The following is an example of how a lift adjustment can improve the performance of a Service Water Pump at CNS.

The "C" Service Water pump is a single stage, vertical mixed flow pump manufactured by the Byron Jackson Pump Company. The pump is a model 28 KxL VC, rated at 8000 gpm. Its driver is a three-phase, synchronous motor rated at 300 horsepower, 1180 rpm, and 4160 v with a power factor of 87%. The nominal impeller diameter is 28 inches.

On July 13, 2000, a surveillance of Service Water Pump "C" was made. When such a surveillance is done, the pump flow is throttled to 5500 gpm and the pump is run by itself within the division, as opposed to being run in tandem with another similarly sized pump in the same division.

In that surveillance, it was reported that the pump was performing poorly. The Total Developed Head was found to be 133.6 ft, and the differential pressure (TDH converted to psig) of the pump was found to be 57.7 psig. Since the lowest acceptable differential pressure for this pump is 57.1 psig and the lowest acceptable Total Developed Head is 130 ft, Service Water Pump "C" was in jeopardy of being declared inoperable, especially since a scheduled overhaul was a year away.

Records indicate that the pump last had a lift adjustment on April 5, 2000, when the water temperature was about 52^oF. The river temperature was about 75 ^oF on July 13, 2000. The differential expansion due to this change in temperature is about 34 mils. This amount alone would have increased the pump lift to about 85 mils, which is not acceptable for efficient performance. Impeller and bowl wear, and any "settlement" would add even more. Thus, it was expected, that the impeller clearance had opened too much by July 13, 2000, and that this was the cause of the poor performance.

Table 2 lists the performance data of the "C" pump as it was measured on July 13, 2000.

Plugging the above data into equation (viii), gives the following.

h(I_rms)(V_rms)(1.732)(PF) - L_clearance = [P₁/r + Q²/(A²)(2g_c) + Z][dm/dt]

h(161,500 ft lbf/sec) - L_clearance = [(6768 lbf/ft²) /(62.27 lbf/ft³)

+ (12.25 ft³/sec)²/(2.07 ft²)²(2)(32.17 ft/sec²) + 25 ft][ 763.0 lbf/sec]

h(161,500 ft lbf/sec) - L_clearance = [108.7 ft + 0.54 ft + 25 ft][ 763.0 lbf/sec]

h(211.7 ft) – [L_clearance]/[ 763.0 lbf/sec] = 134.2 ft

Since previous experience with this pump indicates that the overall efficiency of the motor and pump is 64.85%, then from the data gathered on July 13, 2000, the losses associated with the clearance in this case were about 3.1 ft of head. This accounts for a loss of output pressure of about 1.33 psig.

From the above data and analysis, and assuming that the same operating conditions continue to exist, an increase of 1.33 psig in the differential pressure could be obtained if the lift were adjusted. If the 1.33 psig amount were added to the 57.7 psig figure, which was obtained in the surveillance, it would give a DP of 59.0 psig. This would take the pump out of jeopardy.

On July 22, 2000, a lift adjustment on the same pump was made. Prior to the adjustment, the existing clearance was found to be 128 mils, which is 68 mils larger than the upper limit for lift settings noted in CNS Procedure 7.2.45. After the lift adjustment was made, the "as-left" clearance was measured at 51 mils, which is very close to the manufacturer’s recommended value, and well within the range of values listed in CNS Procedure 7.2.45. Table 3 lists the performance parameters of the pump after the lift adjustment was made and another surveillance was run.

PF = 0.87 (given)

Plugging the above data into equation (viii), gives the following.

h(I_rms)(V_rms)(1.732)(PF) - L_clearance = [P₁/r + Q²/(A²)(2g_c) + Z][dm/dt]

h(169,640 ft lbf/sec) - L_clearance = [(7344 lbf/ft²) /(62.22 lbf/ft³)

+ (12.25 ft³/sec)²/(2.07 ft²)²(2)(32.17 ft/sec²) + 25.8 ft][ 762.36 lbf/sec]

h(169,640 ft lbf/sec) - L_clearance = [118.0 ft + 0.54 ft + 25.8 ft][ 762.36 lbf/sec]

h(222.9 ft) – [L_clearance]/[ 762.36 lbf/sec] = 144.3 ft

Assuming that the overall pump and motor efficiency had not changed in the interim, then the clearance losses after the lift are estimated as follows.

(0.6485)(222.9 ft) – [L_clearance]/[ 762.36 lbf/sec] = 144.3 ft

144.56 - L_clearance = 144.3 ft

Thus, the lift adjustment done on July 22, 2000, removed the losses occurring in the pump due to excessive lift clearance. It also increased the Total Developed Head of the pump from the previous value of 134.2 to 144.3 ft. This improvement placed the pump well above the 130 ft minimum head requirement.

The improved TDH after the lift adjustment converts to a differential pressure of 62 psig. This is apparently much better than the 59 psig DP figure which was predicted from the pre-lift data. The apparent variance between the two figures is attributed to instrumentation error.

The error in reading the pressure gage is +/- 1 psi. The error in reading the ammeter is +/- 1 ampere. The error in reading the voltmeter is +/- 10 volts. The error in reading the river level is about +/- 1 inch, and the error in reading the flow is about +/- 100 gpm.

Based upon these tolerances, the error in determining the electrical energy input is about 6%. Similarly, the error in determining the energy output of the pump is about 5%. Thus, the improved DP of 62 psig as measured by the second surveillance is within the error range associated with the predicted 59 psig DP figure.