Cleaning a "clogged" porous graphite air bearing?

Hoping someone here has some experience with porous graphite. I've seen lots of posts about people trying to make their own air bearings using porous graphite, but nothing about maintaining or cleaning them, so here goes:

I've been using a set of porous graphite air bearings sourced with CO2 (using bottles and a regulator from paintball parts)to build a fully self-contained floating platform to be used for satellite propulsion testing and attitude control testing. Using CO2 has not been a problem and the platform has worked very well for this purpose.

The other week, I was checking the platform for leaks by spraying soap water around the fittings and checking for bubbles--while the system was turned on. I failed to remember that the CO2 bottles have an anti-siphon tube in them to prevent liquid CO2 from entering the rest of the system, and the regulator began to freeze up and the whole system stopped working.

I was able to replace all the damage components in the regulator and it works good as new now, but the air bearings are acting as if they're "clogged". Prior to this, I was able to run the whole thing at about 30 PSI, but now I have to crank it up to 60 PSI and it still doesn't float as effortlessly as it used to. I'm trying to figure out what could have caused this but I don't know enough about how porous carbon interacts with soap, water, or liquid CO2.

I would imagine that any liquid CO2 would boil off quickly and escape as a gas. And if soap were to somehow bind to the microporous structure of the graphite, wouldn't a quick dunk in water wash it away? I've tested the bearings to confirm them still work by submerging them in a bucket of tap water and observing bubbles emerge from them, and I've rinsed them with isopropyl alcohol to displace the water, but they're still acting funky.

If anyone here has some experience with this, I would greatly appreciate any suggestions you have.

Interesting application! If the bearings are reasonably robust (you can handle them and they don't crumble) they might survive ultrasonic cleaning. Use a water or water/isopropyl mix to start, and only for short periods until you confirm they aren't being damaged by the process.

Once clean, you can try baking them (with a slow ramp up in temp to prevent remaining water from boiling) to clear the pores.

This is just spitballing, try at your own risk. But whatever you find that actually works please let us know.

Just a thought, being that regulator was on the fritz, any chance your psi readings were erroneous before, and now that reg has been fixed it is correct? Cannot see how C02 would clog the pores?

You were spraying soap water on the outside of a regulator and CO2 pressure tubing, and the cooling effect of the CO2 vaporizing froze the water to the outside of the system? I'm not seeing how this would affect anything inside the system.

I'f I'm understanding this, the only two things I can thing of are that soap got into the bearing and is clogging it. If that's it, run distilled water through the thing backwards if you can.

If the freezing soap water somehow knackered the graphite pores, I think you need new bearings.

If any of the liquid CO2 made it to the air bearing it could well have caused damage to the microstructure. Crumbled carbon due to the damage could very easily have clogged the bearing - as I recall the pores are pretty damned fine in these - I'm wanting to say submicron. Anything at all getting into the line could cause restriction - and it's sounding like that's your problem if it requires higher pressure to achieve the same flotation. I don't think you will get them unclogged. Time for new bearings most likely.

Apologies for the delay, but thank you for all of your inputs!

Since I posted this, I've gotten the bearings to work *marginally* better than before. I did the following three actions prior to retesting:

1) Rebuilt the superstructure using 3D printed materials. Prior to this, I was using a heavier 1/4" thick Aluminum plate approx. 12" square and a brass manifold (since I'm sourcing the CO2 from two bottles into one regulator). I replaced the manifold with a single brass tee coupled with some push-to-connect fittings, and I replaced the Aluminum structure with a plastic 3D printed structure that holds the bearings in place and supports the weight of the pneumatics. All told, i reduced the weight by about 40% (from ~4kg to 2.4kg).

2) Per the suggestion of New Way's customer support, I cleaned the bearings with 70% isopropyl alcohol. To do this, I submerged the bearing in the IPA and applied a reverse pressure using a syringe to try and draw the IPA backward through the porous media in the hopes of dislodging any debris and drawing it out the back. This process is sloooooow so I rigged the syringe to stay drawn-out and contuously apply the negative pressure to the bearing over the course of a few hours.

3) Cleaned the table with IPA and lint-free cloth. Which should have been obvious, but we normally leave our table covered to prevent debris and dust from getting on it in the first place. At any rate, doing a quick wipe-down prior to every run seems to help.


I'm writing this as I run the bearings through an ultrasonic bath to see if I can squeeze out any more performance. As of this writing, I was able to get decent performance ("decent" meaning I can gently push the unit and watch it come to a stop approx. 3ft away -- still need to quantify how much force I'm applying to get an idea of the friction factor) by running the regulator at 60 psi.

I'm beginning to suspect it might have less to do with my supply pressure and more to do with my flow rate. I can get up to 100psi without any problem, but the tubing and connectors are very small diameter (the reg. output is a #10-32 hole connecting to 5/32" OD tubing) so the flow might be choking. More investigation will be required.

This sounds to me like you may need an air table. You might talk to Alvey Conveyor, 9301 Olive Blvd. St. Louis, MO 63132 316-993-4700

One of my classmates worked there but he is long retired so I don't have a contact.

There are all sorts of air hockey tables available.

Bill