JT Cooler

1   Safety

2   Principles of Operation

3   Normal Operations

4   Routine Maintenance

5   Non Scheduled Maintenance

6   System Interconnections

7   Dewar Schematic and Temperature Sensor Positions

8   Operating Log Sheets

9   Operational Test Results

10  Quantum Cooler J-20 Compressor

11  Closed Cycle Water Cooler

1. Safety

1.1 Hazards

The Quantumcooler Liquefier/Reliquefier produces liquid helium. Consequently, like all equipment using cryogens, certain hazards are present.

The Quantumcooler System is equipped with a number safety relief valves and other safety features which protect the system. These must not be tampered with.

  Improper use of this liquefier could pose a hazard to personnel and property.

The potential hazards are catastrophic rupture if unvented vessels, freezing damage from splashing cryogens and asphyxiation hazard from high concentrations of helium gas. It is the customers responsibility to ensure that the installation is monitored so that a cooling water leak near a compressor would not cause any damage.

Catastrophic rupture can occur if a cryogen is held in a sealed container while warming. The high pressures generated can burst the container, resulting in a hazard. All cold vessels including the vaccum space within the Quantumcooler are equipped with safety relief valves

1.2 Asphyxiation Hazard

No catastrophic ruptures nor asphyxiation hazard conditions have been reported with Quantum equipment. This section of the manual is not intended to alarm the user but rather to explain the purpose of the numerous safety features.

High concentrations of helium gas in a room constitute an asphyxiation hazard. Although non-poisonous, the gas may reduce the concentration of oxygen below safe levels. When the helium concentration is extremely high, then the oxygen in solution in the blood will diffuse out causing a rapid collapse and possible death.

  Every year people die when inhaling helium gas to try the "squeaky voice trick". A single deep inhalation of helium gas can be fatal. It is strongly recommended that this "trick" not be attempted.

In small rooms of confined spaces where there is insufficient natural ventilation, or where
the volume of helium which could potentially be released exceeds 20% of the room
volume it is recommended that a low oxygen meter with an audible alarm be permanently
installed at shoulder height in the liquefier room. A placard advising non-entry in the
event of an alarm should be affixed to the outside of the room.

2.0 Principles of Operation

2.1 Principles of Operation

   Values given here are for illustration only. Always refer to Section 3.3, Recommended Pressures & Settings for system adjustment.

The Quantumcooler Liquefier/Reliquefier is a three stage closed-cycle refrigerator. See section 7.0, Dewar Schematic. The working fluid in all three stages is an extremely high purity helium gas. The nominal operating temperatures of the three stages are 70K, 15K and 4.2K respectively. The first two stages are based on the Gifford-McMahon (G-M) cycle with helium gas pressure cycled isothermally from 19 bar relative (275 psig) to 5 bar relative (73 psig). The two G-M stages are linked together and share a single displacer-regenerator. The upper(large diameter) portion of the displacer is packed with wire screens and the lower (small diameter) portion is packed with lead shot to provide sufficient heat capacity for regeneration. Moving seals force the helium gas through the regeneration media in the centre of each displacer.

The third stage of refrigeration is a Joule-Thomson (J-T) isenthalpic expansion stage. Extremely high purity J-T supply gas at 17 bar relative (250 psig) is cooled to 13K by the previous two G-M stages. This gas then flows through a counterflow heat exchanger which cools it to 4.2K and then passes through a J-T orifice producing a cold mixture of gas and liquid at 1 bar absolute (atmospheric pressure). The liquid fraction is evaporated in heat STN. #3 to provide cooling for liquefaction. Gas and liquid leave the station still at 4.2K. This cold material returns via the counterflow heat exchanger to the 13K stage, thereby cooling the incoming high pressure gas.

Please refer to Drawing D93000 Appendix E.

3 Normal Operation

If the presence of air is suspected in the system, it must be decontaminated prior to cooldown. See section on decontaminating helium gas supply.

3.1 Start-up

Record all pressures and temperatures on the system log sheet BEFORE starting and during cooldown. Perform other adjustments as required by the G-M Manual.

(a) Turn on the cooling water to the water cooled compressors. The flow through all compressors should be such that when operating the water outlet temperature is below 45C.

(b) Prior to and during cool-down, monitor and record temperatures on the attached system logsheet. It is very useful to compare these temperatures with the standard cool-down curve given the Test Results section.

(c) The J-T valve is a very fine needle valve and can easily be damaged by overtightening. Never attempt to fully close this valve as it may be damaged. Leave the J-T valve at the factory setting (see section 3.3).

