Some interesting information on Ricor Cryocooler (K526S) Refill Device

[MrSheep]

I came across this interesting page which describes a custom fixture device for servicing a broken Ricor K526S Cryocooler. As I suspected it is a device that clamps the cryocooler down so it doesn't fly off while refilling under high pressure. The site contains 3D Models that can be rotated for better viewing. This is the first i've seen of an actual model of such device :0

https://m-labs.hk/software/solvespace/

[MrSheep]

Oh wow even better, while searching for Ricor K526S I found this GitHub page containing the fixture device and its 3D Files for creating such device . Maybe I can finally find a way to self service my cryocoolers.

https://github.com/whitequark/ricor-k526s/tree/master

[Fraser]

MrSheep,

A great find and it matches my understanding of how such a unit is constructed 

I suppose it all comes down to creating an assembly to rigidly hold gas seals in place during the fill process and permit the operation of a “screwdriver” to seal the fill port at completion. There appears to be a single fill port on the assembly so presumably the cooler is first evacuated with a vacuum pump, then the various hoses and valves somehow flushed and purged of impurities with UHP Helium, then the cooler filled using the pressure regulated UHP Helium fill process. It sounds relatively straight forward but I found the required parts to be expensive in the UK. Anyone who already owns the vacuum pump, gas gauges, regulator and Lab grade Helium gas bottle fitting can do the task far more cheaply of course. Alas I do not think I can justify the cost of building such a setup. If you do succeed in this quest to refill cryo coolers, I will be very interested  to hear about your experiences building and using the fill rig. 

Fraser

[MrSheep]

Yeah this was the final piece of the puzzle. I have a general understanding of the plumbing involved. Basically it is a bunch of swagelok tubing, fittings and valves connected to both a vacuum pump and a UHP tank. Each having valves respectively for the vacuum and refill cycles.

I already have the vacuum pumps and as for the UPH, while a bit on the expensive side, isn't too hard to get. And yes for sure, I will share my progress on here if I ever do decide to build this device. It is for one very interesting to me and it will keep my cameras going for years to come.

[MrSheep]

Also I wonder what type of seal they use. Not sure if it is viton seals. I do recall orange looking seals for the cryocooler itself. Not sure what they are called but they are prob designed to withstand the pressures involved to contain the helium.

Circled in the attached image are where the seals are probably meant to be.

I will probably 3D print this later today, just for fun and have it as a desk model. As well as have a better way to visualize the device.

[Fraser]

Helpful O-Ring seal information……

https://www.marcorubber.com/high-pressure-o-rings.htm

[Fraser]

An issue I have with the presented design is the coolers fill hole sealing screw tool. In the shown design there will be the Helium gas fill pressure acting upon that tool, pushing it like a piston to its rearmost position. How is this “piston” pushed down the cylinder to engage the screw seal with the mating seal face and soft seal in the cooler ? It has to be pushed to engage the seal screw in the mating thread and rotated to move down the fill hole threads. There is surely a mechanical way to do this but I would have expected a fill gas bleed-off to the rear of the “piston” to equalise the pressure differential across it. The external shaft that turns the seal screw tool would obviously need to be adequately sealed as well.

Fraser

[MrSheep]

That is a great question. I think they used a retaining washer of some sort as described in the first link:

"Then, a fixture was designed, shown below with a cutout (blue). It consists of a bracket, a piston case that screws into the bracket (the thread is not modelled), a piston with a retaining screw, a retaining washer, a Swagelok fitting attached to the orange port (not modelled), and a few compression gaskets (also not modelled). The bracket and the piston case hold the cryocooler The retaining washer prevents the piston from being ejected by high pressure helium and, conversely, together with another washer prevents the piston from being sucked in and blocking the gas flow during evacuation."

How that is implemented is another mystery that needs solving.

[Fraser]

I can see how the “piston” is retained in the cylinder as there is a plate screwed to the rear of the cylinder. What I am unsure about is whether a person can place a driver through the hole in that rear retaining plate and actually push the whole piston forward to engage the screwdriver part in the coolers fill port. From memory the Helium fill is at 200psi. I would have expected a bleed of the 200psi Helium to be passed to to rear end of the “piston” to enable easier movement of the “piston”. A sealing strategy would be needed for the rear of the cylinder behind the “piston” of course otherwise the balancing helium from the bleed path would be lost to atmosphere.

[MrSheep]

Yeah that makes sense. Wonder if someone can chime in on this.

[MrSheep]

After some thought and research, I think what is needed for this tool is a "Rod Seal"

https://ahpseals.com/rod-seals/

It looks like they can withstand high pressures. Here is a tutorial on hydraulic seals. This is prob the same concept for what I am trying to achieve:



Also to hold the rod seals a groove will have to be cut within a cylinder. Wondering if I should attempt this since I have a CNC or use a service for it.
Apparently you can mill a groove using a special tool:

[MrSheep]

Wow I went down a rabbit hole. Was researching some Sofradir detectors and ended up finding this channel who so happen to have the mysterious refill devices for both Ricor and Thales cryocoolers. This is the first time I've seen such device.

[MrSheep]

Attached looks like the Fill/Purge adapter. Notice how there is no fixture. Just a turntable knob. After some thought I think I finally understand how this works
Basically the turnable knob is attached to a hex key/driver. And there is a threaded cylinder in the shape of a Y. with a quick disconnect. This quick disconnect leads to the helium line of the machine. The machine is capable of pulling high vacuum on the cooler and periodically purging and filling helium to get rid of any contamination. Then finally it gets filled to the desired pressure of usually 20-35bar.

You might ask yourself how do you refill such device without removing the hex set screw. Then that really got me thinking. And I came up with the conclusion that you don't need to remove the set screw entirely , I was always under the assumption that you needed to remove it when filling. I believe when the set screw is loosened the gap between the screw and bore is large enough to let helium/vacuum in and out. This is probably why there is an indium seal at the bottom of the screw! So even if the tool and the set screw have the same thread diameter it doesn't matter since loosening the plug is all you need and set screw removal is not necessary.

  Maybe one of these days I will draft up something in fusion and perform some tests.