In outlet works of the type constructed at Gibson Dam, where the gates are located at the toe of the dam, with the balanced valves directly connected to the emergency gate, the downstream frame of the gate is formed as a transition with stream lines carefully designed to avoid sudden changes in section and to provide a gradual change in the velocity of the water between the slide gate opening and the body of the valve. In this plan, it is necessary to design the downstream frame to withstand full reservoir pressure, and this is accomplished by the use of cast steel, with a system of ribs to provide ample strength.

Standard designs of high-pressure gates have been prepared covering a range of sizes from 21⁄2 by 21⁄2 feet to 5 by 6 feet clear gate opening. Provision for installation under varying heads is made by making the gate leaf of cast iron for heads up to 90 feet, of semisteei for heads up to 140 feet, and of cast steel for heads up to 250 feet. The same principle is used for the bonnet covers, which are designed to accommodate the proper size hoist cylinder for the head under which the gate will be operated.

REGULATING VALVES

The outlet report by Messrs. Gaylord and Savage describes the evolution of the balanced valve, from the first crude 2-inch experimental valve which operated successfully,' to the perfected Ensign type of valve installed on the upstream face of the dam, as at Roosevelt, Arrowrock, Pathfinder South Tunnel, and Belle Fourche dams, to the mechanically operated needle valves later installed at Roosevelt Dam, and to the original design of balanced needle valves installed in the North Tunnel outlet at Pathfinder Dam. As previously stated, there is little difficulty in regulating the discharge with slide gates under heads up to 75 feet, and large discharges can be regulated by this method at relatively small expense. For higher heads, however, it is advisable to use a different type of outlet, and for this purpose the needle type of valve was developed that would permit close regulation of the discharge without undue maintenance expense. The balanced valve of the Ensign type is adapted for high head discharges and can be used under any condition to which a needle type of valve is applicable. The design of such valves is simple and compact. They are installed on the water face of the dam, discharging into a conduit through the dam, and where the reservoir is frequently emptied and the valves thus made accessible, this plan has proven very successful. In case the reservoir has a large hold-over capacity, however, the valves may be submerged for a period of many years, and if they become inoperative it is necessary to drain the res

1 Invented by O. H. Ensign, chief electrical engineer, Bureau of Reclamation see High Pressure Reservoir Outlets, p. 6.

ervoir to make repairs. In such case a valve placed below the dam and connected to the reservoir by a conduit or pipe is much more desirable, and it was this condition that led to the development of the free discharge needle valves, as will be described in a succeeding section.

BALANCED VALVES

Balanced valves, of the Ensign type, were developed for installation above the dam, and discharge into a conduit passing through the dam. The general design is shown in the accompanying illustration. The balanced valve consists essentially of a cylindrical piston with one end pointed to guide the discharge, the other end being provided with an enlarged end, termed the "bull ring," to give a differential in pressure, and closely fitting into a closed stationary cylinder in which it moves. The valve seat is circular and is placed in the base of the valve.

A sufficient clearance around the bull ring is provided to permit passage of water to equalize the pressure on both sides of the piston when the control pipe is closed. With pressures equalized, the valve piston will be held against the seat like a check valve, since the pointed end is subjected to atmospheric pressure only, while the back of the piston is under full reservoir pressure. By opening the control valve which is larger in discharge area than the clearance around the bull ring, the pressure on the back of the piston is reduced, and the pressure on the annular space in front of the bull ring will open the valve. Conversely, by closing the control valve, the pressure on the inside of the piston is increased till it exceeds that on the annular space, and the valve will close.

This

Of the twenty 58-inch balanced valves in Arrowrock Dam, six are provided with what is termed "positive control," by which the piston can be held at any intermediate position for regulation of the discharge. positive control consists of an acorn valve, attached to the head of the piston, which makes contact with a movable tube in the valve head, thus forming a control valve. The movable tube is controlled by a system of gears and shafts extending through the control pipe into an operating gallery inside the dam.

To hold the piston in the full open or the closed position by means of a simple valve in the control pipe line is an easy matter. For intermediate regulation of the discharge, however, the forces acting on the piston must be practically balanced. These forces are reservoir pressure acting on the annular ring, pressure and reaction of the jet on the needle end, both tending to open the valve, pressure inside the cylinder tending to close it, friction of the piston in its V guides and in the cylinder resisting motion in either direction.

