Labyrinth Seal (Tolerance per inch of shaft for oil seal)

Look at AFM (actually AFMUSA).

I'll check that out,, thanks for the info

Are you talkikng about a lip seal or a laby for keeping oil in the bearing? Or are you talking about shaft end seals? (To keep gas in the case) or break down bushings as part of an oil or gas seal arrangement?

Depends on the arrangement, could be as little as 0.5 mil per inch, up to 2 or 3 mils per inch of shaft diameter.

I'm thinking it would be the seal from a separate motor shaft leading to a semi-hermetic compressor.

I am sorry, but I am still not getting which seal you are talking about. What exactly is the machine train? Sounds like maybe a refrigeration compressor? Some sort of chiller package perhaps?

There are seals that keep bearing oil out of the motor, and there are seals that keep gas in the compressor. Which ones are you refering to?

Well Steve S.---

I don't have any specs on the equipment the question was geared for. I'm thinking my instructor wanted me to the grasp the concept behind the seal which I now do.

As far as "Tolerance" is concerned, that is a general question and will be specific to each piece of equipment--- so perhaps it's a rule of thumb thing which I'm quickly finding out does not mesh well with anything "engineering"

thank you for your reply

BTW-cool blog you have there,,, My uncle went to the same kind of school and is now a professor with 5 books to his name.

OH! ok. I thought you were working on a specific problem with a specific machine. My apologies for being so slow on the uptake.

The labyrinth radial clearance is relative to the bearing clearance, usually labyrinth seals are used on sleeve bearings, you may find the maximum clearance for the bearing is a useful number for labyrinth clearance.

The shaft clearance in a sleeve bearing, the number 0.002 inch per inch of shaft diameter is stuck in my head, from working around large, slow shafts and sleeve bearings 25 years ago. The shaft speed and lube oil used, any contaminants that cause oil foaming and pressure / vacuum can create problems for labyrinth seals.

The labyrinth will also have a end-float clearance based upon the shaft length from the thrust bearing, this length can grow with thrust bearing end float and with shaft length change due to temperature. The thrust bearing may actually be in another machine and have a (flexible) coupling limiting the end float?

Dan

Thanks Dan---

At this rate I'll need to head to Costco for more printer paper---so many good responses so little paper.

I'm making up sets of binders with all of this great info I've been getting that way I'll have something to use as a field reference manual once I start plying my new trade.

Thanks Dan..I am joining in between.

I need info about flexible coupling limiting the end float. My customers are always asking about this when we offer couplings with our fans. Can you give some idea?

Best Regards,

D.Saravanan

I maybe wrong on my opinion. However, to be careful with the shaft tolerance i may have to go by the OEM drawing for safe or to a seal manufacturer (if it is supplied with the seal itself) for recommended tolerance of the shaft.

Jojie

This thread is all mixed up. Some Basics:

Labyrinth seals ARE NOT used for oil seals--they are used for GAS sealing.

Labyrinth seal 'clearance' is not usually related to shaft diameter, but shaft END FLOAT

Labyrinth seal 'overlap' (how much the static blades extend past the rotating blades) is one of the two ctitical dimensions, the other is blade clearance side to side.

Sleeve bearing clearance is typically 0.0005 to 0.001" per inch of shaft diameter, depending on speed, precision of fit, and operating temp vs room temp.

Throttling bushings with 'seal oil' are typically used to reduce case pressure to near atmospheric prior to a radial lip seal on the shaft.