In the following sections some broadly valid ranges of heads
and spans for some of the most frequently used types of gates are given.
There are, however, several outstanding examples of large span or high-
head gates considerably exceeding these parameters particularly in
modern flood control schemes and surge barriers where special types of
gates are also often used (see Section 6.4).
Because of the multitude of their functions and sizes there is great
scope for innovation in gate and valve design both in details (e.g. seals,
trunnions), as well as in conceptual design (automatic level control by
hinged flap gates, gates and valves used in water distribution systems,
‘hydrostatic’ gates etc.).
Both crest gates and gates in submerged outlets require provision for
emergency operation and maintenance. Emergency closure gates, mainte-
nance gates, stop-logs, grappling beams, rail mounted gantry cranes,
screens and their cleaning devices (in case of submerged gates) are some
of the necessary appurtenances. For further design and construction
details of various types of gates and valves see Leliavsky (1981), Zipparo
and Hasen (1993), Erbisti (2004) and particularly Lewin (2001).
6.2 Crest gates
6.2.1 Pressure transmission
The basic feature of the structural design of crest gates is the method used
for transferring the pressure acting on them.
- Pressure transmission to piers and abutments is used by plain vertical
lift gates and stop-logs, radial gates and roller gates; the gates may be
designed for flow over or under them or for a combined flow con-
dition.
- Pressure transmission to the gate sill is used, for example, by sector
(drum) gates (with upstream or downstream hinge), roof (bear-trap)
gates, pivot-leaf (flap) gates, roll-out gates, and inflatable gates.
- Pressure transmission both to piers and sill, e.g. some types of flap
gates and floating (pontoon) gates.
6.2.2 Plain gates
Plain (vertical lift) gates, designed as a lattice, box girder, a grid of hori-
zontal and vertical beams and stiffeners, or a single slab steel plate, may
consist of single or double section (or even more parts can be involved in
268 GATES AND VALVES
