Page 94 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

Installation, Maintenance, and Repair of Vertical Pumps 79

An alternate method to set semi-open impellers is:

1. Raise the rotor as high as it will go, then lower it two turns on the
adjusting nut. While raising the rotor, do not use excessive force.
Especially if the impellers are collet mounted, be sure that they are
not pushed downward. Just raise the rotor until a very slight drag is
detected when the shaft is rotated.

2. Lock the adjusting nut, start the pump, record the ammeter reading
with the pump running at or near shutoff or at the minimum flow
allowed by the system.

3. Check to be sure that the ammeter reading is less than the amps on
the motor nameplate.

4. Lower the rotor 1/12 turn, lock the adjusting nut, start the pump,
record the ammeter reading with the pump running at or near shut-
off or at the minimum flow allowed by the system.

5. Repeat Step 4 until the ammeter reading increases sharply because
the impellers are rubbing on the bowls.

6. Raise the rotor 1/12 turn to its final position and lock the adjusting
nut.

Hollow Shaft Driver Reverse Protection Clutch
If the driver is accidentally run with reverse rotation, the deepwell
pump shaft couplings may unscrew and cause damage. Figure 2-9 shows
a reverse protection clutch which automatically disengages the pump
shaft from the driver if this occurs. In some shallow settings, particularly
with closed impellers, the pump may develop a momentary upthrust dur-
ing start-up. In these installations, it is necessary to install hold-down
bolts in the clutch and to check that the driver thrust bearing is locked
against upthrust.
Hollow Shaft Driver Nonreverse Ratchet

If the foot valve or check valve fails in a deepwell pump installation,
when the driver is de-energized the water will run back down the dis-
charge column, and the pump will act as an unloaded turbine and achieve
a reverse rotation that can reach rather high speed. The torque does not
reverse, so the threaded couplings do not unscrew as a result. Although