Impeller Adjustment of the vertical turbine pump

• Proper impeller adjustment positions the impeller inside the bowl assembly for maximum performance.

• The impellers must be raised slightly to prevent dragging on the bowls.

Impellers are of two basic types: enclosed and semi-open (also referred to as semi-enclosed). The type and size of impeller, as well as the application, determine what the proper impeller adjustment must be. The type of impellers installed in the vertical turbine pump can be determined from the vertical turbine pump nameplate or packing slip. If the second letter of the vertical turbine pump type is K, it is an enclosed impeller and if the letter is O, then it is a semi-open impeller.

Hence DKM indicates enclosed impellers, while DOM indicates semi-open impellers (refer to Figure 5-6).

CAUTION：EQUIPMENT DAMAGE

The impellers must be completely down against the bowl seat when starting the impeller

adjustment. All dimensions and instructions given above are based on the assumption that

the impellers are seated. When pumps are subjected to suction pressure, the pressure

acting against the shaft tends to raise it. If the suction pressure is great enough it can raise

the shaft. Make sure the shaft is down when starting to adjust the impellers.

1. Enclosed Impellers: for proper impeller adjustment refer to the vertical turbine pump nameplate on the discharge head.

2. Semi-open Impellers: the adjustment of semi-open impellers is more critical than that of enclosed

impellers. A small change in the impeller setting impacts the vertical turbine pump performance considerably (refer to Figure 7-1 ).

Impeller Readjustment

Typically, impellers do not require readjustment if properly set at initial installation. Almost no change in performance can be obtained by minor adjustment of enclosed impellers; however, the positioning of semiopen impellers has a definite effect on the performance of the vertical turbine pump. This characteristic is sometimes used to adjust the output of the vertical turbine pump without valving. Figure 7-1 illustrates the general effect of raising semi-open impellers.

After extended operation, the sealing faces between the semi-open impellers and the bowl will wear causing a reduction in performance. the vertical turbine pump performance can be brought back up to almost “as new” by proper readjustment of the impellers. 

NOTICE：Adjusting the impellers will change the mechanical seal setting unless the seal is loosened

from the shaft. It is recommended to first loosen the seal from the shaft, perform the

impeller adjustment, then reset the mechanical seal.

Figure 7-1 indicates the approximate effect of raising semi-open impellers from their ideal (a) operating position. Raising the impellers increases the clearance between the impeller and the bowl seat and reduces the performance accordingly. The chart is generic and not exact for any particular pump model since each model reacts differently. 100% head and capacity are to be taken as the head and capacity of the vertical turbine pump at the best efficiency point.

If after making the below adjustment the vertical turbine pump does not deliver its rated capacity, the impellers can be lowered one step at a time until the lowest possible adjustment is achieved without the impellers dragging.

On the other hand, if the impellers appear to be dragging after the initial adjustment the unit must be stopped and the impellers raised one step. Dragging the impellers will increase the vertical turbine pump power considerably and can usually be heard and felt as increased vibration.

CAUTION：Excessively dragging impellers during operation will result in equipment damage. If

dragging occurs, stop the vertical turbine pump and increase the impeller setting.

If semi-open impellers are raised and then adjusted down, a slight increase in the power required will be noted due to the increased delivery of the vertical turbine pump. Do not confuse this with the marked power increase when impellers are lowered enough to drag.

• For optimum performance the impeller must run within a few thousandths of an inch of the bowl seat.

The exact shaft adjustment varies according to variables of each installation.

• For close coupled units, a general rule of 0.015" plus 0.005" of adjustment for each 100 feet of discharge head produced by the vertical turbine pump, plus 0.005" adjustment for each 10 feet of column assembly will provide close to ideal adjustment.

• Use the highest discharge head that the unit is expected to operate against to calculate the impeller adjustment value.

Impeller Adjustment - Hollow Shaft Driver

Impeller adjustment when using hollow shaft driver is accomplished at the top of the driver by the following procedure.

1. Remove the driver canopy.

2. Install the headshaft as outlined if not already in place.

3. Install the driver clutch as per the driver instruction manual and bolt into place.

4. Install the gib key, ensuring the top of the gib key pushes down below the top of the clutch. To prevent interference with the headshaft nut, fit the gib key to both the motor clutch and the headshaft. The key must slide in smoothly in the keyway.

5. Check the shaft position; the impellers must be fully seated against the bowls prior to adjusting the impellers.

6. Thread the headshaft nut down (right hand threads) until the impellers are lifted off their seat and the shaft rotates freely. When semi-open impellers are used, the correct determination of the point where the impellers just barely clear their seat is very important for proper adjustment.

7. Adjust the impellers as outlined.

8. Lock the headshaft nut with the lockscrew inserted down through the holes in the headshaft nut and threaded into the driver clutch.

CAUTION：DAMAGE TO the vertical turbine pump AND THE DRIVER

Always ensure the headshaft nut is locked before starting the driver to avoid damage to the vertical turbine pump and the driver.

Impeller Adjustment - Solid Shaft Driver (thrust bearing in driver)

Impeller adjustment when using a solid shaft driver (with thrust bearing in driver) is accomplished with the adjustable flanged coupling located below the driver.

Adjustable Flanged Couplings

1. Assemble the coupling on the vertical turbine pump and the driver as outlined.

2. Back off the adjusting nut up the shaft (threads are right hand) until the nut bears firmly against the spacer or driver shaft and the headshaft does not move down. This ensures that the impellers are all the way down against their seat and in proper position for starting the adjustment.

3. Thread the adjusting nut down until proper impeller adjustment as outlined can be measured between the adjusting nut and spacer or driver half coupling as shown in Figure 5-7.

4. Slide the vertical turbine pump half coupling up the shaft and align the adjusting nut bolt holes with those in the vertical turbine pump half coupling. Rotate the driver shaft until bolts can be inserted and tightened.

5. Tighten all the bolts. This will raise the impellers to correct operating position.

Impeller Adjustment - Solid Shaft Driver (thrust bearing in pump)

Impeller adjustment when using a solid shaft driver (with thrust bearing in pump) is accomplished using the adjusting nut located on top of the vertical turbine pump’s thrust bearing.

1. Install the thrust bearing drive key, ensuring the top of the key pushes down below the top of the thrust bearing clutch. To prevent interference with the adjusting nut, fit the key to both the clutch and the top lineshaft. The key must slide in smoothly in the keyway.

2. Check the shaft position; the impellers must be fully seated against the bowls prior to adjusting the impellers.

3. Thread the adjusting nut down (right hand threads) until the impellers are lifted off their seat and the shaft rotates freely. When semi-open impellers are used, the correct determination of the point where the impellers just barely clear their seat is very important for proper adjustment.

4. Adjust the impellers as outlined.

5. Lock the adjusting nut with the lockscrew(s) inserted down through the holes in the adjusting nut and threaded into the thrust bearing clutch. Use all lockscrews supplied.

CAUTION：DAMAGE TO the vertical turbine pump AND THE DRIVER

Always ensure the adjusting nut is locked before starting the driver to avoid damage to the vertical turbine pump and the driver.

6. After the impeller adjustment is completed, the flexible driver coupling may be installed.