Clearances

The total allowable tolerance (worst case) can be estimated using interference fits in the Machinery handbook. However, for positive displacement blowers (i.e Roots) the amount of slip varies based on the amount of back pressure.

Hope this helps.

All these devices place a fluid or gas under pressure. They draw from a medium under lower pressure. As tolerances increase so does the amount of medium travel though these gaps from high pressure to low. So there is a lost of efficiency. Some tolerance need to be there. As the medium is compress heat is generated which cause the materials of the pump to expand. Which will reduce the tolerance.

Go here and read this article.

http://www.pipingdesigners.com/Training%20-%20section%202a.htm

I think that this article will not bring info midofnowhere wants.

There are some guidelines for the designer how close the devices can be put to each other.

Midofnowhere is interested in internal clearances for rotating equipment.

I am steam turbine engineer experienced in overhauls, repairs, etc - I am not a designer.

Based on my knowledge obtained during my job I can say that customer quite often is going to accept bigger clearances even if it affect machine efficiency.

OK, some internal leakages are in place when bigger clearances applied but they make the machine operation safer.

I got one owner's turbine supervisor who said to me:

"I can accept bigger clearance but if it is too small the rotor is going to be sent back to your workshop". (I supervised the rotor overhaul at that time).

So the message was clear. Usually OEM is the best source to get info about clearances but as this is not a racket since after some time you can realize that each OEM uses the same rules and the clearances are very similar.

I cannot give you the formula to calculate the gaps as I am not designer. Please think about thermal elongation of steel parts and minimal gap required between rotating and stationary parts

Better see the OEM manuals, overhauling/dismantling procedures and asembly/disassembly checklist. Different clearances have different implications. Sectional equipment drawings may also be helpful.