0
$\begingroup$

I am interested in building an experimental lubricant-less pneumatic tube system in which the canister will be propelled up to a high-velocity, reaching a peak velocity of approximately 100 m/s before the canister is forced to slow down and come to a stop.

The canister should attain a high velocity within the pneumatic tube by being propelled by ambient air pressure behind it and there being very low air pressure in front of it inside the tube (similar to the Hyperloop). I plan to create this very low air pressure either through the use of a vacuum pump, or perhaps by sealing one end of the tube with tape and then pulling the canister backward through the entire tube and then releasing it.

I have spent time researching on the Internet for what would be an ideal material to use for the O-rings that will wrap around this canister. The challenge I'm facing is trying to find O-rings that will keep the ambient air pressure from leaking around the canister and getting into the tube, and at the same time being slippery enough to glide over the tube's internal surface, whether the tube is made out of metal or PVC.

I have the option of putting standard rubber O-rings around the canister, yet this would require me to lubricate the pneumatic tube with some type of grease/oil before each test and I don't wish to lubricate several hundred feet of tubing for each test.

I have considered making the felt-covered, rubber O-rings, yet I think a lot of air may push through the felt. I have also considered making O-rings out of tightly wound silk, yet I think silk O-rings will not last very long. So, I am seeking suggestions on what would be an ideal material to use for these special-purpose O-rings.

What would be an ideal material to use for O-rings on a canister in a lubricant-less, high-velocity pneumatic tube system?

$\endgroup$
4
  • 1
    $\begingroup$ try the fuzzy half of a velcro strip (aka: loop side) ... you can get velcro in self-stick strips ... you can buy the strips separately (separate hook and loop sides) at a shop that sells sewing products $\endgroup$
    – jsotola
    Feb 2, 2023 at 22:48
  • 1
    $\begingroup$ you could try using a leaf blower as a pump $\endgroup$
    – jsotola
    Feb 2, 2023 at 22:53
  • $\begingroup$ @jsotola, that’s an interesting idea. I’ll have to find some Velcro and see how it it moves over a PVC pipe that I have. $\endgroup$
    – user57467
    Feb 2, 2023 at 23:15
  • $\begingroup$ duckduckgo.com/?q=retail+air+tube&iax=images&ia=images $\endgroup$
    – jsotola
    Feb 3, 2023 at 1:55

1 Answer 1

1
$\begingroup$

Precise machining of metals can result in a cylinder/piston fit so tight that it cannot be inserted if the exit hole is blocked. This would be impractical, in my opinion, in your application, as temperature is likely to be a factor over any appreciable distance.

Directly related to this, however is the concept of using a slippery material such as UHMWPE (Ultra High Molecular Weight PolyEthylene) as the casing. This will reduce the overall friction of the assembly.

For sealing, PTFE O-rings are available. PTFE is related to Teflon™ and is quite slippery as well. It's possible you may find a custom "not-O" ring with a flange that will seal against the tubing (lip seal) when under pressure, akin to a one-way flapper valve, but even a conventional O-ring will be more slippery than rubber compounds.

$\endgroup$
2
  • $\begingroup$ Thanks for these suggestions. I am going to do research on UHMWPE and PTFE O-rings. $\endgroup$
    – user57467
    Feb 2, 2023 at 23:20
  • $\begingroup$ @user57467 Also research lip seals. Since you are using ambient pressure, the pressure is limited to 14.7psi which is pretty low. You really don't need an o-ring for this and a lip seal will have much lower friction. Try Googling "ptfe lip seal" $\endgroup$
    – Eric S
    Feb 3, 2023 at 0:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.