1550
THEORY AND PRACTICE OF ENGINEERING.
Book II.
Fig. 2867.
PLAN OF GATES.
or when the angle at the base is 35° 16' nearly, and the sally of the gate is or a triflemore than one-third of the breadth of the lock.
The Gates of large Locks , or those at the entrances of docks, as at St. Katherine’s in theport of London , are framed with whole timbers, the uprights and horizontal rails beingsecured to each other bystrong wrought-iron straps.
The planking which coversthe face of the frameworkis placed perpendicularly,and the paddles are workedby a rack and pinion. Theturning or heel-posts areheld in their position byiron ties let into the stone-work.
Some lock-gates havetheir paddles made to openand shut by the movementof a lever, the lower end ofwhich being loaded keepsit always over the aperturein the lower part of thegate: when it is requiredto be moved, the upper partor handle of the lever ispulled back, and the waterforcing its passage through,keeps it open until its weightovercomes the power, and itis balanced back into itsoriginal position.
Fig. 2868. HEEL-POST.
Fig. 2869. section.
Fig. 2870. ELEVATION.
Fig. 2871. section.
The crank and pinion working in a toothed rack are now generally applied to raise thepaddle.
Screws are sometimes used for this purpose, formed of wood, sliding up and down ina rebated frame, fixed in the stone mouth of the conduit or paddle-hole ; the lateralpressure of the water, occasions it to adhere closely to the frame, so that it is not onlynecessary to make it run with the grain of the wood, but also to have considerable powerto move it; this is occasionally effected by means of a long iron lever, with an eye at oneend that spans the square end of the screw and allows a sufficient force to be applied toraise the paddle.
There are several applications of the screw, one of which, as used at the gates of Dunkirk, isvery simple, and was for a long time adopted throughout Europe . To overcome the hydro-static pressure and friction, at the mouth of the paddle-hole was a horizontal circular opening,within which was inserted an open cylinder of wood or iron ground to fit it, which could be