PLEASE READ: Very important guidelines for using this document
How to make contact with Oxford Cryosystems
Nitrogen Circuit Gas Leak Test
Stainless Steel Line Drier Unit
Condensation and/or ice over the outside of the Cryostream transfer line or blue can indicates a loss of vacuum. This should not be confused with localised spots of ice or condensation. Remember, its impossible to lose a vacuum from one small area of vacuum space! This loss of vacuum can be for two reasons:
Consult the instruction manual on repumping the vacuum and be sure to protect the Pumpout Port and Relief Valve when refilling.
If it is believed there is a leaky joint or cracked flexible hose, contact Oxford Cryosystems or your local agent as this is not user servicable.
Inability to reach low temperatures and the base temperature begins to rise
This is due to the flexible line being bent too sharply beyond its 200mm minimum radius and the transfer capillary inside the flexible vacuum jacket touches the wall of the vacuum jacket.
Cryostream will continue to run happily like this, but it may be worth contacting Oxford Cryosystems or your local agent. Try to increase the bend radius at the point where the ice spot occurs.
This is due to an unbalance in the heat exchanger inside the Coldhead of Cryostream.
Cryostream requires 5 litres/minute of gas along both paths of its heat exchanger so the 5 litres of gas in the SUCT path can absorb the heat from the 5 litres of gas in the FLOW path. If gas has leaked out between the gas exiting the SUCT side of the heat exchanger (SUCT connector on the top of the Coldhead,) and entering the FLOW side of the heat exchanger (FLOW connector on the top of the Coldhead,) excess cold gas spills out into the nylon tubing in the SUCT connector causing condensation and icing.
Check to make sure all the nylon tubing is pushed 15-16mm into each quick-fit connector on the Cryostream then perform the Nitrogen Circuit Gas Leak Test run the system again and if the problem persists Oxford Cryosystems or your local agent of your findings.
Spitting of liquid nitrogen from the nozzle
If the dewar is open to the atmosphere, it is common for ice to build up at the interface between the warm air and the cold gas eminating from the dewar. This ice can fall into the dewar and contaminate the nitrogen as its concentration builds up.
Find a way to cover the dewar opening. This can be done quite comprehensively but BE SURE NOT TO SEAL THE DEWAR. Simply plugging the dewar with a cloth will prevent most atmospheric moisture getting into the dewar but more elaborate setups involve clamping a bung on to the top of the dewar and then drilling holes for the Cryostream leg, venting and refilling. If the dewar is sealed up, a vent hole is VERY important otherwise Cryostream will NOT work.
Controller Status reads 'Ice Block warning will trip at 2 l/min'
Cryostream Shutdown due to ice block
Cryostream Shutdown due to low flow after a few seconds of running
Cryostream Shutdown due to low flow - no explicable reason
If the gas temperature will not drop below a certain temperature, (for example, the programmed gas temperature is 100K and Cryostream will only reach 105K but stable and not rising,) there are two possible causes:
Manually adjust your Evaporator setting. Please see your manual for this procedure. If the base gas temperature that Cryostream reaches continues to rise, it is likely the vacuum is degrading and will require repumping. See the manual for this procedure.
Condensation and/or ice covering the outside of the blue Coldhead or the flexible transfer line
Inability to reach low temperatures and the base temperature begins to rise
Cryostream maintains an error of a few degrees that disappears when the dewar is topped up
These symptoms indicate a loss of vacuum. This loss of vacuum can be for two reasons:
Repump the vacuum and be sure to protect the Pumpout Port and Relief Valve when refilling the dewar with nitrogen.
Condensation and/or ice covering the outside of the blue Coldhead or the flexible transfer line
Inability to reach low temperatures
Cryostream has detected the beginnings of a ice block inside the Coldhead. The ice block is detected by a pressure switch in the controller and is designed to give the user an advance warning of an ice block that will eventually cause the system to trip.
