Gates and Valves for Flow Control (Part - 2) - Civil Engineering (CE) PDF Download

Classification of gates based on location of opening with respect to water head 

The different types of gates used in water resources projects may be broadly classified as either the Crest or Surface type, which are intended to close over the flowing water and the Deep-seated or Submerged type, which are subjected to submergence of water on both sides during its operation. The different types of gates falling under these categories are as follows:

Crest type gates 

1. Stop-logs/flash boards A log, plank cut timber, steel or concrete beam fitting into end grooves between walls or piers to close an opening under unbalanced conditions, usually handled or placed one at a time (Figure 1). Modern day stop-logs consist of steel frames that may be inserted into grooves etched into piers and used during repair / maintenance of a regular gate (Figure 2). The stop logs are inserted or lifted through the grooves using special cranes that move over the bridge.

Figure -1. Stoplogs (Needles) Inserted Within Grooves Of Adjacent Piers

2. Vertical lift gates These are gates that moves within a vertical groove incised between two piers (Figure 3). The vertical lift gates used for controlling flow over the crest of a hydraulic structure are usually equipped with wheels, This type of gate is commonly used for barrages but is nowadays rarely used for dam spillways. Instead, the radial gates (discussed next) are used for dams. This is mostly due to the fact that in barrage spillways, the downstream tailwater is usually quite high during floods that may submerge the trunnion of a radial gate. 

3. Radial gates These are hinged gates, with the leaf (or skin) in the form of a circular arc with the centre of curvature at the hinge or trunnion (Figure 4). The hoisting mechanism shown is that using a cable that is winched up by a motor placed on a bridge situated above the piers. Another example of radial gate may be seen in Figure 2, where a hydraulic hoisting mechanism is shown.  

4. Ring gates A cylindrical drum which moves vertically in an annular hydraulic chamber so as to control the peripheral flow of water from reservoir through a vertical shaft (Figure 5). 

5. Stoney gate A gate which bears on roller trains which are not attached to the gate but in turn move on fixed tracks. The roller train travels only half as far as the gate (Figure 6). This type of gate is not much in use now. 

6. Sector gates A pair of circular arc gates which are hinged on vertical axis in a lock (Figure 7). These gates are used in navigation locks where ships pass from a reservoir with a higher elevation to one with a lower elevation.

7. Inflatable gates These are gates which has expandable cavities. When inflated either with air or water it expands and forms an obstruction to flow thus effecting control (Figure 8). Though these gates have not been commonly used in our country, it is used quite often in many other countries because of its simplicity in operation – However, they suffer from possible vulnerability from man-made damages. 

FIGURE 8 : INFLATABLE GATE

8. Falling shutters Low head gates installed on the crest of dams, barrages or weirs (Figure 9) which fall at a predetermined water level. Generally these are fully closed or fully open, that is, fallen flat, which are shown to operate using a hoist. However, in some weirs, falling shutters have been provided earlier that are manually operated. In many of the older weir installations constructed during the preindependence period were equipped with falling shutters, some of which are still in use today (Figure 10). 

Figure 9. Automatic falling shutter

9. Float operated gates A gate in which the operating mechanism is actuated by a float that is pre-set to a predetermined water level (Figure 11). These may be used as escape in canals or even in dams to release water if it goes above a certain level considered dangerous for the overall safety of the project. 

Figure 11. Automatic Float Operated Radial Gate

10. Two-tier gates A gate used in two leaves or tiers which can be operated separately, but when fully closed act as one gate. These types of gates are used to reduce the hoist capacity or the lift of the gate (Figure 12). Such a gate has been installed in the canal head regulator of the Farakka barrage.