Page 377 - Centrifugal Pumps 2E

342 Centrifugal Pumps: Design and Application

component interfaces by means of a shear force applied to a key (e.g.
driver shaft to driver half coupling hub; pump half coupling hub to pump
shaft; and pump shaft to impeller). The general practice is to use a square
key which has a height equal to one-fourth of the shaft diameter. (See
ANSI-B17.1). The length of the key is determined by the strength re-
quirements and the length of the hub. The strength of the key is evaluated
by calculating the bearing and shear stress, assuming that the forces are
uniformly distributed along the length of the key.

Example

7
For a pump with a 2 /s~in. diameter shaft at the coupling and a maxi-
mum horsepower of 1,580 at 3,560 RPM, determine the coupling key
size. Shaft material is 4140 and the coupling key is 316 stainless steel.

Solution

The mechanical properties of the key material are lower than that of
the shaft, so it will be adequate to only examine the key.
The torque to be transmitted from the driver is:

The force on the key is: