Shaft seal suppliers in the UK

[picclock]

I'm trying to find a supplier of shaft seals in the UK. The shaft size is 10mm and will rotate with a surface speed of 100fpm/30M per minute/0.5m per Sec. In my experience thay all seem to use different criteria.  The pressure differential is up to a max of 200 psi, and the temperature range is ambient or just above, say max 40C to a minimum - 10C (depending on the weather). 

I've got some mechanical seals which will do the job, but I'm a bit pushed for space. As this is only a 'project' type application it would be good to find a stockist of some sort.

I do have a bodgeit backup plan. I have the remains of an electric failed car tyre inflation pump which allegedly worked to 220psi. I figure I could drill a hole through the piston and fit to the shaft with an oring seal. Then I could shorten the 'barrel' (just a piece of steel tube) and fit that to the stationary part. The pressure rating would be good and the speed per second would be below its original design, and the temperatures cooler.

However I'd much prefer a 'real' part if available at a reasonable cost in the UK.

Any help much appreciated

Best Regards

picclock

[Lew_Merrick_PE]

Just Google "Rotary Shaft Seals UK" and you will find half-a-dozen suppliers on the first page.  I normally deal with a Seattle-area (US, Washington State) supplier, so I can't vouch for any of those listed.  The biggest hassle is dealing with minimum order amounts, but they are usually not too bad when it comes to this type of product.

[picclock]

Hi Lew

Already done that - this post was a bit of a last resort  .

I know that in the US these things are a phone call away. I emailed 4 of the Uk suppliers, only 1 replied with an offer to sell me seals that were not rated for the pressure at a mere £50 + VAT + Shipping. Its just not easy this side of the pond. I've also found some info on google for using O'Rings as a dynamic shaft seal. I figured it would be easy (and cheap and available) to try it to see if it lives up to the claims. The info states up to 800psi and  600 fpm which is way in excess of my needs. Link also gives interesting info on floating Oring piston seals.


http://www.rlhudson.com/O-Ring%20Book/designing-dynamic.html


On shaft tolerances - the guides seem to indicate 5 thou max gap which doesn't seem correct to me. When the seal is not pressurised 1/4 of the seal diameter is not touching the shaft or housing (ingnoring pre squeeze). As pressure is applied the oring deforms to make the seal. At 200 psi my 2mm oring will experience a force of 7 pounds which will decrease its presquashed radius to a 0.7mm curve. This means that the size of the low pressure quadrant will shrink to 24 thou. This implies that the shaft clearance could be much larger without detriment to the seal.  See attached drawing. Shaded area is low pressure, shaft is red, housing blue. These are from actual measurements I made with a 2mm oring, and whilst not that accurate clearly illustrate the point that any part of the housing within 24 thou of the shaft does nothing. Obviously, one assumes the shaft is properly supported with bearings, and that the quadrant above the shaded one will equalise with the high pressure.


Best Regards

Picclock

[Lew_Merrick_PE]

Hey Picclock,

I would be loath to suggest an o-ring for this application.  I was a member of the team that wrote the o-ring section for the 1976 edition of SAE's Automotive Engineering Handbook.  (You can see my resurrection of this now "lost knowledge" at http://www.scribd.com/Lew%20Merrick.)  I would consider a labyrinth seal as seeming more appropriate to your description (30,000 rpm).  An axial clearance in the .040/.030 range should be sufficient and a diametral clearance in the .010/.005 range (at temperature) with 3 full "blanks" ought to get you there.  I would (speaking through my hat as I do not know the details of your application) make the shaft side a one-piece, press on detail and the housing side a two-piece clamshell attach assembly.  Given your rather low delta-P (200 psi), I would consider using a round-plate-with-hole stress analysis to set the thickness to (say) nominal to yield at 450 psi.  (Roarke's Formulae for Stress & Strain would be the most common source, but I prefer Blake's Practical Stress Analysis.)

Once the air inside the labyrinth goes turbulent, you will have very little leakage.  ???

[picclock]

Hi Lew

Interesting stuff. My little shaft will rotate at a maximum of 1000 rpm and experience a maximum differential pressure of 200 psi. Just ambient temperatures and a shaft diameter of 6-10 mm. If it leaks a bit its not catastrophic but it would be nice to have somthing that works reasonably well. I plan to use an oil bath on the high pressure side of the seal for lubrication. 

Typical pressures and speeds will be half of that. Even considered using stuffing. Not really sure how effective labyrinth seals would be at the lower speed end - most likely good enough.

It's interesting to note that the design info on the site listed in my previous post only lists 3 diameters of orings and indicates the optimum one with minimum squeeze is 3.5mm. Not sure what that's about.

Thanks for the info. I didn't really consider a labyrinth seal as they leak when static, and I don't know how well they will work at low speeds - but if I can't get on with the oring design I'll give it a try. A big plus point with them is that they don't have seal faces to wear.

Many Thanks

picclock

 


 

[Lew_Merrick_PE]

Hey Picclock,

I thought that the "30K" reference in your original post was the shaft speed.  At 1000 rpm a bronze bushing with .002/.001 clearance that is at least 1.5*shaft_diameter long ought to give you a good seal.  A shoulder (clamp ring) on either side of the bushing (1 touching, the other a couple of thou clearance) should finish the seal nicely.

???