1.18 Standard Sizes (Cont.) HYDRAULIC GATES (Continued) HIGH-PRESSURE CONTROL AND EMERGENCY GATES (Continued) FOLLOWER GATES RING- .18 Ring-follower gates, used primarily for emergencies, are usually placed upstream from a regulating valve or service gate, and are operated either in a fully opened or fully closed position. A ring-follower gate is a slide type with an extended leaf through which a circular hole equal in diameter to that of the conduit forms an unobstructed water passage when the leaf is in the open position. The operating mechanism is usually a hydraulic cylinder and piston connected to the leaf by a stem passing through a packing in the valve body. An assembly drawing of the 102-inch ring-follower gate is shown in Figure 25. Design Considerations Materials & Stresses A. The design head on the leaf will be the static head plus water hammer that may occur on the area enclosed by the outside of the seat ring. The force required to start the gate opening will be this static head multiplied by the coefficient of starting friction between the leaf seal and body seat, usually taken as 0.6. The operating pressure in the hydraulic cylinder should be limited to about 750 psi and the cylinder should be designed for 1,000 psi. B. The gate body is usually made of cast iron and is not designed to support the hydraulic load, which is carried by reinforcing in the surrounding concrete. Working stresses are governed by the same considerations discussed in Subparagraph 1.6B(5). The effect of size on the tensile strength of gray iron in shown in Figure 26. RING-SEAL .19 Ring-seal gates are commonly used as either service or emergency gates in GATES penstocks located upstream from the turbines or in other conduits located upstream from regulating valves. They are used singly or in pairs; not, however, as regulating valves but in a fully opened or fully closed position. A ring-seal gate consists of a roller- or wheel-mounted leaf, moved vertically by an electric motor through a gear-reduction unit and a pair of threaded stems, 1.19A HYDRAULIC GATES (Continued) HIGH-PRESSURE CONTROL AND EMERGENCY GATES (Continued) A. The upper portion of the gate leaf forms a bulkhead section to stop the flow of water; the lower portion forms a circular opening of the same size as the conduit to produce an unobstructed water passage with the leaf in the open position as in the ring-follower gate. B. Complete closure of the leaf in the lower position is made by extending a movable ring seal, actuated hydraulically from the water pressure in the conduit, to contact a seat on the leaf. This ring seal is usually located in an annular recess in the gate housing and is placed concentric with and around the conduit opening into the gate body. However, some ring-seal gates are designed with the ring seal in the gate leaf instead of in the housing. C. The housing is usually made of cast iron and is not designed to support the hydraulic loads, which are carried by reinforcing in the surrounding concrete. D. The design head on the leaf will be the static head plus water hammer that may occur on the area enclosed by the center line of the seat ring. The force required to raise the gate will be the sum of the following: Axle or roller friction Guide friction The Gate Ring Seal Cast-Iron Design Considerations Weight of lifted parts. E. The working stresses are governed by the same considerations discussed in Subparagraph 1.6B(5). The stress in steel parts, such as the threaded forged stem, seamless tubing, etc., should not exceed 75 percent of the yield point of the material when the breakdown load of the motor is taken in one stem. F. Typical ring-seal gate designs are illustrated in the following drawings: Working Stresses Reference .20 Jet-flow gates are designed for use as regulating gates either at the discharge end of, or at any intermediate point in, a conduit. The gate consists of a leaf moved vertically on wheels, by means of a motor, gear reduction unit, and a pair of threaded stems, with the leaf and surrounding housing shaped so that the water will issue from the orifice in a jet at all leaf positions. Details of this gate are shown on Figures 28 and 29. A. The size and shape of the conduit are important elements in producing the B. To permit close and constant regulation the drive unit is usually a mechanical type instead of a hydraulic cylinder. The leaf is mounted on wheels to reduce friction. The design head on the leaf will be the static JET-FLOW Hydraulic Design Considerations Mechanical Design Considerations 1.20C Seal Housing Working HYDRAULIC GATES (Continued) HIGH-PRESSURE CONTROL AND EMERGENCY GATES (Continued) head plus water hammer that may occur on the area within the seal ring. The force required to raise the leaf will be the sum of the following: Weight of lifted parts Seal friction. C. Complete closure with the leaf in the lowered position is made by means of a constant contact seal against the upstream face of the leaf. The seal consists of a bronze wearing-ring vulcanized to a rubber diaphragm which is clamped to the downstream surface of the nozzle and is held in contact by the hydrostatic pressure of the water behind the seal. D. The flow characteristics are such that the gate body and cover are subjected E. The working stresses are governed by the considerations of Subparagraph 1.6B(5). RADIAL HINGED-TYPE GATES .21 Radial gates are so named because they are made to the shape of a portion of Gate Members A. A standard radial-gate installation consists of the following: Design Symbols Leaf, including faceplate, horizontal beams, and vertical side beams B. The following symbols are used in designing standard radial gates: C. In designating the size of a radial gate, the width, A, is given first, followed by the height, H. The height of a gate is the vertical projection of the distance from the sill to the top of the gate, and the head on all standard gates is assumed to be the same as the height. D. Standard radial gates are designed to cover a 2-foot width differential and a 1-foot height differential. The radius of the inside of the faceplate is 1.250 times the minimum height, R = 1.25(H-1.0). The height of the pin is placed between one-half of the minimum head, H-1.0, and three-fourths of the maximum head, H. The pin height used for any specific gate installation is designated as Y on standard drawings of gate and wall plates and is given in the specifications. E. The maximum length of arc is obtained for gate height H, and the pin F. The approximate water load on the gate is calculated from the formula G. The following shows the design stresses ordinarily used in designing Design Symbols (Cont.) Proportions of Gates Design Considerations Determination of Arc Length Hydraulic Design Stresses Minimum thickness of metal in plate and rolled section equals one-fourth inch, except that web thickness of horizontal beams may be less for more economical section. 1.21H Design of Design of Transverse Beams Design of Side Beams Design of Design of Hub & Pin Bearing Design of Pin-Bearing Brackets HYDRAULIC GATES (Continued) HINGED-TYPE-GATES (Continued) A standard gate is designed for the maximum head, H, and the maximum width, with the maximum pin height, 0.75 H. These conditions give the maximum load on the gate. H. The effective thickness of the faceplate is taken as one-sixteenth inch less than the nominal to allow for corrosion. The faceplate is considered to be composed of beam strips, 1 inch wide and of length 1, equal to the distance between the flanges of the horizontal supports. The continuity of the beam strips over the supports is partially considered in the use of the formula for the moment, M W1, where W is the total load on the strip. A = 10' thickness of plate is chosen to give a reasonable spacing of the horizontal beams, usually not less than 12 inches. The beam spacing increases progressively towards the top as the water pressure decreases. = I. The horizontal beams are designed as continuous over two supports with J. The side beams are built up from plate and welded, one side of the beam K. Each gate arm is composed of two members fastened to the side beams of L. Each hub is bushed with a bridge-bearing bronze bushing self-lubricated M. Pin-bearing brackets are designed for a maximum bearing stress between pin and bracket lugs of 10,000 psi, and a maximum allowable bearing on concrete grout of 500 psi. Pin bearings are set so that the base is normal to the resultant force W. This eliminates the load on the anchor bolts when the gate is seated. The anchor bolts are designed for shear and tension and for bending and bearing on the concrete when the gate is in the raised position. |