(d) Check that the helium pressure in the J-T / G-M loops are at the recommended pressure (see section 3.3).

(e) Start the GM compressor and turn on cold head.

(f) Start the JT compressor. When the pressures stabilise, adjust the regulator on the back of the compressor for a JT return pressure as shown in the recommended pressure table.

(g) Set JT valve to 2 turns open initial setting.

(h) Check that the cooling water discharge temperature does not exceed 45C.

(i) Open the JT-"Bypass" valve approximately 3 - 4 turns, and leave open until the 3rd stage temperature approximates 40 degrees Kelvin, at this time the "Bypass" valve should be adjusted to approximately 2 turns open. When the 3rd stage temperature reaches approximately 20 degrees Kelvin, then close the "Bypass" valve to "0" turns open. Do not attempt to close the Bypass valve passed the "0" mark on the dial counter knob. Severe damage can result.

   THESE VALVES ARE DELICATE AND CAN BE DAMAGED BY OVERTIGHTENING. INCREASING NUMBERS INDICATE INCREASED FLOW.

3.2 System Shutdown

Switch the JT and GM compressors of and then shut off the cooling water.

IMPORTANT: Do not disconnect any of the flexible hoses until after the system has warmed to room temperature. Disconnecting the self-sealing coupling before allowing a warm-up will result in overpressures in the cryogenic piping and destruction of the cryocooler. QUANTUM TECHNOLOGY CORP. IS NOT RESOPONSIBLE FOR ANY DAMAGE CAUSED BY MISUSE.

3.3 Recommended Pressures & Settings

Notes:

1) Read JT Return gauge on compressor. Adjusted with JT valve. The valve at the back of the JT compressor should be fully closed (fully clockwise).

2) No gauge, set by regulator on buffer tank.

3) Set while warm by initial charge (quantity) of helium in the system.

4) JT valve useful range is 0 turns open to 4.0 turns open. When changing the setting, avoid backlash by opening the valve a full turn before closing the new setpoint desired.

5) Adjusted by regulator on buffer tank, read gauge on GM compressor outlet.

4.0 Routine Maintenance

4.1 G-M Circuit Maintenance

The G-M adsorber must be replaced every 10,000 hours of operation (Quantum part number MODEL Q-ADSORBER-SC)

4.2 Cold-Head Maintenance

When cooling power diminishes after 12,000-17,000 hours of operation, the model 1020 cold heads will require a maintenance kit overhaul of seals (Quantum part number Q-1020-KIT).

4.3 Compressor Maintenance

In the event of an overtemperature condition they will switch off and restart after cooling down. In the event of a total pressure loss they will switch off.

The lubricant is in a closed-loop. In the event of low lubricant level (which can only occur in the event of a failure in the lubricant recovery circuit), they become very noisy as the remaining lubricant slugs its way through in pulses of a few seconds duration. In this event, switch the compressor off before damage occurs.

The compressors are not field serviceable. In the event of difficulties, they must be returned to the factory for service

4.5 Decontaminating the JT Loop

In closed-cycle operation, contaminants gradually accumulate by freezing out at the J-T valve. These may eventually cause the J-T flow to stop and the system will warm up to the G-M second stage temperature.

Symptoms are: Third stage temperature (normally 4K) will be at 15K or above. Second stage temperature below 15K. No flow through JT loop results in a very low (vacuum pressure of - 0.5 bar = - 15''Hg) on the JT compressor return line.

If the G-M cooler is switched off and the system is allowed to warm up to room temperature, the contaminants will clear themselves; the cryocooler may then be restarted and it will operate for some time before becoming plugged again. However, in this procedure the contaminants remain trapped in the J-T loop.

4.5.1 Minor Contamination of the J-T Loop

After some time (especially within 1 day of initial installation of charges to the system).contaminants may accumulate/freeze in the J-T loop, reducing the J-T loop flow. Refer to the J-T loop flow diagram.

  This procedure, if not followed correctly may result in overpressure in the JT loop and destruction of the heat exchanges. Quantum will not be responsible for damages caused by overpressures.

• Before starting: Ensure that two relief manifolds P7 and P8 are still installed on top of the liquefier.

BACKFLUSH METHOD:

(a) While the system is cold, switch off the JT compressor. Before disconnecting Aeroquips ensure that JT return pressure is above atmospheric. The valve on the buffer tank should be fully opened to allow pressure equalisation;

(b) After JT return pressure has equalised disconnect the JT supply and return lines going to the JT compressor.

