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	Run/Service Summary



	Misc. Procedures



	Troubleshooting

Pumping the cooling tube

The cooling tube maintains a high vacuum in its dewar in order to provide a low cold flow of nitrogen gas. However, the vaccum in the dewar can become bad along with time. One option to recover the vacuum is to send the tube back to MSC. They can repair the vacuum and keep it for a year or longer. But this is fairly costly and time consuming with a turn-around time of about two months. An alternative is to use the pump in the lab to do it yourself. You can certainly pump the vacuum to the same level as that of MSC, but it won't last that long. However, you can pump it whenever you have to, even when you are collecting data and even without taking it out of the tank.

Usually, the pump, through a high vacuum tubing, is already connected to a VO-8 adaptor that fits the other end to the cooling tube. Also, a vacuum gauge is hooked up to monitor the vacuum. Then, just do the following:

1. Connect the VO-8 adaptor to the cryo tube's vacuum seal (at the turn of the cryo tube). Tighten the adaptor (you'll need a big spanner) so that it clamps on the tip of the tube firmly. This is very important; otherwise, you won't get a good vacuum because large leak may result from the connecting.

2. Push the knob of the VO-8 adaptor all the way in. When you do so, feel how it engages with the seal in the cryo tube and you can actually tell when the threaded stick head of the knob touches the threaded hole on the seal. Then turn the knob clockwise until you can't turn freely.

3. Now, turn on the vacuum pump. Let it pump the high vacuum rubber hose connected to the adaptor. Watch the vacuum gauge. In a matter of a minute or so, the vacuum should reach 0.06 torr or better; otherwise you may have a problem with the connection between the adaptor and the tube. If so, rework the connection.

4. At this point, pull out the knob with a reasonable force. This opens the seal and starts pumping the dewar. The final vacuum can reach down to 0.03 torr in a few minutes. It's actually okay as long as you reach 0.05 torr, which is already good enough for reaching -179^oC at a flow rate of 40 shown on the flow gauge on the control station. Just leave the pump on for as long as you are taking data.

5. When you are done with your data collection, don't shut down the pump immediately. Turn off the control station and leave on the vacuum pump (not the pump for running the cooling system!). In a couple of hours, come back check the tube temperature (just turn on the control station for a couple of seconds). If it's reached the room temperature, then follow the reversed steps to turn off the whole system. Most importantly: close the vacuum seal of the cryo tube first and then turn off the pump.

Common Procedures
	Filling Up Tank
	Cooling
	Pumping Tube
	Purging Tube
	Changing Heater
	Aligning Nozzle

Common Problems
	Can't Fill Up
	Cooling Temp. High
	LN From Nozzle
	Tube Sweating
	Power Trip

Resources

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