THIRD REPORT OF THE EXPERIMENTAL RESEARCH ON DISC VALVE

Abstract

The present report relates to the third experiments made on disc valves with water. The arrangement of the apparatus was nearly the same as those discribed in the second report. The water from a supply tank, Fig. 42,A, flowed, through a 6-inch cast iron pipe of about 20 feet long, into a valve chamber of 4 inches diameter, Fig. 42,B, in which the valves to be tested were fitted. The difference of the level between the two overflow surfaces of the supply tank and the funnel above the valve chamber was nearly 4・85 feet. The pressure heads at several points on the valve chamber wall were measured by mercury manometers. The effective head or the loss of head due to the valve was found in the case of the smaller valves to be about from 4・85 to 4・75 feet. The lifting forces of water acting on the valve were determined by loading the valve with dead weight until it was brought into equilibrium states. The discharges of water through the valve were determined by means of a smaller tank mounted on a steel yard balance, and two larger calibrated measuring tanks. i. Tests have been made to determine the effect of width of the seat face. For this purpose three flat-seated valves were taken which have the diameters of 1 1/4,1 1/2 and 1 3/4 inches respectively, Fig. 1. The diameter of the port was 1 1/4 inches and the space around the valve could be altered by inserting cylindrical bushes of several diameters of from 1 7/8 to 3 inches into the chamber, Fig. 44. The results of the experiments are given in Tables 1,2,3 and Figs. 2,3,4,5. From these we learn that in the case of valve No. 9 (1 3/4 inches in diameter) the pressure drop due to the contraction of stream in the narrow passage on the seat face caused the greatest effect on the lifting force. (see the first and second reports) ii. In valve No. 8 (1 1/4 inch in diameter) the width of the valve seat was naught ; therefore, it might be expected that its characteristics would be of the simplest one. But it was not the case. The behaviors of the curves for lifting force much depend on the space left between the valve and the wall of the cylindrical bushes. Then with this valve the author attempted to determine the pure water pressure on the front face of the valve, and designed, as shown in Fig. 6,a special cylinder fitted with a long piston of 1 1/4 inches in diameter. To the bottom of the latter the valve was attached by means of small screws. The water pressure in the cylinder was measured by a manometer connected to the cylinder by means of a rubber tube. The curves plotted from the results of experiments, Fig. 7 and 8,show that the water pressure on the front face of valve No. 8 diminishes gradually as the valve opening increases. Next the piston was detached from the valve and was fixed to the cylinder by means of a set screw, so as a space of 0・6 inch was left between its bottom face and the back face of the valve resting on the seat. In this case the lifting force increases very rapidly as the valve lifts. We see from the results that the eddy current in the back space of the valve has considerable bearing on the characteristics of disc valve. Figs. 9 (b) and (c) show the arrangements for determining the total pressure on the front face of valves Nos. 6 and 7,one with flat seat and the other with conical seat, both having the diameters of 1 1/2 inches. The results of the experiments are shown in Figs. 10-13. We see in this case also the stream behaves in very complicated manners while flowing through the space between the cylinder and chamber wall. iii. With the object of studying the state of pressure distribution on the valve faces, valve No. 4 was prepared which was made hollow and had several piezometer holes bored on the faces, Fig. 17. A. A rubber tube was connected at one end to the top of the hollow spindle of the valve, and at the other end to a mercury manometer. The diameter of the valve was 2 1/2 inches and of the port 1 1/2 inches and of the chamber 4 inches. The