(c) Switch off the G-M compressor;

(d) Connect the service manifold P20 to the JT supply sides at the end of the hose, which was disconnected from the cross P5. Using a hexagonal Allen wrench the relief valve R100 pressure setting should be reduced to 50 psi;

(e) Allow the system to warm to room temperature (the J-T loop will vent through the relief valve R100);

(f) Connect pure helium gas to the JT return at the end of the hose which was disconnected from the compressor;

(g) Open V102 and allow it to vent down to 15 psig (1 bar), then quickly close V102;

(h) Pressurise the JT loop to 240 psig (8 bar). Then close valve;

(i) Repeat (f) and (g) a total of 40 times;

(j) Remove the service manifolds and reconnect the lines to the compressor and restart the system.

 

4.5.2 Major Contamination of the J-T Loop

In some circumstances (major leaks, component failure etc.), the JT loop may become exposed to air. This large quantity of air must be removed with the following procedures. Perform the following steps with the liquefier OFF and WARM.

(a) Turn all compressors, JT's and GM OFF. Wait for liquefier to warm to room temperature;

(b) Connect the system as shown in the diagram "GM/JT Interconnections";

(c) Connect the pure helium supply to V103;

(d) Carefully purge the regulator and connecting line;

(e) Bleed down the JT loop SLOWLY to 5psi through V102 (NOTE: This should take about 1 hour). Excessive speed may cause the lubricant to migrate out of the compressor and seriously contaminate the JT loop;

(f) SLOWLY (1 hour) repressurize the JT loop, through V103, to the normal charge pressure as listed in section 3.3. Then operate the JT loop for 15 minutes with the bypass valve fully open;

(g) Repeat (e) and (f) two times and

(h) The system may be operated with the service manifolds in place or removed as desired. Normal practice is to remove the manifolds so as to reduce the risk of leakage.

4.6 Purification of GM compressor

NOTE: The JT circuit requires higher purity than the normal operating purity of the GM circuit. Consequently, it is necessary to clean the GM circuit and GM coldhead prior to connecting to the JT circuit.

1 With GM compressor connected to GM coldhead only, operate coldhead for at least 4 hours. This allows the impurities (water & air) to freeze in the GM coldhead.

2 While it's still cold, turn off compressor and immediately disconnect GM return and GM supply lines from the coldhead
NOTE: This keeps the contamination in the coldhead. The compressor, lines and adsorber are all clean now.

3 Connect vent Aeroquip adapter to GM return on the coldhead to depressurize the coldhead.

4 Allow the coldhead to warm up to room temperature.

 

5 Connect a supply of pure Helium gas at 150 psi to the GM supply fitting of the coldhead.

6 Disconnect the vent line from the Gm return.

7 Run the coldhead electrical without any helium flow through it for five minutes.

8 While coldhead still running, alternately pressurised the coldhead to 150 psi and then depressurise, always pressuring through the GM supply line and depressurising through the GM return line.

9 Repeat 7 & 8 five times for a total of 25 charges.

10 With the coldhead pressurised, disconnect the lines. It is now clean and ready to use.

   This long purging sequence is necessary to remove the water from the coldhead.

5 Non-Scheduled Maintenance

Non-scheduled maintenance may be required in the event of a component failure or of exposure of any part of the extremely high purity helium system to the atmosphere.

Special procedures, tools and equipment are necessary for non-scheduled maintenance. Contact Quantum Technology Corp. for further information before proceeding.

Quantum Technology Corp. Quantum Technology Corp.
1370 Alpha Lake Road, Unit #15 250 H Street, PO Box 8110-183
Whistler, B.C. Blaine, WA
Canada, VON 1B1 USA, 98230
Phone: (604) 938-0030 Phone: (360) 647-9211
Fax: (604) 938-0061 Fax: (360) 671-2955
e-mail: quantum@whistler.net

5.1 Re-evacuating the Vacuum Dewar

Occasional pumping on the vacuum dewar may be required to compensate for outgassing of the superinsulation. If the superinsulation is ever exposed to helium gas, it will be necessary to pump for 24 hours to remove the helium.

(a) Warm the dewar to room temperature.

(b) Connect a clean vacuum pumping line to the closer dewar vacuum valve and to a good vacuum pump with liquid nitrogen trap capable of reaching less than 0.1 microns of Hg pressure.

(c) Evacuate the connecting line and ensure that it does not leak by checking the pump's vacuum gauge.

(d) Fully open the vacuum pumping valve.

(e) Pump until the vacuum dewar reads 100u or less.

(f) Close the valve and cap the port.

