not accumulate; only gas exits vent valve

Ranked causes

1. Converter not sub-cooled prior to filling (common)
2. Buildup, vent and filler valve defective or partially open (occasional)
3. Pressure relief valve open (occasional)

3 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Converter will not build up pressure patient safety

Converter fails to maintain or develop required pressure after filling

Ranked causes

1. System leakage (common)
2. Fill, buildup and vent valve partially open venting gas (occasional)
3. Pressure relief valve open (occasional)

3 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Insufficient oxygen delivery rate patient safety

Converter not delivering required oxygen flow to aircraft systems.

Ranked causes

1. LOX level too low in converter (common)
2. Heat exchanger blockage or malfunction (occasional)
3. Pressure regulator failure (occasional)

First check

Measure LOX level in converter

Test point: Converter sight glass or level indicator
Expected: Adequate LOX visible; converter should be near full capacity liters

2 more checks with pass and fail actions, 3 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Low or no converter pressure patient safety

Pressure gauge indicates below normal or zero pressure

Ranked causes

1. Converter empty, defective probe or quantity indicator (common)
2. System leakage (occasional)
3. Pressure relief valve open or out of adjustment (occasional)

3 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Calibration: Quantity indicator using TTU-62/E Tester

Calibrate oxygen quantity indicator using TTU-62/E Tester capacitance measurement at empty and full states

Ranked causes

1. Quantity indicator requires calibration via capacitance tester (occasional)
2. Battery power or indicator failure (rare)

First check

Connect tester to converter probes and verify reading within limits

Test point: Converter probes
Expected: Within limits in T.O. 15X-1-1 Section VIII Figure 8-4 (10 Liter Capacitance Chart)

2 more checks with pass and fail actions, 3 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Converter fails to reach operating pressure after filling

Pressure closing valve not building pressure to nominal 75 psig after refill operation.

Ranked causes

1. Pressure closing valve bellows leak (occasional)
2. Buildup coil obstruction or leak (rare)

First check

Measure buildup time after filling

Test point: Converter outlet pressure gauge
Expected: Pressure reaches 75 psig within 5 minutes of fill completion, ±5 psig
Tools: Pressure gauge

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Converter pressure exceeds safe limits high voltage

Relief valve does not function; internal pressure could exceed 12,000 psig if demand not placed on converter, creating hazardous overpressure situation.

Ranked causes

1. Relief valve failed or not set correctly (unknown)
2. Pressure closing valve malfunction (unknown)

First check

Verify relief valve setting

Test point: Relief valve outlet
Expected: Pressure relief occurs at approximately 110 psig, ±10 psig

1 more check with pass and fail actions, 2 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Excessive pressure in servicing hose during fill high voltage

Pressure buildup in oxygen tank trailer servicing hose during filling operation

Ranked causes

1. Servicing hose not fully depressurized before disconnecting (common)
2. Pressure relief valve not opened or not equipped (occasional)

First check

Close servicing line shutoff valve

Test point: oxygen tank trailer servicing line shutoff valve (V-3)
Expected: valve fully closed

2 more checks with pass and fail actions, 2 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Excessive time to drain liquid oxygen from container assembly caution

Drain cycle takes longer than expected 3-hour baseline for 10-liter capacity with three valves at maximum flow

Ranked causes

1. Flow control valves not set to maximum flow rate during drain (common)
2. One or more flow control valves delivering below rated capacity (occasional)

First check

Verify each flow control valve set to maximum position

Test point: Flow control valve handle position
Expected: All three valves at maximum 15 LPM position

1 more check with pass and fail actions, 2 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Liquid oxygen leakage from container assembly patient safety

LOX escaping from outlet receptacles, fill port, or supply hoses during operation or storage

Ranked causes

1. Supply hose not properly connected to container assembly outlet receptacle (common)
2. Flow control valve not set to zero position before disconnecting supply hoses (occasional)

First check

Inspect LOX fill port for condition and function

Test point: LOX fill port
Expected: General good condition, smooth and positive action, freedom from all contamination, dust cover in place

1 more check with pass and fail actions, 2 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Quantity Indicator indicates empty patient safety

Indicator displays empty reading when converter contains liquid

Ranked causes

1. Dead batteries (common)
2. Converter empty, defective probe or quantity indicator (occasional)

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Quantity Indicator no reading patient safety

Indicator display is blank or unresponsive

Ranked causes

1. Dead batteries (common)
2. Converter empty, defective probe or quantity indicator (occasional)

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Calibration: Oxygen pressure relief valve high voltage

