Gates and Valves for Flow Control (Part - 5) - Civil Engineering (CE) PDF Download

Design of important gates 

The important types of gates used for water resources projects are the following: 

1. Fixed wheel type vertical lift gates
2. Radial gates
3. Sliding gates 

The following paragraphs mention the salient features of these gates, the detailed design of which are available in the respective Bureau of Indian Standards codes as mentioned. 

Fixed wheel type vertical lift gates  

The fixed-wheel vertical lift gates comprise of, in general, a structural steel frame consisting of end vertical girders with properly spaced horizontal girders between them. The spacing depends on the design water pressure and on dimensions of the gate. The frame is held a piece by secure welding or riveting. Skin plate protects the structural framework from damage due to ice and heavy debris, minimizes downpull, reduces corrosion and facilitates maintenance. However, in some cases as in the case of fixed wheel gates moving on track provided on the face of the dam, skin plate is provided on the downstream side. In exceptional cases, skin plate is provided on both downstream side and upstream sides, if the down stream water is above sill. In such cases the gates maybe fully or partially buoyant. In case of fully buoyant gates, buoyancy shall be taken into account in determining the net balance of vertical forces and addition of ballast may be necessary to ensure lowering without difficulty. This problem is absent in the case of flooded gates but greater care against corrosion becomes necessary. The wheels are mounted on the end girders. The bottom of gate should be so shaped that satisfactory performance and freedom from harmful vibrations are attained under all conditions of operation apart from minimizing downpull. A typical arrangement of various components of gate is shown in Figure 24. Detailed design of this type of gates has been published by the Bureau of Indian Standards code IS: 4622-2003 “Recommendations for structural design of fixed wheel gates”. 

Figure 24. Vertical Lift Fixed Wheel Gate

Radial gates

Normally, the radial gate has an upstream skin plate bent to an arc with convex surface of the arc on the upstream” side (Figure 25 and 26). The centre of the arc is at the centre of the trunnion pins, about which the gate rotates. The skin plate is supported by suitably spaced stiffeners either horizontal or vertical or both. If horizontal stiffeners are used, these are supported by suitably spaced vertical diaphragms which are connected together by horizontal girders transferring the load to the two end vertical diaphragms. The end beams are supported by radial arms, emanating from the trunnion hubs located at the axis of the skin plate cylinder. If vertical stiffeners are used, these are supported by suitably spaced horizontal girders which are supported by radial arms. The arms transmit the water load to the trunnion/yoke girder. Suitable seals are provided along the curved ends of the gate and along the bottom. If used as a regulating gate in tunnels or conduits, a horizontal seal fixed to the civil structure, seals with the top horizontal edge of the gate, in the closed position. The upstream face of the gate rubs against the top seal as the gate is raised or lowered. Guide rollers are also provided to limit the sway of the gate during raising or lowering.

The trunnion anchorage comprises essentially of a trunnion yoke girder, held to the concrete of the spillway piers or the abutments by anchor rods or plate sections designed to resist the total water thrust on the gate. The trunnion or yoke girder is usually a built-up section to which the anchors are fixed. 

The thrust may be distributed in the concrete either as bond stresses along the length of the anchors (Figure 27) or as a bearing stress through the medium of an embedded anchor girder at the up stream end of the anchors. In the latter case the anchors are insulated from the surrounding concrete. 

Alternatively, anchorages of radial gates could also comprise pre-stressed anchorage arrangement. This system is especially advantageous in the case of large sized gates where very high loads are required to be transferred to the piers and the system of anchorages mentioned above is cumbersome and tedious. In this case pre-stressed anchorages post tensioned steel cables or rods are used which when subjected to water thrust will release pressure from concrete due to higher tensile stresses carried by anchorages.  

The Bureau of Indian Standards code IS: 4623-2003 “Recommendations for structural design of radial gates” may be referred to for further details on radial gates design. 

Figure 25. Downstream View of a Typical Tain Ter Gate

Figure 26. Primary Tainter Gate Components

Figure 27. Side View of a Radial Gate

Sliding gates 

Slide gates, as the name implies, are the gates in which the operating member (that is, gate leaf) slides on the sealing surfaces provided on the frame. In most cases, the sealing surfaces are also the load-bearing surface.  Slide gates may be with or without top seal depending whether these are used in a close conduit or as crest gate. A typical installation of a slide gate is shown in Figure 14. These consist of a gate leaf and embedded parts. These embedded parts serve the following purposes:

a) Transmit water load on the gate leaf to the supporting concrete (structure),

b) Guide the gate leaf during operation, and  

c) Provide sealing surface.

The following Bureau of Indian Standards codes may be referred to while designing slide gates:

IS: 5620-1985 “Recommendations for structural design criteria for low head slide gates”.  

IS: 9349-1986 “Recommendations for structural design of medium and high head slide gates”. 

Commonly used hoists for gate operation 

The mechanical arrangements used for operating the gates are called Hoists, which are classified as follows: 

• Mechanical hoist:
  • Rope-drum type like winches, chain-pulley block, monorail crane, gantry crane, etc.
  • Screw operated type
  • Chain and sprocket type 
• Hydraulics hoist 

The Bureau of Indian Standards code IS 6938 – 1989 “Design of rope drum and chain hoists for hydraulic gates – code of practice” lays down the guiding principles for design of rope drum and chain hoists. The general principle of a rope drum and chain hoist for vertical lift gates is shown in Figure 28. The rope drum arrangement for radial gate is shown in Figure 29. 

The Bureau of Indian Standards code IS 10210 – 1993 “Criteria for design pf hydraulics hoists for gates” provides guidelines for typical hydraulic hoists for gates. A typical arrangement for hydraulic hoist for radial gates is shown in Figure 30 showing the position of the hoist and the gate in open and closed positions. 

Figure 26. Rope Drum Hoist Arrangement for Vertical Lift Gate

Figure 29. Wire Rope Hoist System for Radial Gate

Figure 30. Hydraulic Hoist Operated Tainter Gate