6.3 High-head gates and valves
6.3.1 GeneralHigh-head (submerged) gates and valves transmit the load to the
surrounding structure either directly through their support, e.g. plain (ver-
tical lift), radial, or ring follower gates, or through the shell encasing the
valve. The most common valves of the latter type are non-regulatingdisc
(butterfly) valves (turning about a horizontal or vertical axis), cylindrical
or sphere (rotary) valves. The main advantage of the latter is the clear
water passage when fully open and hence a very low head loss coefficient,
but their cost is higher than that of butterfly valves. The most frequently
usedflow regulatingvalves in closed pipe systems are sphere valves or
pressure reducing valves. For terminal discharge regulation a frequent
choice are needle, tube, hollow-jet and particularly Howell–Bunger (fixed-
cone dispersion) valves.
6.3.2 High-pressure gatesPlain (vertical lift)gates (Fig. 4.19) are sliding, wheeled or moving on
rollers or caterpillars. The load on them may reach 3000–4000 kN m^1 with
heads up to 200 m and gate areas up to 100 m^2 (usually 30–50 m^2 ). For
optimum conditions it is best to contract the pressure conduit upstream of
the gate and to provide deflectors downstream to aid aeration as an anti-
cavitation measure (see also Section 4.7.3). The conduit face downstream
of the gate slots should be protected against cavitation in the same way as
for crest gates (see Section 6.2.2). Even better protection is provided for
non-regulating lift gates by ring followers, which close the gate grooves
and ensure a smooth passage for flow through the fully opened gate. Other
developments of this type of ring follower gate are paradox and ring seal
gates (Zipparro and Hasen, 1993).
Radialgates are normally hinged downstream (Fig. 4.21), but are some-
times used in the reversed position with arms inside or, more frequently,
outside the conduit at the end of which the regulating gate is installed.
A special feature of some high-head Tainter gates is the use of eccen-
tric trunnions (Buzzel, 1957) which permit a gap to be formed between the
seals and the seal seats before opening the gate so that only moments caused
by the gate weight and hinge friction have to be overcome. This type was
used, for example, at the Dongjiang dam for gates with span 6.4 m and
height 7.5 m operating under a head of 120 m (Erbisti, 1994).
Cylinder gates with all hydraulic forces counterbalanced are fre-
quently used in tower type intakes; gate diameters up to 7.00 m with
maximum heads about 70 m have been used.