Shaft size estimation
Shaft size estimation
(OP)
Hi friends,
Is there any formula/thumb rule to estimate pump shaft size roughly?
Assuming we know flowrate and head of pump.
Thanks
Is there any formula/thumb rule to estimate pump shaft size roughly?
Assuming we know flowrate and head of pump.
Thanks





RE: Shaft size estimation
The way a practical engineer does it is he/she look in the pump catalog listing and find what the manufacturer picked as the shaft size. There is no better practical and horse-sensical method.
Unless you plan to be building pumps, why would you want to be able to calculate the best/optimum/desirable/practical/etc. shaft size? And if you don't know how to do it now, why go into pump fabrication? Manufacturers select their shaft size from practical/economical reasons. They can calculate the theoretical size that will do a given job, but then they have to consider other things: other impeller/hp uses of the same pump shaft, surges, contingencies, etc. This is the real side to engineering: the real life applications - of which there may be more than one.
RE: Shaft size estimation
Naresuan University
Phitsanulok
Thailand
RE: Shaft size estimation
RE: Shaft size estimation
To do the actual calculations, you need all the hydraulic characteristics of the pump, bearing dimensions, shaft dimensions, plus motor and drive details.
"If A equals success, then the formula is: A = X + Y + Z, X is work. Y is play. Z is keep your mouth shut."
-- by Albert Einstein
RE: Shaft size estimation
RE: Shaft size estimation
It comes from the basic cantilevered beam deflection formula, which you can find in any book on mechanics: y = F x L3 / (3 x E X I), where F is radial load, L is cantilevered length, E modulus of the elasticity of the material, and I is moment of inertia.
The lower L3D4, the less is shaft deflection, which is better for mechanical seal alignment, vibration and shaft whip. If L3D4 becomes too large, a pump shaft can snap, especially if operated close to shut-off, where hydraulic radial loads are excessive and not ballanced on volute type casings. ANSI pumps have L3D4 ratios range from 20 to 120, but newer designs have been introduced with this ratio below 10.0.
Regards Checman
RE: Shaft size estimation
Naresuan University
Phitsanulok
Thailand