Operating Instructions
SAFETY
Before using any cryogenic refrigerator, read the Handle with Care booklet provided with the unit. It details safety precautions that must be understood before using the equipment. If a replacement booklet is needed, order publication TW-10 Handle with Care from your supplier.
Following are a few of the safety precautions described in the Handle with Care booklet. Please be sure to read the entire booklet.
Store and use these containers only in well ventilated areas. In a confined area, nitrogen
gas from these units may cause suffocation by displacing air needed for breathing. Install a suitable oxygen monitor.
Do not touch liquid or cold metal surfaces with your bare skin. The liquid nitrogen
refrigerant is extremely cold: -196°C (-320°F). Exposure to skin or eyes to liquid, cold gas or frosted parts could result in a severe frostbitelike injury. Because of the extremely low temperature, a face shield and gloves must be worn when transferring liquid nitrogen and material into or out of these containers.
Use only the necktube covers supplied with this unit or a listed replacement part. A tight fitting plug or stopper will cause a pressure increase in the container that may damage the container and/or cause personal injury.
OPERATION
Filling: Adding liquid nitrogen to a warm container may cause splashing and will generate a significant volume of nitrogen gas as cold liquid contacts warm refrigerator surfaces. Add liquid slowly to minimize these effects. Be sure there is adequate ventilation. Keep your head clear of the heavy volume of vapor that may be produced. It is extremely cold and could cause personal injury.
WARNING:
DO NOT OVERFILL. Over-filling may result in personal injury due to liquid spillage.
DETERMINING LIQUID LEVEL
Liquid level must be checked at regular intervals – refrigeration depends on the pressure of liquid nitrogen. The liquid level in the container can be determined with a dipstick. Insert the dipstick straight into the container so that it rests on the rack positioning fixture on the bottom of the unit. After 5 to 10 seconds, withdraw the dipstick and wave it back and forth in the air. A frosted section will form representing the depth of the liquid in the container.
WARNING
Never use hollow rods or tubes as dipsticks. When a warm tube is inserted into liquid nitrogen, liquid will spout from the top of the tube and may cause personal
injury.
The liquid level chart shows volume of liquid nitrogen vs. depth for LS Series refrigerators.
These values are approximate and are based on a standard condition with no stored material in the container. With store material, the liquid volume will be slightly less than the value of the chart.
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LQ |
OLWHUV FP |
OLWHUV |
/6 /6 /6 |
LQ |
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INSERTING OR REMOVING RACKS
To prevent unnecessary loss of liquid nitrogen and accumulation of ice, the necktube core (the stopper) should remain in the container when the stored material is not being accessed. When accessing stored material, the necktube should be removed as briefly as possible.
When removing material from the racks, withdraw the rack just far enough to remove contents. Completely withdrawing the rack will unnecessarily
expose the stored material to warm room temperature conditions.
WARNING
Some boxes have liquid drain openings, some do not. If racks are completely removed from the container, liquid nitrogen may remain in the either rack and boxes, or simply drain from the bottom. When removing racks, stop briefly at the necktube to allow liquid to drain completely, then
handle the rack carefully to prevent personal injury. Avoid direct rack contact with bare skin. The use of proper personal protective gear is strongly urged – cryogenic gloves, face shield and gown – to protect against splashing.
When room temperature is added, slowly lower the rack into the refrigerator to reduce the boiling of refrigerant and the surge of cold nitrogen gas. When inserting the rack, tilt the bottom of the rack in the direction of the index ring notch. The numbers and colors on the rack handles are a convenient aid to inventory control.
SECURING CONTENTS
The contents of all models may be secured with a seal or lock through tabs on the edge of the lid opposite the hinge.
ROUTINE CARE AND MAINTENANCE
If ice accumulates inside the necktube, a general cleaning of the refrigerator should be scheduled as soon as the stored material can
TW-348
Systems
Laboratory
LS SERIES
AUTO FILL OPERATION
WARNING: In order to prevent the relief device on nitrogen refrigerator(s) from opening when the system is in operation, the liquid nitrogen supply system must be protected by a pressure relief device that will open when the pressure at the inlet to the refrigerator(s) is approximately 22 psig (1.5 bar/152 kPa). Never install the supply system pressure relief device into a liquid service line.
Filling the Refrigerator (Initial Fill)
The LS6000-AT uses the AutoTend controller that comes preset from the factory to operate.
