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Rotary Seal 1

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Eltron

Eltron

Mechanical
Mar 3, 2005
2,459
I'm looking for a shaft seal that I'm afraid doesn't exist. Let me run you through my particulars. I'm designing a housing that must hold 100PSIG clean air. I have a single 25mm shaft running through the drive side. This shaft spins at ~14,000rpm. Since I am designing the housing, I have (almost) no geometric constraints (within reason). I understand that this is a high PV for a shaft seal, but I was hoping someone here would have a magic bullet for me. Any suggestions? SKF has something that gets kind of close, but still not quite there. I can decrease the rpm by as much as 1/2 if necessary, but I'd rather not.

Dan

Dan's Blog
 
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Eltron,
You are considering standard wet seals that cannot achieve such a high PV however you can consider seals that are specifically designed for gas applications and high PV. Consider using seals with spiral grooves that achieve hydrodynamic lift and operate as non contacting seals. These seals are used in many applications specifically in gas compression and cryogenics. You may be familiar with Sundyne (or Sunstrand) pumps or compressors. These units have similar shaft diametes and operate at this speed and higher you should contact a local John Crane representative to see if these seals can be adapted to your application. If these are not suited then I am sure a seal can be designed using standard components. Estimate leakage rates can be provided to see if these are suited to your application. When using these seals I assume that your application is DOL and that you will not have VSD. If you spin these seals slow and depending on the speed you may not achieve hydrodynamic lift and result in face contact damaging the seals.

A labyrinth will not hold these pressures without excessive leakage at this pressure.

You can search the net under Dry Gas Seals so you better understand the principle operation of these seals.

Good Luck!
 
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Hi!

Yes, that's true. Labyrinth seals tend to get some leakage. This should be known in order to evaluate the permisible leakage on eachy case.

Also, I forgot about "gry gas seals" proposed by flexibox /thx). Flowserve* also has a range of dry gas seals.

Since these are, basically, laser made, I think (because this is not my field) many mechanical seals manufacturers can have their own style (even Flexibox?).

You have different styles, mainly, depending on the sealing/rotation needed. Unidirectional (the one flexibox shown), or bi-directional. The way of working is similar to labyrinth seals, althougth this one is more like a mechanical seal.


*I hope not to break any rules giving names

 
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Yeah, I'm pretty sure the labyrinth seals are out since I can't tolerate leakage in this test stand. I am indeed varying the speed on the drive motor as well so the seals that require hydrodynamic lift my get damaged during startup operations which take ~3-4min.

Dan

Dan's Blog
 
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Do not count them out until you have it checked out as they can run contacting for periods providing that is within their limit. Another option if a single seal cannot accommodate the slow speed, intall a dual pressurised Dry Gas seal then providing you pressurise the seal at all times it overcomes the slow speed issue.

Good Luck! Keep us posted with final decision.
 
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I ended up going with the Flexilip seal from Parker (LDN profile). Bit of a long lead time, but she works like a beaut. Dieselmax, if you're interested in how they work I'd consult the Parker Seals Handbook available on their website.

Thanks again for the input, guys.

Dan

Dan's Blog
 
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Hi, Eltron

Sorry about this message... but I have serious doubts that this seal will do the job.

Nevertheless, as always, Triblogy is unpredictable.

As soon as this kind of seals is my job, we tried to use one of these on a similar application, and the final result was damaged axes!

Just bear on mind that pressure is very high, also than speed, so you'll be working with a seal on maximum values. You need to use a good cooling for the lips (i.e. using grease between lips)

It also depends on axe hardness and seal material. Regarding seal material, I can offer you my advise if you let me know wich one is it the one they proposed.


 
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