This is due to a build up of ice in the FLOW path capillary of the heat exchanger. The water vapour in the nitrogen gas freezes out onto the wall of the capillary of the heat exchanger and eventually blocks. It is not blocked by large particles of ice but the slow narrowing of the capillary wall at the water vapour freezes out. If the Cryostream has been running well up to this point, it may continue to run for long enough to finish a data collection. The next symptom to be seen is a gradual fall in the nitrogen gas flow rate.
There are two possible sources for the water vapour:
First, to remove the ice block, let your system warm up over night. The EvapT value on the controller must reach room temperature as this indicates that the ice block has melted. When the system is restarted, the water vapour will blow, unnoticed, out of the end of the nozzle. If the Cryostream is require for use and it can not be left over night, disconnect the dry air supply for Cryostream at the top of the nozzle and reconnect it to the FLOW connector on the top of the Coldhead. IMPORTANT: Reduce the flow on the dry air supply to less than 10 litres/minute to avoid any damage to the Gas Sensor in the nozzle.
Ice in your nitrogen supply - empty the dewar vessel and let it warm up to room temperature. Mop up any moisture in the bottom. Check on the purity of your liquid nitrogen by shining a flashlight into the dewar. The liquid should look clean like water but do not worry if you see a few particles in the bottom, this is fairly normal. If your liquid nitrogen is milky, you have a chronic contamination of ice, Cryostream can not handle this so talk to your liquid nitrogen supplier. Try to avoid pushing the rigid leg of Cryostream into the bottom of the dewar, this prevents particles in the bottom of the dewar being sucked up the leg.
An inward leak - Check to make sure all the nylon tubing is pushed 15-16mm into each quick-fit connector then perform the Nitrogen Circuit Gas Leak Test and inform Oxford Cryosystems or your local agent of your findings. Do not rush into changing a diaphragm as opening up the gas pump can often cause a leak. The diaphramg in the grey gas pump will last for approximately one year of continuous running. Speak to Oxford Cryosystems first.
Once the ice contamination problem has been rectified, fit an Oxford Cryosystems Line Drier Unit. If there is already one in circuit, it will now be contaminated and will require reactivation (see instructions). DO NOT fit a new one or a reactivated one until you have rectified the ice contamination. You will create unnecessary work and confusion for yourself.
Cryostream Shutdown due to ice block
Ice formation on the sample can begin at the point of flash freezing the sample or can build up over time to eventually cover the sample and ruin the diffraction image.
Please note: Ice on the sample does not come from the nitrogen gas travelling down the nozzle. Nitrogen gas from Cryostream is very dry (circa 0.1ppm of water vapour).
Ice on the thin film supporting the crystal in the loop can arise from a number of sources.
To increase the effectiveness of the cryoprotectant, increase its concentration.
Position the nozzle as close to the sample as possible without effecting the path of the x-rays or casting an image on to the detector. The ideal distance is inside the first 6mm from the end of the nozzle and the centre 4mm cross section. Be sure to clean the loop before use as ice build up will only compound the problem.
Check the laboratory for drafts. The most likely cause of turbulence is an air conditioning unit or a cooling fan from an x-ray generator. Create a screen between the source of the draft and your cold stream. This will reduce the turbulence greatly. If you are unsure of the source of the draft, try the Flashlight Test.
Try adjusting the flow of the outer dry gas stream. In a draft-free environment 7-8 litres per minute is fine but when the air is more turbulant, try turning the outer stream flow rate up to 12 or 13 litres per minute, this can often cure the problem. (See Flashlight Test)
If the icing persists and there is also a concentric build up of ice on the nozzle, the most likely cause is a wet dry air supply. If you have an Oxford Cryosystems Dry Air Unit change the Compressor Filter Delivery Element. If the icing persists, contact Oxford Cryosystems or your local agent about a Dry Air Unit service.
Concentric formation of ice around the nozzle
Feather of ice forming from inside the cold stream nozzle and extending towards sample
An ice build up of this type is caused by a disturbance of the laminar flow system where the cold stream mixes with the outer dry air stream and atmospheric moisture. This is due to drafts in the laboratory or a foreign body in the Cryostream nozzle.