The liquid nitrogen supply pressure at the inlet to the unit should be in the range of 10 psig (0.7 bar/69 kPa) to 20 psig (1.4 bar/138 kPa) for optimum performance. Higher operating pressures will increase transfer losses and create excessive turbulence of the liquid in the unit which can generate false signals to the liquid level controller causing the unit to underfill. In “liquid phase” storage applications, excessive turbulence can cause splashing which could result in personal injury and/or damage to the unit.
If the liquid nitrogen supply pressure at the inlet to the unit rises above the opening pressure of the relief valve on the unit, liquid nitrogen will be discharged into surrounding area which can cause rapid and very dangerous depletion of oxygen in the atmosphere. Once this pressure relief device has opened and cooled to liquid nitrogen temperature, it will not reset until it has warmed to near ambient temperature. THIS COULD PERMIT THE ENTIRE CONTENTS OF THE LIQUID NITROGEN SUPPLY SYSTEM TO BE DISCHARGED INTO THE IMMEDIATE AREA OF THE REFRIGERATOR(S).
WARNING: Maintain adequate ventilation to prevent asphyxiation hazard. (See Safety Precautions)
Power Supply Connection
Connect the 24 Volt AC power supply to the rear of the cryostorage system; then plug the power supply into a 110/ 120 VAC outlet. (See Figure 5 for the Electrical Supply Connections.) Turn on the AutoTend by turning the key on the front panel (see Figure 5) to the “on” position. The audible alarm may sound during setup; silence the alarm by pressing the button labeled MUTE.
WARNING: If the fill fails to stop for any reason, quickly close the liquid supply valve to prevent overfilling until the cause of the problem can be determined.
The unit is now under automatic fill control. Liquid will be added by the controller as long as the liquid supply and electrical power are maintained.
Operating Parameters
When materials are immersed in liquid nitrogen, they will assume the temperature of the liquid -320° F (-196° C). When material is stored in the vapor phase of the liquid, the liquid nitrogen is still a very cold refrigerant, but the unit’s interior temperature increases somewhat as product is stored higher above the liquid. This temperature differential is not significant in many biological storage applications, and is affected by the amount of product stored in the unit, the type and size of inventory control system, and the liquid level in the unit.
The liquid level in the unit is determined by the position of the sensor probes in the tube located next to the fill tube. These probes are set at installation to maintain a specific liquid level. (See Figure 4) The cycle repeats when the liquid level drops to the low level sensor over time. Sensor probes may be moved to define new high and low levels, and these levels may be set independently to vary the liquid level differential between fills. For adjusting the temperature probes see “Changing Liquid Level” section in this manual.
Vapor Phase Storage
Vapor phase storage is normally utilized when stored product is unable to withstand liquid nitrogen temperatures, or when the storage medium (vials, ampules, etc.) is not designed for liquid phase storage.
In a typical vapor phase storage system, the liquid level sensors are positioned to maintain the liquid level at or below the top of the spider. This positioning allows stored product to be kept at cryogenic temperatures without being exposed to liquid nitrogen, reducing the possibility of leakage or crosscontamination. Care must be taken in the positioning of the level of refrigerant in the event of power outages, which may disable the controller for an extended period of time. Consideration must also be given to liquid nitrogen availability and delivery schedules.
Liquid Phase Storage
Liquid phase storage is normally utilized when liquid nitrogen temperatures are required to maintain stored product viability and the storage mediums are adequate for storage in liquid nitrogen.
In a typical liquid phase storage system, the liquid level sensors are positioned to maintain the liquid level at or below the top level of the inventory control system. During operation, the upper levels of the inventory control system will at times become exposed as the liquid level fluctuates.
Care must be taken to ensure that the liquid level remains below the bottom of the lid. Operating the refrigerator with high liquid levels characteristic of liquid phase storage may result in turbulence during fill cycles. Caution must be exercised if the unit lid is opened during a fill, and appropriated safety equipment should always be worn.
Sensor Positioning for the AutoTend Controller
The longer sensor probe (orange/yellow wires) contains the Low Level sensor in a pod. The shorter probe (red/black wires) contains the High Level sensor. The factory sensor positions will maintain a liquid level between 2.0 in. to 4.0 in. The dimensions used for the factory sensor installation are shown in Figure 2.
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