THE WOOD PROPELLER PUMP.
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.
Fig. 457.
Fig. 457.
For example, if one runner at a given speed, gives 10 pounds pressure per square inch, then two runners would give 20pounds; 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.
Fig. 458.
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.