OCR Text |
Show WELL DATA MEASUREMENT* 57 In determining the flow of water discharged through a pipe of uniform diameter all that is necessary is a foot rule, still air, and care in taking measurements. Two methods are proposed- one for pipes discharging vertically, which is particularly applicable before the well is permanently finished, and one for horizontal discharge, which is the most usual way of finishing a well. The table [ on page 58] is adapted to wells of moderate size, as well as to large wells. In case the well is of other diameter than given in the table its discharge can without much difficulty be obtained from the table by remembering that, other things being equal, the discharge varies as the square of the diameter of the pipe. If, fo.- example, the pipe is one- half inch in diameter its discharge will be one-fourth of that of a pipe 1 inch in diameter for a stream of the same height. In a similar manner the discharge of a pipe 8 inches in diameter can be obtained by multiplying the discharge of the 4- inch pipe by 4. In the first method the inside diameter of the pipe should first be measured, then the distance from the end of the pipe to the highest point of the dome of the water above in a strictly vertical direction- a to 6 in the diagram [ fig. 5]. Find these distances in table [ p. 58, A] and the corresponding figure will give the number of gallons discharged each minute. AVind would not interfere in this case so long as the measurements are taken vertically. The method for determining the discharge of horizontal pipes requires a little more care. First measure the diameter of the pipe, as before, then the vertical distance from the center of the opening of the pipe, or some convenient point corresponding to it on the side of the pipe, vertically downward 6 inches, a to b of the diagram, then from this point strictly horizontally to the center of the stream, b to e. FIG. 5.- Diagram illustrating flow from vertical and horizontal pipes. With these data the flow in gallons per minute can be obtained from table [ p. 58, B]. It will readily be seen that a slight error may make much difference in the discharge. Care must be taken to measure horizontally and also to the center of the stream. Because of this difficulty it is desirable to check the first determination by a second. For this purpose columns are given in the tables for corresponding measurements 12 inches below the center of the pipe. Of course the discharge from the same pipe should be the same in the two measurements of the same stream. Wind blowing either with or against the water may vitiate results to an indefinite amount. Therefore measurements should be taken while the air is still. Whenever fractions occur in the height or horizontal distance of the stream, the number of gallons can be obtained by apportioning the difference between the readings in the table for the nearest whole numbers, according to the size of the fraction. For example, if the distance from the top of the pipe to the top of the stream in the first case is 9J inches, one- third of the difference between the reading in the table for 9 and 10 inches must be added to the former t* o give the correct result. In case one measures the flow of a well by both methods he may think that the results should agree, but such is not the case. In the vertical discharge, there being less friction, the flow will be larger; so, also, in the second method differences will be found according to the length of the horizontal pipe used. As pipes are occasionally at an angle, it is well to know that the second method can be applied to them if the first measurement is taken strictly vertically from the center of the opening and the second measurement from that point parallel with the axis of the pipe to the center of the stream, as before. The measurements can then be read from the table. |