conical and curved surfaces of the needle produced by the high-velocity flow whenever the valve is either partially or wholly opened. (b-2) Were this valve to be used in a pipe line or penstock, then (a) would be augmented by conduit pressure over the full area of the downstream conical and curved face of the needle. Closing forces. (c) Conduit pressure in chamber A against the convex upstream face of the movable needle head. (d) Conduit pressure in chamber C against the interior conical end curving surfaces of the discharge end of the needle. With conduit pressure in chambers A and C, closure can be effected with conduit pressure present in chamber B or with the pressure in this chamber reduced. With the forces produced by the above pressure combinations, the piston or needle may be moved to the opened or closed positions or to any intermediate position desired and maintained there indefinitely by regulating the exhaust from chambers A and C and from chamber B. This valve provides a larger effective opening force and a larger differential closing force over the opening force than any of the previous needle valves, due to the fixed diaphragm inside the needle and the three tandem pressure chambers. This increase in available operating force permits operation under lower heads at the close of the irrigation season when When the valves have the reservoir levels are drawn down. been idle for a long time, the friction of the needles may be increased by corrosion or scale depositions and additional force may be required to operate them. The needles are prevented from "slamming" when they reach the limits of their travel in either an opening or closing direction, by arranging the port apertures so that the speed is gradually reduced. Control and air-vent stands for the valves may be mounted either upon a floor above or directly on the upper side of the valve body. Two 60-inch valves of this type were installed at Gibson Dam, another pair of the same size at Echo Dam, and still another pair at Coolidge Dam. As a result of the experience derived from the operation of these and subsequent installations, additional improvements and revisions have been made in design. Some difficulty was experienced in preventing too much leakage from passing between the bore of the needle body and the exterior diameter of the diaphragm, from chamber B into chamber C, and thence into A. This was corrected by putting a heavy snap piston ring around the outer diameter of the diaphragm. When the valves were wide open, the high velocity of flow passing over the conical face of the needle was found to be producing a very pronounced suction or aspirator effect upon chamber A, by drawing water out of the cham h ber and its interconnected chamber C, through the clearance between the exterior cylindrical surface of the needle and the bore of the bronze liner in the front end of the cylinder. This made it hard to get the needle started moving toward the closed position under certain conditions of operation. It was also discovered that when the valves were closed, the conduit pressure in the water passageway surrounding the needle forced water inward through the same clearance into chamber A and from there into C, causing a force tending to hold the needle against its seat. This condition was only partially relieved, under certain operating conditions, when the control spear was withdrawn from the tube in the end of the needle. No practicable means were found for preventing the outward or inward flow of water through this clearance. This condition was finally corrected by changing chamber A into a plain cavity with a liberal drain to carry the inflow away before it could build up any appreciable pressure, as shown in figure 5, and by discontinuing the interconnecting passage between chambers A and C. By this arrangement chamber B was used as before to open the valve, and chamber C was used only to close the valve. Chamber B is exhausted to the atmosphere during the closing cycle by means of a new control known as the paradox control, see figure 6, located beneath the valve. and placed in communication with chambers B and C by means of cored passageways formed in the bottom radial rib. This control utilizes two moving elements, consisting of a cylindrical male member with a coarse, rapid pitch multiple thread upon its external diameter, meshing with the female member having a similar thread tapped into the hub of a three-spool valve mounted to travel vertically in the multiported control body bolted to the bottom of the needle valve. Valves equipped with paradox control have a number of advantages over their predecessors. The control system makes it possible to hydraulically move the needles throughout the extreme ranges of travel without requiring the presence of water in the conduits. This feature has proved to be most advantageous, as it makes the routine inspection and scale removal operations much easier to perform. Twelve 84-inch valves of this type are installed in the canyon-wall outlets at Boulder Dam and twelve 72-inch valves of similar construction are installed in the tunnel-plug outlets. Valves of this type have proved to be economical to build and capable of giving satisfactory and dependable service. The marked reduction in the physical dimensions of the valves makes possible substantial reductions in the size of the control structures and a corresponding reduction in cost. Two 84-inch valves of this type were installed at Madden Dam. These valves were tested by piezometers in the supply conduits to determine flow and discharge capacities. Results of the tests, which have not been completed, indicate that the coefficient of discharge will exceed 75 percent, based on the total net effective head at the inlet flanges and the gross nozzle areas. Pressure-rise tests were likewise made by closing the valves as rapidly as possible. It was found that the maximum pressure rise attainable was less than 2 pounds per square inch. Preliminary tests conducted on the 84-inch internal differential