Check the laboratory for drafts. The most likely cause of turbulence is an air conditioning unit or a cooling fan from an x-ray generator. Create a screen between the source of the draft and the cold stream. This will reduce the turbulence greatly. If you are unsure of the source of the draft, try the Flashlight Test.
Try adjusting the outer dry gas stream. In a draft-free environment 7-8 litres/minute is fine but when the air is more turbulant, try turning the outer stream flow rate up to 12 or 13 litres per minute, this can often cure the problem. (See Flashlight Test)
If the ice build up continues, look carefully up the nozzle to make sure there are no obvious foreign bodies disturbing the laminar flow system (eg. blob of solder or modelling clay), if there is, contact Oxford Cryosystems or your local agent, immediately, DO NOT TRY TO REMOVE THE OBJECT WITHOUT SPEAKING TO US FIRST. Damage to the Gas Sensor is expensive and time consuming to fix.
Concentric formation of ice around the nozzle
Ice formation on outer edge of the nitrogen gas cold stream nozzle
The likely cause of ice on one side only of the nitrogen nozzle is a misaligned dry air shroud tube. This is not the same as a feather of ice growing from inside the cold nitrogen gas nozzle.
Look up the nozzle of the Cryostream and check to make sure the outer dry air shroud is concentric with the inner nitrogen nozzle. A small misalignment may be corrected by pushing the inner nozzle to one side. The shroud tube is locked into its 26mm diameter mounting bush using a low strength retainer compound (eg Loctite 222e). To release the shroud tube, grasp it gently and push to one side to release the retainer bond. Movement of the shroud tube will be limited as it touches the outside of the inner nitrogen nozzle - this prevents the shroud tube from kinking. Once the outer dry air shroud has been removed, refit the shroud tube using a little retainer compound, check that the tube is concentric and allow the retainer to set.
Feather of ice forming from inside the cold stream nozzle and extending towards sample
This is likely to be wet air from the dry air supply or a high flow rate from the dry air supply. The cold stream requires a dry air shroud of dewpoint -60°C. If the stream is wet, the moisture in the air will freeze onto the nozzle and sample.
Make sure a unruly student has not turned the flow rate up to 25 litres/minute. If the Cryostream utilises an Oxford Cryosystems Dry Air Unit, change the Compressor Delivery Filter Element, a spare is provided. If the ice persists, contact Oxford Cryosystems or your local agent who will supply a service kit.
Feather of ice forming from inside the cold stream nozzle and extending towards sample
Ice formation on outer edge of the nitrogen gas cold stream nozzle
Spitting of liquid nitrogen is caused by recondensation of nitrogen gas in the FLOW path of the heat exchanger. This can be caused by a number of factors:
It is worth considering these solutions in order:
Localised icing on the Coldhead SUCT connector and tubing
There are a couple of possible causes of an unstable gas temperature:
It is worth considering these solutions in order:
Condensation and/or ice covering the outside of the blue Coldhead or the flexible transfer line
Spitting of liquid nitrogen from the nozzle
Localised icing on the Coldhead SUCT connector and tubing
Inability to reach low temperatures and the base temperature begins to rise
In the bottom five inches of the Cryostream transfer leg there is a Cryopump. This maintains the vacuum in Cryostream when plunged into liquid nitrogen. If the nitrogen level gets sufficiently low to uncover the Cryopump, the vacuum insulation can be weakened to cause the gas temperature to rise.
Top up the dewar. If the dewar is fitted with a level detector, make sure it is set up to refill before the Cryopump is exposed.
If, after a few seconds of running the pump can not generate any gas flow the system will shut down. The most likely cause of this is a restriction in transfer line from the dewar caused by a solid piece of matter (usually ice) restricting the flow of liquid nitrogen.
Take the leg out of the dewar vessel. Wait 15 minutes for the end of the leg to warm up to room temperature. Disconnect the dry air shroud gas from its connector at the top of the nozzle and reconnect it to the SUCT connector on top of the Coldhead. Set the gas flow to about 5 litres/minute. This will blow air down the Cryostream transfer line and will both remove any solid matter or ice from the line and dry it out.
