Electronics > Projects, Designs, and Technical Stuff

Servicing Stirling Crycocoolers

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adammunich:
Hello Forum,

I recently purchased pieces of an MWIR camera for my CO2 camera project, and it has a stirling-cycle cryocooler from Ricor.

I'm currently trying to understand how they service these cryo-coolers.

Best I can tell is that there is a plug on top that they would unscrew, fill the thing with UHP 200-250psi helium, then screw the plug back in using indium as a sealing gasket. I can't imagine any other reason why this plug would have its hex socket slightly deformed if it wasn't serviced before in this way.

It seems to me that it would be easier to just machine a new plug and leave a valve connected to it, but I guess I'll cross that bridge when comes to it, as supposedly, this one was last re-filled 3 years ago and might still be good for a while.

Still, I am interested in getting in touch with anyone who has experience with these sorts of cryocoolers.


coppercone2:
I want to know this too. I am guessing valves for helium are not so good. Would look at valve cross sections and seal it extra tight.

CatalinaWOW:
Not really an expert but my understanding is the that there are several reasons for the plug approach.

First, as is mentioned is the difficulty of sealing helium.  But also cost of valves that are almost as good as solid metal seal and size of such valves.

Gyro:
You would do well to look through the Thermal Imaging subforum. There are several threads relating to cyrocoolers. I believe Forum member Fraser has a good deal of experience with them.

You might want to relocate your thread (or ask a mod to do it for you) to that subforum.

LaserSteve:
You may find the screw is seated in a indium seal and is not a simple screw shape.  You'll also learn the need for "ultraclean" and baking the instrument to drive off water of any kind, vapor or adsorbed. Then pull a really good vacuum on it before filling, while still baking, with a "cold trapped" pump.

The tool used is called a "valve actuator" and the prices are astronomical.  If have access to a really really good lathe you can make them.

Otherwise a copper or nickle tube is used and it is "cold welded" shut. The only way any one would get my cold weld tool is to pry it from my cold dead hands.

I don't work on cryopumps, but I work on something that needs similar  ultra-hermetic sealing technology.

Note for newbies, the  pinch tool used for refrigeration is not a cold weld pinch tool. Cold Weld Pinch tools have carbide or tungsten jaws and usually but not always are hydraulically driven. Real tools seal with > then 20,000 PSI.
Dont waste your money on the "hope and solder closed" method.

Steve

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