Test and calibrate Type V oxygen pressure relief valve with operating range 120-140 PSIG

Ranked causes

1. Pressure relief valve requires calibration per manual procedure (occasional)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Calibration: Pressure regulator high voltage

Set master pressure gauge to 50 PSIG with prescribed oxygen flow (45 LPM total) before operation

Ranked causes

1. Pressure regulator requires calibration per procedure (common)

First check

Verify pressure indication has stabilized on master pressure gauge

Test point: Master pressure gauge
Expected: Stabilized reading

1 more check with pass and fail actions, 1 corrective action, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Calibration: Quantity indicator using weight method

Calibrate oxygen quantity indicator by measuring indicator reading against actual liquid oxygen weight in five 2-liter increments

Ranked causes

1. Quantity indicator requires calibration verification (common)

First check

Ensure all LOX drained and indicator registers zero

Test point: Quantity indicator with OPERATE switch
Expected: Zero reading

3 more checks with pass and fail actions, 1 corrective action, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Container assembly lacks positive nitrogen pressure

Pressure gauge does not register a reading after shipment

Ranked causes

1. Nitrogen pressure lost during shipment (occasional)

First check

Verify pressure gauge reading on arrival

Test point: Pressure gauge
Expected: Positive pressure of gaseous nitrogen

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Container assembly leakage test high voltage

Pneumatic pressure test to verify all fittings and connections are leak-free

Ranked causes

1. Leakage test required for container integrity verification (common)

First check

Remove front panel assembly

Test point: Container assembly front
Expected: Panel fully removed

9 more checks with pass and fail actions, 1 corrective action, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Container assembly pressure below 45 PSIG

Pressure gauge reading indicates pressure lower than minimum safe operating pressure during operation or standby

Ranked causes

1. Insufficient pressure in container assembly (unknown)

First check

Check container assembly pressure gauge for proper operating pressure

Test point: Pressure gauge on top surface of container assembly
Expected: 50+5 psi, +/-5 psi

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Container assembly temperature unstable after filling caution

Container assembly temperature has not stabilized after liquid oxygen fill operation before transport or loading

Ranked causes

1. Insufficient stabilization time after filling (common)

First check

Wait for stabilization period

Test point: container assembly
Expected: thirty (30) minutes elapsed since fill completion

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Converter purging procedure high voltage

Procedure to purge converter assembly using heated nitrogen/air followed by cold oxygen purge to remove contaminants and moisture before use

Ranked causes

1. Converter requires purging prior to operation (common)

First check

Ascertain converter assembly is completely drained and empty

Test point: Converter assembly
Expected: Empty with no residual liquid oxygen

5 more checks with pass and fail actions, 2 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Filler line cannot be disconnected from filler valve caution

Filler line assembly stuck or frozen to valve connection

Ranked causes

1. Filler nozzle frozen to filler valve (common)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Flow control valve delivers incorrect flow rate patient safety

Rotameter reading does not match expected flow tolerance at a given valve position setting during verification test

Ranked causes

1. Flow control valve out of specification (unknown)

First check

Verify flow control valve flow rate at each position

Test point: Rotameter outlet of flow control valve
Expected: Position 0: No leakage; Position 2: 2.0±0.35 SLPM; Position 4: 4.0±0.59 SLPM; Position 6: 6.0±0.88 SLPM; Position 8: 8.0±1.17 SLPM; Position 10: 10.0±1.47 SLPM; Position 12: 12.0±1.77 SLPM; Position 15: 15.0±2.21 SLPM PSIG, ±5 PSIG
Tools: Rotameter (0-20 LPM), master pressure gauge (0-100 psig), tee fitting, tubing

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Frost collects on entire outer jacket of converter caution

Visible frost or ice accumulation on external converter surface

Ranked causes

1. Heat loss due to annular space leakage (common)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Incorrect flow control valve connection patient safety

Reverse connection of inlet/outlet fittings or non-compliant gas source may cause inaccurate oxygen flow rates and patient injury

Ranked causes

1. Incorrect fitting connection or non-standard gas pressure (common)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Liquid oxygen proximity to combustible materials caution

Equipment operated near absorbent materials, loose clothing, rags, gasoline, kerosene, oil, grease or other hydrocarbons, creating fire or spontaneous ignition hazard.