Cryostream Shutdown due to low flow - no explicable reason
There are two possible causes Cryostream can not diagnose:
Cryostream Shutdown due to low flow after a few seconds of running
This is due to a build up of ice in the FLOW side of the heat exchanger. This ice has come from water vapour frozen out on the wall of the capillary of the heat exchanger. It is not blocks caused by large particles of ice but the slow narrowing of the FLOW path capillary wall at the water vapour freezes out.
There are two possible sources for the water vapour:
Ice in the nitrogen supply - small particles of ice are sucked up the leg and flexible transfer line into the Coldhead. These particles pass through the Evaporator Heater and along the SUCT path of the heat exchanger. The ice then passes out of the Coldhead along the tubing marked SUCT, through the controller, through the pump, back through the controller and back into the Coldhead along the tubing marked FLOW or DEL. During its course along the nylon tubing, the ice melts to water vapour which, on entry into the FLOW path of the heat exchanger, refreezes causing narrowing of the capillary and an impending ice block. ICE PARTICLES DO NOT CAUSE THE BLOCK, WATER VAPOUR THAT FREEZES CAUSES THE BLOCK.
Please note: There is no easy way of completely removing particles of ice from your nitrogen supply. This means you will get this warning eventually, so do not panic!!
An inward leak - Atmospheric moisture is sucked into the gas stream on the SUCT path of the gas flow circuit at some point. The likely cause of this is a nylon tube NOT pushed its full 15-16mm into the quick-fit connector. If all the tubing has been reseated properly, it is possible the diaphragm in the gas pump has split.
First, to remove the ice block, let your system warm up over night. The EvapT value on the controller must reach room temperature as this indicates that the ice block has melted. When the system is restarted, the water vapour will blow, unnoticed, out of the end of the nozzle. If the Cryostream is require for use and it can not be left over night, disconnect the dry air supply for Cryostream at the top of the nozzle and reconnect it to the FLOW connector on the top of the Coldhead. IMPORTANT: Reduce the flow on the dry air supply to less than 10 litres/minute to avoid any damage to the Gas Sensor.
Ice in your nitrogen supply - empty the dewar vessel and let it warm up to room temperature. Mop up any moisture in the bottom. Check on the purity of your liquid nitrogen by shining a flashlight into the dewar. The liquid should look clean like water but do not worry if you see a few particles in the bottom, this is fairly normal. If your liquid nitrogen is milky, you have a chronic contamination of ice, Cryostream can not handle this so talk to your liquid nitrogen supplier. Try to avoid pushing the rigid leg of Cryostream into the bottom of the dewar, this prevents this prevents particles in the bottom of the dewar being sucked up the leg.
An inward leak - Check to make sure all the nylon tubing is pushed 15-16mm into each quick-fit connector then perform the Nitrogen Circuit Gas Leak Test and inform Oxford Cryosystems or your local agent of your findings. Do not rush into changing a diaphragm as opening up the gas pump can often cause a leak. Speak to Oxford Cryosystems first.
Once the ice contamination problem has been rectified, fit an Oxford Cryosystems Line Drier Unit. If there is already one in circuit, it will now be contaminated and will require reactivation (see instructions). DO NOT fit a new one or a reactivated one until you have rectified the ice contamination. You will create unnecessary work and confusion for yourself.
Controller Status reads 'Ice Block warning will trip at 2 l/min'
If the Cryostream has shut down after a period of time during which the gas temperature has risen steadily and the Heat% has read zero, there is a good chance the vacuum is deteriorating.
When Cryostream experiences recondensation of nitrogen in its heat exchanger the liquid will spit down the nozzle and hit the Gas Heater and Gas Sensor causing the temperature to jump around as it reacts to keep the temperature stable, (this instability may cause the shutdown after a period of time.) This will also be associated with a fluctuation in the Heater power (Heat%). This unbalance in the heat exchangers can be caused by an outward gas leak or an Evaporator Heater set too low.
