Figs. 379-382.
The Pohle system of elevating liquids is shown in Fig. [377]. The process “consists in submerging a portion of an open-ended eduction-pipe in a body of the liquid to be raised and continuously introducing into the liquid within the lower part of the pipe a series of bubbles of compressed gaseous fluid containing enough of the fluid to expand immediately across the pipe and fill the same from side to side, forming pipe-fitting piston-like layers at or just above the point of their entrance into the pipe, whereby the column of liquid rising in the pipe after the forcing out of the liquid first standing in the latter is subdivided by the gaseous fluid into small portions before it reaches the level of the liquid outside of the pipe, and a continuously upward-flowing series of well-defined alternate layers of gaseous fluid and short layers of liquid is formed and forced up the pipe.”
The figures represent the apparatus in a state of action pumping water, the shaded sections within the eduction-pipe, W, representing water-layers and the intervening blank spaces air-layers.
At and before the beginning of pumping, the level of the water is the same outside and inside of the discharge-pipe, W,—incidentally, also, in the air pipe. Hence the vertical pressures per square inch are equal at the submerged end of the discharge pipe. When, therefore, compressed air is admitted into the air pipe, a, it must first expel the incidental standing water before air can enter the eduction-pipe, W. When this has been accomplished, the air-pressure is maintained until the water within the eduction-pipe has been forced out, which it will be in one unbroken column, free from air-bubbles.
When this has occurred the pressure of the air is lowered or its bulk diminished and adjusted to a pressure just sufficient to overcome the external water-pressure. It is thus adjusted for the performance of regular and uniform work, which will ensue with the inflowing air and water, which adjust themselves automatically in alternate layers or sections of definite lengths and weights. It will be seen in the figures that the lengths of the water-columns (shaded) and air (blank spaces) 1 and 1 are entered at the right of the discharge-pipe, W; also, that under the pressure of two layers of water 1 and 2, the length of the air column 2 is 6.71 feet long, and so on. The lengths of aggregate water columns and the air columns which they respectively compress are also entered on the right of the water-pipe.
On the left of the water-pipe are entered the pressures per square inch of these water columns or layers. Thus the pressure per square inch of column 1 is seen to be 1.74 pounds; that of 2, consisting of two columns or layers 1 and 2 each 4.02 feet long, to be 3.49 pounds, and that of 10, consisting of nine columns or layers of water 1 to 9, inclusive, each 4.02 feet long, and one of 3.80 feet in length (viz., layer 10) to be 17.35 pounds, and the aggregate length of the layers of water is 39.98 feet in a total length of ninety-one feet of pipe.
It will be noted that the length of pipe below the surface of the water in the well is 55.5 feet, and that the difference between this and the aggregate length of the water layers (39.98) is 15.52 feet—that is, on equal areas the pressure outside of the pipe is greater than the pressure on the inside by the weight due this difference of level, which is 47.65 pounds for the end of the discharge pipe.
It is this difference of 15.52 feet, acting as a head that supplies the water pipe, which puts the contents of the pipe in motion, and overcomes the resistance in the pipe. In general the water layers are equal each to each, and the pressure upon any layer of air is due to the number of water layers above it.