Page 96 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

Installation, Maintenance, and Repair of Wm'cal Pumps 81

the reverse speed may be higher than normal pump rpm, it seldom causes
damage unless water-lubricated column bearings are run dry, or an at-
tempt is made to restart the driver while the pump is running backward.
Hollow shaft drivers are often provided with nonreverse ratchets so that
reverse rotation does not occur. Alternatively, some systems have time-
delay relays to prevent premature restart. For deepwell pumps with set-
tings of 500 ft or more, the long shaft may act as a torsional spring caus-
ing the nonreverse ratchet to be subject to torque reversals. This problem is
controlled by providing a ratchet which is designed so that the movement
caused by torque reversal is only 3 to 5".

Driver Allgnment
Practically all vertical pumps now used in process plants within the
United States utilize the driver thrust bearing to carry the combined
thrust load of the driver and pump. The driver also provides radial align-
ment for the upper portion of the pump shaft. Reliability of the driver
bearings is a prerequisite to the reliability of the pump. Accurate radial
and angular alignment between the driver and the pump is therefore es-
sential. Driver shaft runout and concentricity with the mounting fit must
be checked prior to assembly or reassembly of the driver on the pump.
Referring to Figure 2-10, the following steps are recommended:

1. Thoroughly clean the driver shaft and mounting face.
2. Attach a dial indicator to the shaft and rotate on the driver rabbet fit
and mounting face.

a. The concentricity of the rabbet fit must be within .002 in. total
indicator reading (T.I.R.) per ft of rabbet fit diameter.
b. The mounting face must be perpendicular to the shaft within
.002 in. T.I.R. per ft of rabbet fit diameter.

3. Mount the dial indicator on the driver housing to check the shaft
runout and end float.
a. The shaft runout must not exceed .002 in. T.I.R. or .001 in.
T.I.R. per in. of shaft diameter, whichever is greater.
b. The squareness of the split ring groove to the shaft centerline
must be within .002 in. T.I.R.
c. Shaft end float must not exceed .010 in. T.I.R., and .005 in.
T.I.R. is preferred if the pump has a mechanical seal.
These requirements are more stringent than NEMA standards but are
essential for solid shaft drivers, particularly for pumps operating at 3600