With the "positive control," the control tube is withdrawn from the acorn valve to any desired position. The piston then moves open until the acorn valve approaches the control tube thus building up pressure back of the bull ring. The piston then moves more gradually until the water passing through the control is exactly the amount passing the bull ring when the pressures on both sides of the piston become balanced and it ceases to move.

Conduits for balanced valves have been made of cast iron, plate steel, and sometimes merely formed in the concrete and lined with rich cement mortar, carefully smoothed. The effects of cavitation, resulting from the formation of a vacuum immediately below the piston, have seriously damaged the cast iron and steel linings and they have proven unsatisfactory. At Pathfinder Dam, the conduits for the six valves in the South Tunnel were repaired by installing a bronze liner immediately below each valve, and lining the balance of the conduit, originally lined with cast iron, with rich concrete. The bronze liner was made with an annular space between it and the original conduit, with a number of 1-inch holes through to the inside. A number of 12-inch pipes were embedded in the concrete lining and connected to the annular space around the bronze liner, thus providing an air vent to the space where the vacuum had formed. These new linings have been in use for seven years and to date have shown no signs of deterioration.

BALANCED NEEDLE VALVES

The first balanced needle valves developed by the Bureau of Reclamation are in reality a "balanced valve" placed inside of a conduit. The hydraulic conditions of control and operation were identical, as were the factors used in their design. Their great advantage is that they are installed below the dam, with the enormous stored energy in the water released into the open.

The first balanced needle valves put into sevice were two 58-inch valves in the North Tunnel at Pathfinder Dam. These valves were provided with the acorn and sleeve control on the axis of the valve, actuated by gears and shaft extending to a control table on the floor above the valves. With this control it is possible to regulate the discharge for any quantity from 0 to 1,200 second-feet. These valves have been in successful operation since 1921, the only trouble experienced having been damage to the control mechanism on the inside of the valve. This damage was caused by failure of the operator to vent the air from the inside of the valve when it was filled by opening the emergency gate. The needle or plunger stuck in the cylinder from having been inoperative for some time, and when the pressure had reached a point sufficient to overcome the resistance, the plunger moved suddenly and traveled a suf

ficient distance to jam the acorn valve into the control sleeve, and bend the control stem so that it could not be used. The design of this control apparatus has now been modified by using a plain plug moving inside a tube, so that if the operator should fail to vent the valve, and the plunger opened suddenly, the control members would merely telescope without damage. Similar troubles have been experienced with the Ensign type of balanced valves at Arrowrock Dam. This has

not been a serious matter as the Arrowrock valves are unwatered every year by the draft of irrigation water from the reservoir; thus they are readily accessible for repairs.

The 60-inch balanced valves at Tieton Dam were designed on the same general hydraulic principle as the Pathfinder valves, but because of operating troubles experienced with the latter valves, the control apparatus was placed outside the body of the valve. This control, termed "cylinder control" is by means of two cylindrical sleeves, one moving inside the other, with suitable ports for release of water used for balancing purposes, both sleeves being mounted in a cast iron control case. One sleeve is actuated by the valve plunger, through a rack and pinion, gears and shaft, the other cylinder by a handwheel outside the valve. By rotating the outer cylinder by means of the handwheel, ports in the sleeves are uncovered, releasing water to the atmosphere and reducing the internal pressure in back of the plunger, allowing the valve to open. Conversely, by closing the ports in the control sleeves, the internal pressure back of the plunger is increased, causing it to close. An indicator is provided to show the position of the needle at any point in its travel. In the design of these valves the body was so designed that pipe-line velocity is maintained until the water reaches the nozzle, and there the change from pipe-line velocity to full spouting velocity is gradual. This change in body design was made after tests of a 4-inch experimental valve, and resulted in a considerable increase in efficiency.

The cylinder valve type of control has proven very satisfactory but in the Tieton valves the control sleeves were not made heavy enough, and they have a tendency to distort owing to unbalanced pressures at certain points of rotation. This condition was relieved by admitting pipe-line pressure to the closed side of the outer sleeve by a 1/2-inch pipe, and by lubricating them with a heavy oil.

