dynamic rotating surface seal help

[jrkeme]

OK I'll try to keep this brief.
I have an application that is meant to diminish (not seal) leakage from a 50-100psi vessel around a 5 inch rotating disc out an orifice. So within the pressure vessel is a 1 inch rotating shaft with a 5 inch disc mounted to it. The disc at the moment is right up against the end cap housing. We tried to get a very small clearance but it still leaks too much. So this rotating disc that is right next to the end cap of the pressure vessel is rotating with 2 holes in it. As the holes rotate they uncover an orifice in the end cap (that is what they are supposed to do) However since we do not have sealing around the outside of the disc there ALWAYs a permanent leackage path to the orifice in the end cap. What we want is for higher pressure air to only go through the orifice when one of the two holes in the disc align. Not that PLUS the leakage around the disc.

SO! What I am looking for is not shaft sealing. What I would like to do is put an "o-ring" or equivalent around the perimeter of the disc so that when the disc is pushed up against the end cap (recall we tried to do 0.010") there is some type of sealing mechanism. So think of the disc as a hamburger with a 5 inch onion ring around the perimeter that is "compressed against the end cap. I am very ok with this NOT being a actual full seal. It can be a clearance seal that as the "material" wears due to "break in" the remaining gap is very tiny. This is my cave man view of what I think will work. ESPECIALLY Since what I would like does not seem to exist. Keep in mind I cannot easily put a "lip seal" around the circumference of the 5 inch disc against the radial part of the housing. That gap is greater than 1 inch.

Does something like this exist? To conclude I am expecting some leakage. Is there a consumable part/ring that I could install into the rotating disc that when pushed up against the end cap I get an effective seal to leakage around the outside of the disc. So really my onion ring is fully in contact with the end cap at all times. I was thinking of something made of PTFE or carbon?

Thanks everyone
Jason

 

[GregLocock]

RPM? Finish on shaft? Grease permitted? Expected life? You know, specs, in general?

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[jrkeme]

Thanks Greg
Shaft speed is about 1000rpm
Surface finish of the shaft does not matter. As I said above nothing is sealing against the shaft
There are millsions of shaft sealing solutions. This seal mush be on the perimeter to or edge of the 5 inch rotating disc that is pressed against the flat end cap
On the pressure vessel. Grease could be ok. It this unit is meant to run for many hours. 1000 hours or more. It last a durability test rig for components
Jason

 

[GregLocock]

Wade through this

https://www.parker.com/content/dam/Parker-com/Literature/Engineered-Polymer-Systems/5350.pdf

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[3DDave]

As long as you have two holes in the rotating plate you always have a leak path. Any tiny gap across the width of the disc results in a large area.

It requires flatness on the order of millionths of an inch per square inch to seal. That's how ceramic valves in kitchen and bath faucets work and at similar pressures with a far more viscous fluid. I expect a spring load is required to ensure a good contact regardless of runout with the shaft. Ceramic plates seem mostly to be available from China.

Other than that there are lip seals that would seal the perimeter, but that won't be enough. You'd need a groove for the seal to be embedded in and a very smooth 5-10 microinch surface to run against.

 

[MintJulep]

Generically what you describe is called a "face seal".

 

[jrkeme]

all thanks for the guidance. MintJulep. Thanks a ton for the phrasing. I was really struggling with what to call it. 3DDave vary astute on the leakage path! Yes the two rotating holes will also provide a leak path but by area cutting the perimeter area out would significantly reduce the overall leakage by in my case 75%.
I can easily put a groove in my rotating discs as we made them. No Problem. The surface finish they go up against itsn't bad. it is precision ground stainless steel. Probably not to the level you refer too but honestly. I am just looking for something BETTER than what I have now. I'm not trying to sell these things to NASA. I just want to durability test pneumatic valves by cycling pressures and right not I cannot get to my target pressures because of too much leakage. If I can cut it by 50% I might be ok.
Jason

 

[jrkeme]

 

[jrkeme]

this is a PPT image of what I was thinking but I think everyone who has responded understand the layout. I wrote PTFE as the seal but that was when I had no idea of the right technology.
The shaft is sealed on the other end with a PTFE seal from Garlock. Which is a normal shaft seal

 

[aldumoul]

Have you looked into using a contact seal?

 

[MintJulep]

Why?

There are many commodity options available for "cycling pressure", all of them cheap and most with no leakage at all.

Why are you wasting your time trying to bootstrap something complicated and kludgy that will never be even close to good?

 

[jrkeme]

Thank you aldumoul I will look into contact seals.

mintJulip. Cycle at 100x per second?
And also behave. You are not showing good forum etiquette. I’m making it because I want to make it

 

[MintJulep]

1000 rpm * 2 holes / 60 s/min = 33.3 Hz.

 

[jrkeme]

1000rpm would be acceptable for the test but the target is faster than that. I would be ok with 33Hz.

 

[MintJulep]

There are plenty (well, at least a few that I've found) solenoid valves that can operate at 100 Hz.

SMC makes some valves that can operate up to 1,200 Hz, but they're small, with small flow, so you'd need to find a fast relay valve too.

 

[EdStainless]

If the shaft and disc runout is very tight (<0.001") and the disc is very flat and very smooth then face seals will work fine.
If you don't have super precision on these parts then a face seal won't work.
If reaching the precision required is too difficult then look for other ways to vent and simply use a good shaft seal.
We used to vent test rigs through to two valve system.
One valve was set for continuous low flow and the other was modulated to give precise control.
Some hybrid system may work for you.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[jrkeme]

Thanks EdStainless. with this being an internal part to the pressure vessel it is very hard to get a good read on the runout. Right now I am close to reaching the pressures I need and that is without any sealing. Since face seals are relatively cheap and won't require a redesign it is worth it to try that solution first. If I can just boost the pressure by 10psi I might be ok

 

[Orange_kun]

You're looking at 6.6m/s surface speed for that seal near the OD, even at your lower stated speed. That's not nothing. You'll want to find something PTFE-based most likely, and be okay with it melting a bit. I'd be worried about the seal moving in the groove and generating even more heat.

Why is a solenoid out of consideration? Cost? Flow rate? 32Hz is easy.

 

[jrkeme]

Orange_kun
Thanks for the suggestion. I thought PTFE too. I am ok with it melting some. As i said I don't need complete sealing just better then nothing which is what I have now.

As far as solenoid. The system shown about has already been designed and constructed at a fairly large cost. So at the moment I am trying to get it working as is before I even considering scrapping it and going in a different direction. Also the current orifice opening is 1" in diameter so the solenoid would need to be that size and opening at about 100Hz. Right now the disc has 3 holes so 33Hz would be 100 opening events per second. (this is the target, not a hard requirement)

 

[MintJulep]

https://thedecisionlab.com/biases/the-sunk-cost-fallacy