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upon which the vertically moving leaf and ring follower are supported and seated.
The leaf castings are usually made of cast iron of about 50,000 pounds per square inch strength for the lesser heads, of steel castings for higher heads, and of alloy cast steel having a minimum ultimate strength of 80,000 pounds per square inch and a yield point of not less than 50,000 pounds per square inch, for still higher heads.
The method of attaching the gate stem to the leaf, the general construction of the upper bonnet cover, the hoist cylinder, and the piston is similar to the latest type of highpressure gate construction previously described. The upper cylinder head, however, is modified to receive a cylinder head gate hanger which is enclosed and contains a pair of swinging jaws operating in a horizontal plane that engage the under face of the stem extension cap. This cap is retained by a safety stud which is necked to break without injury to other parts of the equipment, should malfunctioning of the hanger occur. A small oil-operated cylinder wedges the jaws apart to release the hanger whenever oil pressure is introduced into the lines to operate the hoist.
PARADOX GATES As a companion to the ring-follower emergency gates, there has been developed by the engineers of the Bureau, a service gate for opening or closing off the flow through conduits of sizes up to 102 inches in diameter, under heads up to and in excess of 600 feet. Gates of this type, when used in conduits, are known as paradox gates.
Paradox gates have a number of features similar to ringfollower gates, inasmuch as they provide circular waterways with practically unbroken wall surfaces by similar ring-follower members beneath their leaves, as shown in figure 4. They likewise have bonnets extending beneath their conduits to receive the ring-follower members when the leaves are lowered for closure. They are also provided with air inlets in the upper portions of their waterways, immediately downstream from the gate leaf faces in substantially the same manner as in ring-follower gates.
Paradox gates descend or ascend in closing or opening while supported by vertical endless trains or belts of rollers that extend along either side throughout practically the entire height of the gate leaf and its follower ring. The leaf is lowered in closing until the bronze seal ring affixed to the downstream face of its bulkhead portion is brought into horizontal alignment with the mating bronze seat ring enclosing the water passageway in the adjacent face of the downstream gate frame, whereupon further downward movement of the leaf is arrested by lugs on the under side of the follower ring coming into contact with stops arranged for that purpose in the bottom bonnet cover. Meanwhile the roller carriage continues its descent some 11 inches farther, withdrawing the inclined roller trains and permitting the gate leaf to move horizontally about one-eighth
FIGURE 2.-Single air vent pipe sizes for ring follower and
above. The lower end of the lower bonnet is closed by a cover bolted to its lower flange face. In this lower cover, one or more drain outlets of ample area are provided to permit draining the interior of the entire gate, and to flush out any sediment which may collect in the bottom of the bonnet.
An air inlet manifold is cast integral with the downstream gate frame, around the upper exterior surface of the water passage wall; and a series of 17h-inch diameter cored holes, equally spaced in staggered relationship in four circumferential rows, admit air to the conduit in close proximity to the downstream face of the gate leaf. Two symmetrically positioned inlet flanges admit air to this distributing manifold from an air inlet pipe carried to a screened inlet located at an elevation above high water level in the reservoir.
The gate leaf is usually made in two parts, bolted together, consisting of the upper bulkhead section and the lower ringfollower unit. On the downstream face of the leaf are facing rings and vertical runner strips of class D bronze. Similar rings and strips of class C bronze are fastened with flat head bronze screws to the upstream faces of the downstream gate frames and bonnets, to form the sliding ways
for drilling template of
upstream ond down.
FIGURE 3.-Ring follower emergency gate.
inch downstream until its seal ring contacts the seat ring. This completes closure and allows the water load on the leaf to be transferred through its seal ring into the supporting seat ring of the gate frame.
In opening the gate, the roller carriages first start moving upward until they engage the inclined roller trains with the downstream inclined surfaces of the leaf. Continued upward movement of the carriages then forces the roller trains to wedge the leaf away from contact with its seat, causing a horizontal separating movement of about oneeighth inch. When this has been accomplished, the toggles connecting the leaf and the cross-head are extended; whereupon the gate leaf with its ring follower, the two inclined roller trains, and the two roller carriages all move upward in unison until the ring follower is brought into axial alignment with the water passage.