The 48-inch balanced valves installed at McKay Dam have the same cylinder valve type of control, but the control sleeves are heavier than those in the Tieton valves, and operation has been very satisfactory. These valves have a discharge coefficient of 72.5 per cent based on the net head on the inlet to the valve and the gross area at the outlet, as compared with 62 per cent for the Pathfinder needle valves.

INTERNAL DIFFERENTIAL NEEDLE VALVES

During the past year (1928) a new principle for

operation of needle valves has been developed by

which the annular area around the piston is eliminated, thus materially reducing the weight of the valves and also the cost. The general design of the valve is shown in the accompanying illustration.

In this design the interior of the valve is divided into three sections of chambers, lettered A, B, and C on the drawing. These chambers are formed by a fixed diaphragm fastened on the end of a cylindrical tube, which, in turn, is bolted to a suitable flange on the body of the valve. The plunger telescopes into the cylinder, and on its inner end a piston or diaphragm is connected.

Operation by control of the hydraulic forces within the valve is by means of suitable passages and ports giving communication between the three chambers. Chambers A and C are connected by passages in such a manner that water can readily pass from one to the other as the plunger opens or closes in the normal operation of the valve and are exhausted to atmospheric pressure by passageways and control pipes that provide for control of the movements of the plunger. Chamber B is connected to the pipe line or conduit under reservoir pressure by a passageway permitting unrestricted flow in either direction. Chamber B supplies pressure very slowly to chamber A through restricted leakage past the movable piston on the plunger and the fixed diaphragm, which leakage is supplemented by a small port supplying conduit pressure to either chamber A or chamber C. With pressure conditions thus established within the valve, the plunger is subject to the following operating

forces:

Closing forces. (a) Conduit pressure within chamber A against the face of the movable piston with or without chamber B reduced to lower or atmospheric pressure. (b) Conduit pressure within chamber C against the conical end of the plunger, with or without chamber B reduced to lower or atmospheric pressure.

Opening forces.-(c) Conduit pressure within chamber B acting against the face of the fixed diaphragm, with chambers A and C reduced to lower or atmospheric pressure. (d) Conduit pressure against that part of the conical end of the plunger that is inside the contact with the valve seat in the nozzle, plus the reaction of the jet after the plunger has moved onward. This valve can be used in a pipe line, as in a penstock, in which the opening force available is conduit pressure against part or all of the conical end of the plunger.

With these different conditions of pressure available it is possible to force the plunger open or closed regulating the exhaust pressure out from chambers or to hold it in any intermediate position by suitably A and C and from chamber B. For example, when the pressure is entirely cut off from chamber B, and allowed to accumulate in chambers A and C, the plunger will be forced to close against its seat, whereas, if the pressure is permitted to accumulate in chamber B and is exhausted from chambers A and C, the plunger will be forced open. Likewise, when the closing pressures are equalized with the opening pressures by control of the exhaust from chambers A and C, at any position of the plunger, the load on each side of the plunger is balanced and it will remain fixed at partial opening until the hydraulic conditions within the valve are again changed. In the normal operation of the valve, chamber B is maintained under full conduit pressure at all times. and control is secured by regulation of the exhaust from chambers A and C. However, it is obvious that the pressure in chamber B can be decreased or increased as required, if necessary to secure proper actuating forces.

The differential between the opening and closing forces in this valve is greater than in any other known type of needle valve, owing to the large additional area of the movable piston on the plunger. This increased differential is of much value, as it insures greater forces to overcome friction in the plunger and for operation under low conduit pressures and constitutes one of the important features of this design. The friction of the movable plunger is often increased by corrosive action when valves are idle for a long period or where the water contains considerable quantities of chemicals that induce rapid coercion, and it is well known that commercial valves have failed to function properly for this reason.

The plunger is prevented from slamming in either direction by suitable restrictions in the communicating ports between chambers A and C, these ports being so shaped that when they engage at the finish of the stroke of the plunger their area is rapidly decreased, thus having a dampening effect. The passage of water berween chambers A and C, through the small ports, and from chamber B back into the pipe line gives a further dampening effect throughout full travel of the plunger.

The valves are designed for control and for venting by a control stand located on a floor above the valve, or by a handwheel mounted on the body of the valve, to suit any conditions of installation. Patents covering the internal differential feature of this type of valve are pending.