SME's
- Adam White, adamwh@slac.stanford.edu
- Cynthia Melendrez, cymel123@slac.stanford.edu
- Chris Koerber, ckoerber@slac.stanford.edu
Hazards and Mitigations
- Asphyxiation
- Oxygen deficiency monitors (ODM) are required to be around dewar
- DO NOT ride with this on the elevators and use caution tapes inside the elevator
- Don't do work in small confined areas, areas must be approved to have a dewar in it
- Burns and fost bite
- Wear proper cryogenic PPE
- Keep heating gun around at all times.
- Do not touch frosted items without gloves!
- When inserting items into the dewar go slow! It needs to cool down or else it will boil.
- Heat valves with heat gun as needed to operate them.
- Crushing
- Wear steel toe shoes when moving the dewar.
- Do not tip dewar
- Pressure
- Vent the system in safe manner before doing work on the dewar
PPE
- closed toe shoes
- long pants
- cryo gloves
- face shield
- a cryo apron (can be a hazard on the ladder)
Equipment
- He dewar bubbler (optional if there is a scale)
- It is a long ~8ft section of 3/8" SS pipe with a dropper squeezer on the end. On the bubblier are two zip ties or clamps to help tell volume
- Scale
- 9/16 open ended wrench
- 2x adjustable wrenches
- Balloon grade helium
- All PPE called out above
- Heater Gun
- Ladder
- Measuring tape
Procedure
You and one other person review the
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various valves on the stinger and helium dewar
"T" Manifold
- On the stinger in the
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- dewar, spin the needle valve counterclockwise to close the valve.
- Turn off the roughing pump that is hooked up to the cryohead.
- Close the cylinder that is hooked up to the dewar and isolate it.
- Close all valves on the dewar. You will not be able to close the vertical one because the stinger is in it.
- Vent the poly line
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- that connects the dewar to the helium cylinder and undo the swage fitting on the the dewar side of the poly line.
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- Wearing gloves and a face shield, open the low pressure relief vent valve to vent out the
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- oolage of the dewar
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- . Keep this open for the remainder of the procedure. Verify that the pressure is dropping on the dewar's gauge.
- Keep an eye out for the PRV to freeze over. Use the heat gun to warm up
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- it up so the pressure relief device
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- doesn't freezing open.
- Once the pressure is ~ 1 psi in the dewar, start
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- to unscrew the seal that holds the singer into the dewar. You may have to wiggle it a bit.
- Take off the "T" manifold on the horzontal vent valve off, break behind the 1/2" SS NPT female thread.
- Deploy a ladder right next to the dewar
- Both people need to wear all PPE called out above
- One person will climb the ladder and the other stands near the dewar
- The person on the ladder will grab the braided hose and near the valves. They will start to lift up while the person below keeps them lifting straight up and wiggling the stinger. Only touch it with gloves.
- Once
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- it is fully out of the dewar close the vertical valve.
- You may have to pass it back an forth in order for them to climb down the ladder and rest it on a safe place. Be sure not to bump anything.
- Remove the ladder.
- Start up the vacuum pump that is connected on the cryo head and make sure the needle valve is fully closed on the stinger.
- Start to heat up the whole stinger with the heating gun for about 10 mins then focus on the very end near the stinger's three holes.
- Put the stinger in a safe place. (In xpp you can put it on the SB3's granite) Continue to let the roughing pump work on the stinger.
- If you care to see how much Helium is left and it's not on the scale follow this procedure: Liquid Helium Dewar Dipping (Testing How Full It Is)
- Undo the ratcheting straps that tie down the dewar.
- With two of you, remove it from the scale if it is on it, then roll up to the loading dock.
- Remove the ODM
Putting a new dewar in service, start from here (stinger is already in cryostat):
- Bring a new dewar down to the hutch that needs the replacement. Do not ride on the elevator with it!
- Put a the ODM onto the dewar, don't put it right in front of a PRV.
- Teflon tape the horizontal vent valve with the NPT fitting.
- Screw on the "T" manifold and firmly tighten it.
- Roll the dewar into position, if you need to place it on a scale use two people. Be sure to point the "T" manifold in such a way that won't hinder or spay people as the pass by.
- Take off the black cap on the vertical vent valve (keep it nearby) and snip the ziptie on the Low Pressure Relief Valve
- Rip off the "full" tag
- Strap the dewar down with a speed strap.
- Note down dewar's weight.
- Deploy a ladder nearby the dewar so one person could easily reach ~ 6ft over the top of it.
- Both people put on all PPE.
- Open the vertical vent valve.
- Grab the stinger and allow one person to climb the ladder then hand the stinger to them.
- With both of you, guide the stinger into the vertical valve all the way to the bottom. Go slowly as the helium will boil off and the pressure will rise. Try not to stand in front of the PRVs and keep the low pressure PRV closed unless you can stand off to the side of it.
- Once it is as far as it goes start to close the sealing gasket on the stinger. You may have to wiggle it to get the threads to spin.
- Note down the dewars weight if on a scale.
