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HYDRAULIC GATES (Continued)
Semiautomatic gate hangers:
Hydraulic gate hangers:
High-pressure Gate Assembly with Hydraulic
High-pressure Gate Control--Oil Piping
RING- .18 Ring-follower gates, used primarily for emergencies, are usually placed FOLLO WER upstream from a regulating valve or service gate, and are operated either in
GATES 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 A. The design head on the leaf will be the static head plus water hammer Considerations 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 so be limited to about 750 psi and the cylinder should be designed for y DSl.
Materials & B. The gate body is usually made of cast iron and is not designed to support Working the hydraulic load, which is carried by reinforcing in the surrounding Stresses 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, or by means of a hydraulic cylinder. An assembly drawing of the 86-inch ring-seal gate is shown in Figure 27.
HYDRAULIC GATES (Continued)
A. The upper portion of the gate leaf forms a bulkhead section to stop the
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 Considerations
force required to raise the gate will be the sum of the following:
Axle or roller friction
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:
102-inch Ring Seal Gate--Green
126-inch Ring Seal Gate--Boysen
.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 desired jet characteristics. From a point approximately one diameter
upstream from the face of the gate leaf the conduit is flared outward at a Considerations
slope of 1 in 12 to a diameter of 120 percent of the jet orifice. From this
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
Mechanical Design Onsiderations
HYDRAULIC 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
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 * stresses are governed by the considerations of Subparagraph 1.6B(5).
Radial gates are so named because they are made to the shape of a portion of
A. A standard radial-gate installation consists of the following:
Leaf, including faceplate, horizontal beams, and vertical side beams
Four or six guide rollers
Hoist with anchor bolts.
B. The following symbols are used in designing standard radial gates:
A = width of gate
1.21C HYDRAULIC GATES (Continued) HINGED-TYPE GATES (Continued)
pin height selected for specific installation Design Symbols
. In designating the Size of a radial gate, the width, A, is given first, Proportions
followed by the height, H. The height of a gate is the vertical projection of Gates 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.
Standard radial gates are designed to cover a 2-foot width differential and Design a 1-foot height differential. The radius of the inside of the faceplate is Considerations 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.
. . The maximum length of arc is obtained for gate height H, and the pin Determination
bearing set at maximum height, 0.75 H. The minimum length of arc is of Arc Length obtained for gate height H-1.0, with pin bearing set at minimum height, 0.50(H-1.0). The difference between the maximum and minimum length of arc equals the maximum value of E. This maximum value of E is given on the standard drawing of the gate. For any height of gate between H and H-1.0 and any value Y between maximum and minimum, the dimension E has to be calculated and is given on standard gate drawings and in
The approximate water load on the gate is calculated from the formula Hydraulic
W = 34 AH2. The resultant of the horizontal and vertical components of Forces
the water load is assumed to act at a point located one-third of the head
above the gate sill and on a line through the pin bearings. The exact method
for determining the water load requires that the horizontal and vertical
components be calculated. From these, the resultant or total water load can be determined. The direction of the resultant can best be found by layout and will lie through the axis of the pin bearings. The following shows the design stresses ordinarily used in designing Design radial gates: - Stresses
Hot-rolled sections--structural Steel 18,000 3-1/3
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.
A standard gate is designed for the maximum head, H, and the maximum
Design of H. The effective thickness of the faceplate is taken as one-sixteenth inch less
Gate Leaf 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 = W!, where W is the total load on the strip. A
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. Design of I. The horizontal beams are designed as continuous over two supports with t Transverse uniformly distributed load. The formula for the bending moment is
Beams M = %1(1-4K) in which w is the total water load over the section of
faceplie supported by the beam, l is equal to the width of the gate, Kl is the distance from the center line of the side beam to the side of the gate. The faceplate is not considered in determining the size of beam to be used.
Design of J. The side beams are built up from plate and welded, one side of the beam
Side Beams being curved to fit the faceplate. For the purpose of design, the side beams are considered to be straight and of a length equal to the arc of the faceplate. The load on each beam equals one-half the water load on the gate, increasing uniformly, from top to bottom, as the head increases. Each side beam is supported at two points by the gate arm. The distance to the points of support is measured along the inside of the faceplate. In terms of the length of arc the distance from the sill to the center line of the bottom arm member is 0.123 L. The distance between center lines of arm members is 0.4912 L. This spacing of the arm supports of the side beam is based on an analysis of the moments in the beam (an overhanging beam with two supports), such that the moment between the supports is equal to the moment over either support but of opposite sign.
Design of K. Each gate arm is composed of two members fastened to the side beams of Arms the gate leaf with rivet bolts. Each member is designed as a column with an 1% ratio equal to or less than 120, where r is the least radius of ation. The lower arm carries a load of 0.31 W, and the upper arm .21 W, where W is the water load on the gate. The two members converge and are connected to a hub.
Design of L. Each hub is bushed with a bridge-bearing bronze bushing self-lubricated Hub & Pin with graphited inserts, the area of the inserts being equal to 20 percent of Bearing the bearing area. The maximum allowable bearing pressure equals 3,500 psi. The load on each pin equals W/2. The pin is designed for bearing or bending, whichever requires the larger size. Maximum allowable bending stress in the pin equals 23,000 psi. Pins are made of SAE 1045 steel, hot-rolled. Shearing stresses in the pin are very small.
Design of M. Pin-bearing brackets are designed for a maximum bearing stress between Pin-Bearing pin and bracket o of 10,000 psi, and a maximum allowable bearing on Brackets 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.