The pump shown herewith lifts the water by propeller screws or
“runners,” each consisting of two half-circular inclined blades
fastened to a shaft at intervals of 3 to 5 feet, and of slightly less
diameter than the casing, so as to revolve freely within it.
Experiments have demonstrated that more water can be raised with a
given speed by putting the runners close together near the bottom of
the pump.
A bearing for the shaft is placed immediately underneath each of the
runners, and held in position by a set of spring “guides” attached
lengthwise to the well-casing. These guides interrupt the whirling
motion of the water as it is thrown upward by the runners, and turns
it back in the opposite direction, thereby delivering it into the
revolving runners in a direction opposite their motion. By this method
the whirling motion of the water is utilized and the capacity of the
pump largely increased without a proportional increase of power to run
it.
With this pump, water may be raised from several hundred feet below the
surface by extending the shaft and runners down the well-casing to the
desired depth; it being always necessary to submerge the lower runner.
As the shaft rotates the lower runner lifts the water up to the runner
above it, and so on to the next, until the water is delivered at or
above the ground if desired; the distance depending upon the size and
pitch of the runner, the number of runners, and the speed at which they
are driven.
Speed is not increased for additional depth, because more runners are
added, and this compounding of the runners increases the efficiency of
the pump.
A ball bearing is placed over the stuffing-box to carry the entire
weight of all the movable parts of the pump, and also the column of
water. In deep wells cone roller bearings are used in place of the ball
bearings.
The pumps are made to fit all sizes of wells and of any desired
capacity. Runners of various pitches are made for the different sizes
in order to suit the supply of water or the power available. If, after
testing, the supply of water in the well is found to be limited,
the runners are changed to raise the amount of water due to a given
horse-power, then runners can be furnished with a pitch suited to
lifting that particular amount of water.
[Illustration: FIG. 457.]
For example, if one runner at a given speed, gives 10 pounds pressure
per square inch, then two runners would give 20 pounds; three, 30
pounds, and so on. For this reason water may be elevated higher above
the discharge with this pump than with a centrifugal, for it would
require a higher rate of speed to lift a given amount of water 20
feet with one runner, than to lift the same amount 5 feet. Hence the
advantage of compounding the runners as the lift is increased. The
compounding of runners is one of the main features of success and
efficiency of this pump.
[Illustration: FIG. 458.]
Where the water is beyond the suction limit this pump can be used to
raise the water to the surface, discharging into the suction of the
force pump. In this manner, whatever surplus of power the propeller
pump might have in raising the water to the surface, would be utilized
in helping the water through the force pump.
The speed of rotary pumps is generally high, ranging from 800
revolutions per minute for the small sizes to 250 revolutions for
the larger sizes. In a number of experiments made upon this form of
pump the highest efficiency was obtained with pressures ranging from
30 to 50 pounds per square inch, and speeds ranging from 475 to 575
revolutions per minute. The average efficiency of the rotary pump is
from 48 to 52 per cent.