The foregoing description shows that no sliding contact between seating and sealing surfaces occurs while the gates are passing through their opening or closing cycles. Consequently, the surfaces are not subjected to the rapid wear and deterioration that results when sliding contact occurs under high intensity loadings. Inasmuch as all movements of the gate leaf occur while it is supported on roller train systems, the force or power input required for operation is relatively small.
Paradox gates are not suitable for operation at partial openings. They are used as service gates at Grand Coulee Dam because the quantities of water handled are so large that ample regulation of reservoir release can be obtained by opening or closing one or more of the battery of twenty 102-inch gates in the lower tier, or similar gates in the two upper tiers.
ENSIGN VALVES When the rectangular gates at Roosevelt Dam demonstrated the impracticability of reservoir outlet regulation with that type of equipment in 1908, O. H. Ensign, then chief electrical engineer of the Bureau, seeking a means to overcome the trouble, invented the Ensign valve. Ensign valves were installed at Roosevelt, Arrowrock, and Belle Fourche Dams, and in the South Tunnel Outlet of Pathfinder Dam. They were placed on the water faces to control discharges through conduits piercing the dams. They proved successful where the reservoirs are drawn down at frequent intervals, so that the valves are exposed for servicing and maintenance work. At large hold-over reservoirs, where the outlets may be submerged for several years, the valves may become inoperative due to corrosion or scale encrusting and may require the draining of the reservoirs to a level where repairs can be made.
This valve is generally known as a balanced valve of the Ensign type. It consists of a central, horizontally mounted, cylindrical piston, with the downstream end curved and pointed to guide the discharge into the conduit, the opposite end being enlarged to form the bull ring
The bull ring is closely fitted into a bronze-lined cylinder which is bolted to a heavy radially ribbed cage anchored to the face of the dam. A circular flange is provided, surrounding the discharge passage and concentric therewith. The inner edge of this flange forms the seat against which the forward end of the needle rests when the valve is closed.
A slight clearance is provided around the circumference of the bull ring to permit passage of water to equalize the pressures on both sides of the piston when the control pipe is closed. When the pressures are thus equalized the valve is closed and the piston or needle is held against its seat, the pointed end in the water passage being subjected to atmospheric pressure and the back of the piston and bull ring being under full reservoir pressure. By opening the control valve, whose discharge area is larger than the clearance area around the bull ring, the pressure on the upstream side of the bull ring and piston is reduced, whereupon the reservoir pressure, acting against the annular downstream face of the bull ring, causes the needle to move upstream, thus opening the valve. Conversely, by closing the control valve, the pressure on the upstream side of the bull ring and piston is increased; and, as this area is much greater than the annular area on the downstream face of the bull ring, the excess force causes the needle to move toward its closed position.
Discharge conduits from balanced valves have been made of cast iron, plate steel, or, in some instances, have been formed in concrete and lined with a carefully placed and smoothed rich cement mortar. Cavitation, resulting from a vacuum immediately beyond the inlet entrance to the conduits, has seriously damaged cast iron and steel linings. The conduits in the South Tunnel Outlet at Pathfinder Dam were repaired by installing bronze bellmouth inlet castings, then lining the balance of the conduits with rich concrete. A number of 1;2-inch pipes, connected with the bronze bellmouths, were embedded to supply air to the annular space around the exterior of the bellmouths, and from which air gained entrance to the conduits through a series of 1-inch holes in the bellmouth walls. The new linings have been in use 14 years and show but little signs of deterioration.
Experience with Ensign balanced valves showed that such equipment should be placed where it is readily accessible at all times. This led to the development of what are known as balanced needle valves.
BALANCED NEEDLE VALVES Balanced needle valves, as first developed by the Bureau, were placed in the downstream ends of the conduits instead of the upstream ends. The hydraulic conditions of operation and control were practically the same as for the Ensign valves. One great advantage which the new type possessed, besides that of accessibility, was that the enormous energy stored in the water passing through the valve was released
into the open instead of being largely expended in the destruction of the conduit.
The two 58-inch balanced needle valves in the North Tunnel Outlet at Pathfinder Dam, were the first valves of this type installed by the Bureau. These valves have been in successful operation since 1921, the only trouble experienced being some damage to the inner control mechanism. This damage was caused by failure of the operator to vent the air from the interior of the valve as it was being filled with water by opening the emergency gate behind it.