It is worth considering these solutions in order:
Condensation and/or ice covering the outside of the blue Coldhead or the flexible transfer line
Spitting of liquid nitrogen from the nozzle
Cryostream Shutdown due to large temperature error with unusually high or low GasT
Cryostream Shutdown due to large temperature error when refilling the dewar
Cryostream maintains an error of a few degrees that disappears when the dewar is topped up
If the Cryostream has shutdown due to a large gas temperature error and either the error or gas temperatures are nonsense values, (eg 30K or 600K,) the system is suffering from electrical noise. Possible sources of electrical noise are a Rotating Anode generator, noisy mains supply or static electricity.
Often moving a large (100-200 litre) storage dewar across a lab on rubber wheels can cause enough static to build up when the transfer hose it stuck in the opening of the dewar. Be sure to earth the nitrogen storage dewar before placing the transfer hose into the dewar used by the Cryostream.
If the problem persists, contact Oxford Cryosystems or your local agent.
Cryostream Shutdown due to large temperature error
The Cryostream Gas Heater is either open circuit (>64 ohms) or short circuit (<30 ohms). This can be caused by corrosion or contamination from particles or liquids in the lab or letting the dewar frequently run dry.
Make sure the Cryostream nozzle is not angled at less than 20 from the horizontal. This will prevent condensable from attacking the Gas Heater when the system is switched off.
Make sure there is always, at least, 5 inches of liquid nitrogen in the bottom of the dewar.
Contact your local agent or Oxford Cryosystems to arrange of the component to be repaired.
The Cryostream Gas Sensor is a very delicate silicon diode positioned just inside the end of the nozzle. If an object such as a pen, mounting pin or goniometer arc is inserted into the nozzle, this can cause damage to the sensor. Very much like the Gas Heater, damage to the Gas Sensor can be caused by corrosion from particles or liquids in the lab.
Warn all users not to push anything up the nozzle. Take extra care when placing and removing Tophats / Caps from the goniometer. No maintenance should take place via the nozzle exit.
Make sure the Cryostream nozzle is not angled at less than 20 from the horizontal. This will prevent condensable from attacking the Gas Heater when the system is switched off.
Contact your local agent or Oxford Cryosystems to arrange of the component to be repaired.
As these components are secured tightly inside the blue body of the Coldhead, it is very rare for them to get damaged. The most likely cause of damage to these components is from an electrical surge.
Contact Oxford Cryosystems or your local agent immediately. Do not try to service this yourself as there are no user serviceable parts inside the Coldhead.
Although sounds are often difficult to interpret it is worth noting a few things. The noise from the gas pumps vary from pump to pump and voltage to voltage. If you are unhappy with the noise your pump is making, possible causes are:
Contact your local agent or Oxford Cryosystems to get the replacement part or the pump serviced.
Wait for the Cryostream Coldhead to reach room temperature. This will usually require leaving the system overnight. Once the inside of the Coldhead has warmed up, remove the leg from the liquid nitrogen and allow that to also warm up (15-20 minutes.) These precautions prevent atmospheric moisture from contaminating the inside of Cryostream.
Disconnect the nylon tubes from the FLOW and SUCT Quick Fit Connectors on the top of the Coldhead flange.
If you are using a Line Drier Unit, remove it from the gas flow circuit. (If you do not remove it, you will contaminate it with atmospheric moisture. Leaving the Line Drier in the circuit, will smooth the flowmeter reading.)
Disconnect the two mains cables from the back of the controller. (If you are using a 500 series Cryostream, disconnect the mains cable from the back of the controller and the cable from the back of the Gas Box.) Run the gas pump directly from the mains by connecting the two cables together.
Your gas flowrate should read 5 litres / minute on your flowmeter. The top edge of the float should touch the bottom of the number '6' on the float.
While the gas pump is running directly from the mains, place your finger over the tube taken from the SUCT connector on the Coldhead. If the flow does not fall slowly to zero, you have an inward leak.
While the gas pump is running directly from the mains, place your finger over the tube taken from the FLOW connector on the Coldhead. If the flow does not fall to zero, you have an OUTWARD leak. If you are not using a Line Drier the float may bobble around at the bottom of the flowmeter, this is expected.
To be sure the flow rate of the outer dry air stream is correct, it is often better to set the flow by eye rather that by trying the guess what the flow should be by looking at the numbers.
