15 August 2002
flow main pumps, the pump elevations shall be about 0.9144 m (3 ft) below the drydock
Priming. All graving dock pumps not set at an elevation at which the
impeller is submerged at all times must be equipped for priming. Priming consists of
flooding the pump suction piping and the pump casing surrounding the impeller by
removing air by means of a vacuum pump.
Heating and Ventilating
. Provide heating and ventilation
pumproom, as required to prevent damage by moisture condensation and freezing, and
for the comfort of the operating personnel.
FIELD TESTING OF DEWATERING SYSTEM. In order to check the
operating characteristics with design requirements, it is necessary to field test the
dewatering pumps, including the hydraulic system as installed. These tests cover pump
capacity, power consumption, and evaluation of efficiency. For the results of an actual
field test, see Figure 7-2.
Determination of Capacity. Prepare a volumetric curve on which the
volume of water in the graving dock, in cubic feet, is plotted against elevations referred
to the datum plane, or to some other fixed elevation such as the graving dock floor or
coping. When appreciable leakage occurs, a leakage curve is prepared by recording
the rate at which water in the dock rises at various elevations.
Curve Construction. During pumping tests, the water elevations in the
dock are usually taken at intervals of 10 minutes. To the amounts of water pumped, as
determined from these observations, add the appropriate amount of leakage taken from
the leakage curves. The average capacity is the total amount of water pumped, divided
by the pumping time. Take water level readings in the dock with great accuracy,
preferably at two or more points simultaneously, and average. Use specially
constructed gages for obtaining accurate readings, unaffected by waves. To eliminate
inaccuracies in observations, plot all readings to large scale, draw a smooth curve, and
make any necessary corrections.
Power Input. Take readings, simultaneously with those for capacity, of
the power input to motors, as determined by calibrated wattmeters placed in the circuit
as near as practicable to the main switchboard panels. In computing results, make
corrections for ratio, scale, and phase-angle error. Determine frequency from speeds
taken on a synchronous motor feeding from the same source of supply as the pump
motors. Read pump speeds with a speed counter and stop watch directly from the
Determination of Head. Efficiency requirements may be based on total
dynamic head as determined by calibrated gages in the suction and discharge of each
pump, but variable results are obtained by this method. Tests based on static heads
between the levels of the water in the dock and the sea are more reliable than gage
tests, and give a more practical indication of the performance of the plant as a whole.