Profiting from experience derived at Pathfinder Dam, the 60-inch balanced needle valves for Tieton and Lahontan Dams were designed with the control apparatus placed outside the valves, in cases bolted to flanges provided on the upper sides of the valve bodies. This type of control has proved satisfactory. Operation of the Tieton valves revealed that the cylinder walls of the control had not been made as heavy as required and consequently went "out of round” where the ports pierced the walls. This condition was relieved by admitting conduit pressure to the closed side of the outer sleeve by means of a 3-inch pipe, and by providing high-pressure lubrication with a heavy oil.
In designing the Tieton valves, the water passages were proportioned so that the velocity is constant until the water reaches the forward portion of the valve and starts to converge inward to pass along the conically pointed needle and out through the nozzle. When this point of travel is reached, the passages are shaped and proportioned so that the velocity is gradually accelerated on a sine curve until maximum velocity is reached as the water issues from the nozzle. This change was based on a series of tests conducted on a 4-inch experimental model. It resulted in a considerable improvement in performance and efficiency over that obtained with the Pathfinder valves. The two 60inch balanced needle valves at Tieton Dam were tested by the salt brine injection method and the coefficient of discharge, based on the total effective head at the entrance flanges and the gross nozzle areas, was found to be 7272 percent as compared with 62 percent for the Pathfinder valves.
When the cylinder controls were being designed for the 48-inch balanced needle valves for McKay Dam, advantage was taken of the experience obtained at Tieton Dam. The control cylinders were made heavier, and when later put into operation proved very satisfactory.
INTERNAL DIFFERENTIAL NEEDLE VALVES
lengths. These values are known as “internal differential needle valves.”
In valves of this design, the interior is divided into three tandem pressure chambers, designated A, B, and C. These chambers are formed by a fixed diaphragm, inside the needle, supported by a heavy diaphragm tube concentric with the axis of the valve, with the rear end terminating in a flange bolted to the valve body. The rear end of the needle is closed by a hemispherical head. The head is provided with a bushed hub which rides on the diaphragm tube as the needle and its attached head move back and forth in opening or closing the valve. The exterior cylindrical surface of the needle is telescopically mounted in an enclosing cylinder, supported by radial ribs extending through the water passage from the walls of the exterior shell.
Chambers A and C are interconnected by passages formed in the diaphragm tube; so that water can readily pass from one to the other in either direction. Consequently, the pressures in these two chambers are always equalized. Pressure introduced into the chambers causes the needle to move in the closing direction. When the pressure is released in chambers A and C, the pressure in chamber B produces a force on the inner face of the hemispherical needle head which causes the needle to move in the opening direction. Chamber B is connected to the conduit at all times and consequently has reservoir pressure therein.
The sliding clearance between the bore of the bushing in the hemispherical needle head and the cylindrical surface of the diaphragm tube, permits a slow transfer of water from chamber B to chamber A, then into chamber C through the interconnecting passageways in the diaphragm tube. From this it will be seen that if water is prevented from escaping from chambers A and C, the infiltration from chamber B will soon establish substantially equal pressure in all three chambers. When this occurs, the preponderance of closing forces so engendered in chambers A and C are greatly in excess of the opening force produced in chamber B, and the needle will start moving toward the closed position. This will diminish the cubical contents of chamber B, causing part of the water to be forced back into the conduit.
Water from chambers A and C is released through the needle tip by a manually controlled spear operating in conjunction with a tube carried in the tip of the needle. The forces acting upon the needle and piston of this valve are different from those on the valve previously described and are as follows:
Opening forces.—(a) Conduit pressure within chamber B acting against the concave face of the movable needle head.
(b) Conduit pressure acting against that part of the downstream conical end face of the needle that is of greater diameter than that of its line contact with the valve seat when the needle is in the closed position.
(b-1) Jet reaction and pressure upon the downstream
In 1928, a new principle of operation was developed, which resulted in materially reducing the physical dimensions, weight, and cost of needle valves. The new valves are arranged and constructed so that the annular external ring around the needle or piston, commonly known as the “bull ring,” is eliminated, making possible a marked reduction in the external diameters of the valves, accompanied by an even more marked reduction in the over-all