Bearing oil flow requirement calculation.

[dbecker]

Hello,

I was asked to compute oil flow requirements for journal bearings for a power turbine. There are three bearings, two journal and one thrust, all fluid film. Shaft diameter is 12" and speed is 3600 RPM. That puts the surface speed at about 188 ft/s.

I went to the kingsbury website and used their pdf on flow vs. shaft speed and computed about 41 GPM for all three bearings.

I just recieved information for more experienced folk that this number sounds way to low and should be in the realm of 250-300 GPM.

This is the document I used.

http://www.kingsbury.com/pdf/catalog-leg.pdf

Go to page 9 for thrust bearing oil requirement and page 33 for journal bearing calcs.

If anyone has input, it would be great.

Thank you,

- D

 

[clay87]

Only 2 journal bearings and 1 thrust bearing? Driven equipment has its own lubrication? 250-300 GPM sounds high.

 

[dwvns]

Hi,

Using the English Electric/GEC bearing flow rate standard "rule of thumb" equation, (regrettably I have been unable to find a reliable reference for this equation; it is emprical):
Q = 0.00208*D^3*RPM*(c/D)
assuming that your bearings have a clearance ratio (c/D) of approx. 0.0016, then
Q = 0.00208*1728*3600*0.0016 = 20.7 gal/min per bearing.
Excluding the thrust bearing this indicates flow of 41.4Gal/min.

I've previously found this equation to be reasonably reliable with maybe 15% scatter, this agrees fairly well with your calculation, and certainly 250-300GPM is an incredibly huge amount, out of all proportion with the bearings you're describing. Perhaps your colleagues are thinking of litres/min, but even then it's a somewhat high estimate.

You did not mention whether you are using US or imperial gallons. My calculation, above, is based on imperial gallons, ie. 4.543 litres.

Regards,
Dai

 

[Tmoose]

maybe the 250 gpm is gph ?