Testing the New Pumps of the St. Paul Water Works
Pumps of the St. Paul Water Works were tested at the shops of the builder before shipment. The pump efficiency exceeded 80 per cent, over quite a range. However, as the specifications were based on the overall efficiency, including the motors, the water department conducted a careful test after installation. The pressure gauge of each pump was taken off and calibrated on a dead weight testing inby meter. The recording instrument supplied with this meter includes an indicating dial, a recording card and an integrating counter, but, in order to verify the accuracy of its readings, an indicating mercury manometer was also connected to the pressure pipes of the tube. The electrical measuring instruments were checked and calibrated subsequently by comparison with standard instruments by representatives of the Northern States Power Company. In running the test, the head against which the pumps worked was controlled by means of a hydraulic gate valve on the discharge side of the pumps. After throttling the gate valve, no readings were taken until all instruments had ceased fluctuating, after which two or three readings were made and averaged, if any variations were found. Observations were made with the pumps operating under four different heads, covering a wide range of delivery. Centrifugal pump No. 25,650 with the connected electric motor showed a maximum overall efficiency of approximately 78.5 per cent, when operating against a head of 158 feet, while pump No. 25,651, with its motor, showed a maximum overall efficiency of 78 per cent, when operating against 143 feet.