Ranked causes

1. Equipment located near combustible materials or hydrocarbons (occasional)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Liquid oxygen quantity indicator battery test reading outside acceptable range

Activation of test switch on quantity indicator does not display reading between 10.00 and 19.99 liters

Ranked causes

1. Indicator storage battery depleted or faulty (unknown)

First check

Activate indicator test switch and verify battery power

Test point: Liquid crystal digital display on quantity indicator
Expected: Display shows reading between 10.00 and 19.99 liters, 10.00 to 19.99

Liquid oxygen skin contact patient safety

Skin exposed to liquid oxygen drops or splashes freezes immediately, causing severe frostbite and frozen tissue.

Ranked causes

1. Operator handling error or equipment malfunction causing spillage (occasional)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Loud or continuous hissing sound with vapor visible patient safety

Audible hissing from container assembly vent line that is loud and continuous, or vapor is observed venting

Ranked causes

1. Abnormal venting or pressure release from container assembly (unknown)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

LOX converter contaminated patient safety

Converter contaminated with undesirable odors, moisture or foreign substances

Ranked causes

1. Contamination from non-compatible materials during servicing (unknown)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Oxygen delivery pressure falls below 45 PSIG at 15 LPM

During flow check at 15 LPM setting, measured pressure at outlet drops below minimum of 45 PSIG

Ranked causes

1. Insufficient pressure regulation or supply pressure low (unknown)

First check

Check oxygen delivery pressure at 15 LPM flow setting

Test point: Supply outlet after flow control valve set to 15 LPM
Expected: Pressure does not fall below 45 PSIG

Oxygen equipment near combustible materials patient safety

Risk of spontaneous ignition or rapid combustion when liquid oxygen equipment is near hydrocarbons or absorbent materials

Ranked causes

1. LOX equipment proximity to incompatible substances (common)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Oxygen odor detected other than normal hose smell patient safety

Emitted oxygen smells of substances other than the normal hose odor during flow check

Ranked causes

1. Contamination in oxygen system (unknown)

First check

Smell emitted oxygen for any odors

Test point: Oxygen outlet at 15 LPM
Expected: Normal hose smell only

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Oxygen supply consumed too quickly patient safety

Pressure or quantity decreases faster than normal during use

Ranked causes

1. System leakage (common)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Pressure gauge calibration check high voltage

Verify converter pressure gauge accuracy against calibrated master gauge

Ranked causes

1. Pressure gauge requires calibration verification (common)

First check

Fill container assembly with liquid oxygen

Test point: Filler valve
Expected: Container filled with liquid oxygen

11 more checks with pass and fail actions, 1 corrective action, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Pressure regulator calibration check high voltage

Verify pressure regulator output against master gauge during operation

Ranked causes

1. Regulator requires pressure testing and adjustment (common)

First check

Remove front panel screws and panel

Test point: Container assembly front
Expected: Panel removed to access regulator

11 more checks with pass and fail actions, 1 corrective action, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Quantity indicator battery power depleted

Indicator does not display reading when membrane test switch activated

Ranked causes

1. BA-3090/U batteries discharged or missing (common)

First check

Activate membrane test switch and observe reading

Test point: Quantity indicator display
Expected: Reading between 10.00 and 19.99

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Quantity indicator display not responding

Quantity indicator does not show reading when TEST switch is actuated; battery power may be insufficient

Ranked causes

1. Quantity indicator storage battery depleted (common)

First check

Verify quantity indicator battery power by activating TEST switch

Test point: Quantity indicator display
Expected: Reading between 10.00 and 19.99

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Reverse connection of flow control valve inlet and outlet patient safety

Flow control valve connected with inlet to humidifier and outlet to container assembly instead of correct orientation

Ranked causes

1. Operator connected valve fittings in reverse order (unknown)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Reverse inlet/outlet connection patient safety

Flow control valve fittings connected in reverse order or supplied with incorrect gas source pressure, causing inaccurate oxygen flow and potential patient injury.

Ranked causes

1. Inlet/outlet fitting reversed or incorrect gas source (not 50±5 psi oxygen) (occasional)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Unobstructed vent line required high voltage

Vent line or fitting becomes obstructed, preventing safe pressure release from liquid oxygen expansion.

Ranked causes

1. Vent line/fitting obstruction (common)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Vent line obstruction high voltage

Pressure buildup when liquid oxygen expands to gas with obstructed vent line or fitting

Ranked causes

1. Vent line or fitting blocked or obstructed (common)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Community

0 fixes logged by technicians through their AI, with outcomes, for this model.

ServiceForge knowledge base record. Field-unverified unless technicians confirmed it. A teaching summary of the record, not a service manual. Export 2026-10-14.