needle valves at Boulder Dam indicated coefficients ranging from 75% to more than 80 percent. Further tests on the same valves indicated a coefficient of discharge of 78 percent. The valves were tested by a calibrated Pitot tube and piezometers at the outlet conduits. Figure 8 shows capacity curves for balanced needle valves, based on tests of the Tieton valves. The curves are conservative for valves of later design. The marked scale depositing characteristics of waters encountered in some western watersheds made evident the desirability of providing a superabundance of operating force in needle valve control mechanism. This made it particularly desirable to find some practicable means whereby inward or outward leakage through the clearance space between the exterior of the needle body and the bore of the needle cylinder, prevalent in the first internal differential needle valves, would be prevented, thereby making available the closing force which could be produced in chamber A, without the attendant disadvantages manifest in those valves. Much study was devoted to the problem, with only discouraging results, until finally a workable solution was found in a quite marked modification of the internal differential needle valves. This led to the development of a type of valve known as an "interior differential needle valve." INTERIOR DIFFERENTIAL NEEDLE VALVES In this valve the needle cylinder, formed in the body and nozzle of its predecessor, has been eliminated, and the equivalent has been provided by forming the cylinder inside of the needle, as shown in figure 9. By this arrangement, the needle, instead of telescoping inside the cylinder as previously occurred, now telescopes over a member fixed to the valve body known as the body extension. The exterior diameter of the needle body forms the inner boundary of the annular water passage through the valve. This permits the use of a smaller diameter than before, and in consequence reduces the over-all diameter and length of the valve. The change resulted in a saving of about 25 percent in valve weight. By this arrangement of needle mounting, the entrance of the circumferential operating clearance space, between the bore of the needle and the cooperating diameter of the supporting body extension, is now placed at the upstream end, instead of at the downstream end where the higher velocity of flow tended to produce a strong suction when the previous valve was discharging. This rearrangement also made possible the installation of an expanding piston ring, found so effective in preventing leakage between chambers B and C in the previous valves, in the valve body extension to prevent leakage through that clearance space in either direction, thus making practicable the employment of cavity A as a pressure chamber under all conditions of operation. The changed construction and rearrangement of the parts results in chamber A being a complete chamber instead of an annular chamber; chamber B remains unchanged as an annular chamber; and chamber C is changed from a complete chamber to an annular chamber, due to the diaphragm tube being fastened to the needle. In this valve, the problems of drainage and air venting of the chambers are made simple and more efficient, as the presence of the valve body extension makes possible the installation of a direct drainage port from chambers C to A, at a location low enough to remove practically all water by gravity flow. A similar port on the upper side allows all the air in A to escape. Chamber B is likewise served by a port in its lowest portion, insuring complete drainage, and by a complimentary port in its high side, for venting. This makes possible the elimination of the intercommunicating bleeder ports between chambers C and B and from B into A, formerly required, as the ports from chambers A and C and from chamber B to the paradox control now serve as gravity drains as well. The paradox controls used with these valves are essentially the same as those used with the internal differential valves, except that they do not include the separate cylindrical screw actuated drain valve. This member is not required since the former cavity A is now made into a pressure chamber and no longer requires a separate drain outlet through the control. Interior differential needle valves have been, or are being, installed in the outlet works of the following dams: Two 36-inch valves at Moon Lake Dam, two 36-inch valves at Agency Valley Dam, two 42-inch valves at Boca Dam, two 48-inch valves at Taylor Park Dam, two 54-inch valves at Alamogordo Dam, two 60-inch valves at Seminoe Dam, and two 66-inch valves at Bartlett Dam. NEEDLE-VALVE OUTLETS Needle-valve outlets may be divided into four general classes, as follows: 1. On the water face of the dam, as at Arrowrock and Belle Fourche Dams, and in the South Tunnel Outlet at Pathfinder Dam. Installations of this character were discontinued after the balanced needle valve was developed for installation at the outlet ends of closed conduits. 2. On the downstream face of the dam, as at Owyhee and Gibson Dams. 2a. At the outlet ends of the diversion tunnels, as at Tieton and McKay Dams. 3. Inside of diversion tunnels as at Alcova and Boulder Dams. 4. At the outlet ends of tunnels or galleries provided for the sole purpose of releasing water from a reservoir under lesser head than that prevalent at the diversion tunnel level, as the Canyon Wall Outlets at Boulder Dam. These four main divisions are susceptible of further subdivision in accordance with the arrangement, type, and location of the service or emergency gates guarding the valves. For example, under class 2, the 4- by 4-foot highpressure gates that guard the 48-inch needle valves at Owyhee Dam, figure 10, are in a separate gallery near the upstream face of the dam, while the 5- by 5-foot highpressure emergency gates guarding the 60-inch needle valves at Gibson Dam, figure 11, have the outlet flanges of the gate frame transitions bolted directly to the inlet flanges of the needle valves. |