Turn all the lights off in the x-ray room and shine a flashlight up toward the nozzle of Cryostream in an attempt to highlight the plume created by the cold gas stream. As the gas stream leaves the nozzle it is really made up of two parts; the first 'invisible' 10 or 12 mm and the remaining plume of ice. The object of the excerise is to maximise the length of the 'invisible' section. This should only be done over the first 15 litres / minute of air from the dry air source. One should not be fooled into thinking that at 25 litres / minute there is no plume, therefore, no ice because the ice will build rapidly around the end of the nozzle and blow the sample from its support.
For a variety of reasons, it is quite common for small quantities of water vapour to contaminate the nitrogen gas stream flowing through the Cryostream Cooler. If sufficient water is present an ice blockage will form which can reduce the flowrate or cause a "Low Flow" trip - this process may take a few days or several weeks depending on water vapour content.
The block forms in the FLOW path of Cryostream as the nitrogen gas is cooled from room temperature to liquid nitrogen temperature in the heat exchanger. Two possible sources of water vapour are ice in the liquid nitrogen or an inward leak in the SUCT or SUCTION paths of the gas circuit usually resulting from a badly nested Quick Fit Connector.
A third source is a split diaphragm in the gas pump but this is not likely to happen until the gas pump has run for approximately 10,000 hours.
When you first receive your Cryostream Cooler, RUN YOUR SYSTEM WITHOUT FITTING YOUR LINE DRIER. If there are any inward leaks or a high level of ice in the liquid nitrogen, Cryostream will block in a few days but, will not contaminate your Line Drier with water.
If this occurs, recheck all your Quick Fit Connectors (pressing them in 15-16mm,) check your liquid nitrogen and dewar then rerun your system. Cryostream should run for AT LEAST 7 to 10 days before a block occurs, altough poor quality nitrogen can reduce this to 2-3 days. (You will probably get an ice block warning within two or three days, this will appear on the STATUS line - 600 series Cryostream only.) Do not worry if you do not see any of these signs, you probably have very good quality liquid nitrogen.
Once you are happy that you can run for about a week, fit your Line Drier.
The Line Drier is designed to remove TRACES OF WATER VAPOUR from the nitrogen stream before an ice block can form. IT WILL NOT COPE WITH GROSS CONTAMINATION of the nitrogen supply or a large inward leak.
Check that all the nylon tubes are pushed fully (approx 15mm) into the Quick Fit Connectors. Also warm up and clean out the liquid nitrogen vessel at regular intervals, keep the vessel neck covered to prevent atmospheric moisture and 'rubbish' getting into the dewar. Also ensure the liquid nitrogen is of high purity.
Remove the plastic Blanking Plugs, (these plugs must be fitted to the Line Drier during transit and storage.) Fit the Line Drier in the DEL pipework between the Gas Pump and the Controller, (or Gas Box - 500 series Cryostream.) DO NOT LEAVE THE LINE DRIER OPEN TO THE ATMOSPHERE, THIS WILL AVOID CONTAMINATION.
Eventually the Line Drier will become saturated by water and require regenerating.
To regenerate, disconnect the Line Drier and unscrew the Metal End Fittings to avoid heat damage to the rubber 'O' ring seals.
Arrange to pass a flow of clean dry nitrogen (or any other inert) gas at about 1 to 2 litres/minute through the Line Drier from OUT to IN whilst heating the Line Drier to 200-250°C. DO NOT USE DRY AIR FROM THE DRY AIR UNIT. THIS GAS IS NOT DRY ENOUGH.
After 4 hours switch off the supply of heat, but allow the gas flow to continue until the Line Drier is cool (approx 2 hours). Replace the Metal End Fittings and Blanking Plugs immediately.
The easiest method of regeneration is to wrap the Line Drier in
a short Heating Tape / Strip (1.5 metres, 240 watts). Inject the
purge gas through a short (300mm) length of stainless stell tube
to act as a heat break. Small leaks at the couplings do not matter.
Alternatively, an oven may be used, but it may prove difficult
to pass inert gas through the Line Drier.
February 1997