Page 157 - Centrifugal Pumps Design and Application

Vertical Pumps 135

checked for correct rotation before being connected to the pump.
Threaded couplings torqued in the reverse direction will unscrew, and the
resulting jacking motion may cause serious damage. However, reverse
rotation from backflow through the impellers will not cause the cou-
plings to unscrew because the direction of shaft torque remains the same
as for normal operation.
For column shafts four inches and larger in diameter, a keyed sleeve
coupling should be used for transmitting torque. Axial thrust should be
carried through split rings retained by thrust collars. Flanged bearings,
both in the column and the bowl assembly, are recommended for bores
four inches and larger.

Shaft Enclosing Tube

When abrasives or corrosive properties prohibit the pumped liquid
from being used for flushing and lubricating the column bearings, the
bearings should be fitted inside a shaft enclosing tube. The bearings, typ-
ically of bronze material, are threaded on the O.D. and serve as joiners
for the five-feet long enclosing tube sections. Bearing alignment is pro-
vided by placing the enclosing tube assembly in tension through a
threaded tensioning device located in the discharge head. The enclosing
tube is stabilized within the outer column by random placement of hard
rubber spiders, the hub of which fits tightly around the enclosing tube
and the three legs fit tightly against the inside of the outer column. The
desired bearing lubrication, which can be oil, grease, clean water, or any
fluid compatible with the pumped liquid, is injected at the top end of the
enclosing tube assembly.
To overcome the mounting number of assembly and handling problems
that can occur with increase in column size, an enclosing tube integrally
welded with ribs at the top and bottom of the outer column is a preferred
design. Alignment is assured with simultaneous machining of the regis-
tered column fits, the inner column joints, with slip fit and "O"-rings,
and the bearing seats. Furthermore, the need for a tensioning device in
the discharge head is eliminated. The result is that both assembly and dis-
assembly time for the pump is significantly reduced.

The Head Assembly

The discharge head is designed to serve the following functions:

• Support the suspended, liquid-filled weight of the pumping unit.
• Provide support for the driver.