2^6 DOCK ENGINEERING.
The paddle is slightly larger than the opening—about 6 to 12 indies each
way—and may be either tapering in thickness or with parallel faces. It
is a judicious arrangement to have duplicate paddles, one being actuated
by hand in case of mishap to the other worked by machinery.
Stoney sluices, so-called from the name of their inventor, have the
friction of the bearing surfaces during movement very much reduced by the
employment of rollers. The doors are of steel, and a watertight joint is
formed by the engagement of a rod in a V-shaped groove. Figs. 180 and 181
explain the arrangements adopted.
ly) Fan doors {portes en éventail) are adopted in some instances a >road.
They are in the shape of a right-angled triangle in plan (fig. 182), witha
vertical axis at the corner, formed by the intersection of two plane surfaces
of unequal area. When in position the smaller wing, bearing against a
wood-lined frame, cuts off the culvert connection. To open the gate the
larger wing has to revolve within a cylindrical chamber. A small discharge
Fig. 182. —Plan of Fan Door at Dunkirk.
pipe fitted with a valve serves to set the gate in motion. While the valve
remains closed the up-stream pressure keeps the gate shut. As soon,
however, as the valve is opened the water in the cylindrical chamber escapes,
down-stream pressure is introduced into the chamber, and the difference
causes the gate to revolve on its pivot, in virtue of the unequal areas
exposed.
(3) Other doors or gates are in one plane surface throughout, turning
upon a vertical axis slightly out of centre. By opening a small valve in the
wider panel the pressure on that panel is reduced below the pressure on the
other panel, and the gate revolves so as to set itself in a line with the
stream Closing the valve and giving the gate a slight sideways displace-
ment causes the current to act with greater effect on the larger surface, se
that the gate automatically swings to. It is locked in position by a turn o
the wooden side post.