   If the pressure reads less than 100 microns at room temperature, it is normally not necessary to use a vacuum pump as the liquefier will cryopump itself as it cools (unless the residual gas is helium).

6 System Interconnections

The system interconnections are shown in the following figure.

- GM/JT Interconnections

7   Dewar Schematic and Temperature Sensor Positions

7.1 Sensor Calibration Data

8   Operating Log Sheets

9   Operational Test Results

9.2 Cooling Power Results

10   Quantum Cooler J-20 Compressor

The Quantum Cooler J20 is a highly reliable, single stage, water cooled, oil lubricated scroll compressor. The refrigerant is gaseous Helium.

The compressor is maintenance free.

Cooling water of sufficient flow and temperature is required to circulate through the compressor to prevent overheating. The definitive parameter is that the cooling water at the outlet of the compressor should not exceed 30 C. The flow thus depends on the inlet temperature. For a typical input temperature of 10 C with a typical heat load of 4kW, the minimum flow of water at 10C is 4000W/((30C-10C)* 4.19J/grC) = 50gr/sec = 3L/m. To achieve this flow requires a nominal pressure difference of 20PSI or about 1 BAR.

In the event of over temperature the compressor will switch off and restart after cooling down.

In the event of a Helium pressure loss it will shut down at 30PSI outlet pressure.

The lubricant is in a closed loop. In the event of a low lubricant level due to a recovery failure the compressor becomes very noisy. The level at the sight glass will have also fallen to empty. In this event switch the compressor off and get in touch with Quantum Technology Corporation.

The compressor is not field serviceable. In the event of difficulties is should be returned to the factory for service.

Quantum J-20 Compressor Parts Description

P1	inlet pressure gauge
P2	outlet pressure gauge
CV	check valve
Compressor	5KW scroll compressor
VBYPASS	forms a loop between compressor outlet and inlet, used as a dummy load for testing compressors.
SG1	sight glass shows oil leaving compressor. While compressor is running sight glass should always show a steady mix of gas & oil rushing by.
SG2	sight glass shows level of oil in buffer tank. Should always read somewhere between full and empty.
SG3	1st stage oil separator sight glass. May show very slow flow of gas bubbles and oil travelling upwards.
SG4	2nd stage oil separator sight glass. May show very slow flow of gas bubbles and oil travelling upwards.
SG5	3rd stage oil separator sight glass. Should never show flow of gas and oil.
VT1&VT2	bypass valves can be used to change 1st and 2nd stage oil separators. Should always be closed.
VHe-CHG	Helium charging port valve
SG6	Oil detector sight glass. Should always by dry.
PRV	375 PSI pressure relief valve
PS1	pressure switch. -	For GM compressors:   -For JT compressors:	off>400PSI off< 35PSI off>150PSI off< 35PSI
pressure switches have a noticeable amount of hysterisies.
T1-T3	oil separators
BUF	oil buffer tank
VLUBE-CHG	oil charge port valve
CB1	10 A circuit breaker
C1	3 phase motor contractor
T1	480V -120V step down transformer
CB2	1 A circuit breaker (push to reset
SW1	SPDT toggle switch. Compressor can be controlled remotely when switch is open.
R1	24VDC relay, supplying 24VDC to pins 1 and 3 of the 14 pin connector at the rear of the compressor allows the compressor to be switched on and off remotely.

11  Closed Cycle Water Cooler

Installation Instructions

1 Remove hose connecting the coolant "in" and "out" of the green radiator. A small amount of coolant spillage is normal.

2 Connect a long hose from the compressor "water out" to the radiator "water in".

3 Connect the other long hose from the compressor "water in" to the radiator "water out".

4 Pressurise the system (with air) to 20 PSI by way of the schrader valve on the bottom of the orange diaphram tank.

5 Apply power (220V 50Hz)

6 Since the volume of air trapped in the hoses and compressor will eventually escape out the air relief vent (above fill valve) the pressure of the system will drop as the air escapes. It is necessary to periodically re-pressurise the system to 20 PSI until all of the air has escaped. Provided that the system is running this should not take longer than a day or two.

Operational Instructions

1 Water out of the compressor should not exceed 60 DegC. Water into the compressor should not exceed 35 DegC.

2 If there is a situation where the ambient temperature of the location of the radiator exceeds 30 DegC it will not work. The radiator gives off over 3KW of energy in the form of heat so make sure this will not be a problem in the location chosen.

3 If there is a situation where the temperature of the coolant exceeds the maximum, (aprox. 65DegC) the compressor will shut down and the high temperature trip has to be manually reset. (back of compressor)