LOCK GATES AND VALVES. 189 



pipe and closing the ends with cast plugs, in which are inserted short lengths of i-inch 

 rod to serve as journals. The journal-boxes should be arranged so that the rollers 

 can be removed when desired. 



Each gate should be provided with a hand-railing, placed on the upper side so as 

 to be out of the way of boats. It may be made of i^-inch gas-pipe, with uprights of the ' 

 same size, fitting loosely into cast-iron sockets bolted to the gate. On the approach of 

 floods the railing can then be lifted out in one piece and removed. 



Miter Joint. The upper side of the miter or toe, both in wooden and in metal 

 gates, should be beveled off for about a third of its width, so that the actual surface of 

 contact when mitered will fall upon the lower two-thirds. This is done in order to throw 

 the compression from the end reactions into the down-stream sides of the beams, thus 

 relieving the tension existing in them from the direct loading, and at the same time 

 avoiding increasing the compression which exists from the same cause in their up-stream 

 sides. 



Alignment. The usual practice is so to place the gate in its recess that its face will 

 be from 6 to 12 inches back from the face of the chamber when the gate is open. This 

 is done to prevent boats from striking it, but unless fenders are provided extending out 

 to the chamber line, boats will strike and break off the edges of the square and of the 

 hollow quoins. These fenders should always be placed horizontally, not vertically. 



In other cases the gate itself is made flush with the chamber and acts as the fender. 

 Either way is satisfactory in practice, since craft rarely cause any injury to gates when 

 they glance against them, if the diagonal straps and other projections have been pro- 

 vided with the proper fenders. 



Bumping-blocks should be provided on the up-stream side of the toe of each gate, 

 one near the top, the other near the bottom. Their object is to hold the gate parallel 

 with the recess- when open, and they must therefore be of a width such that when the 

 gate is in this position the blocks will touch the masonry. 



Gates for Concrete Locks. The heels of gates for concrete locks should be designed 

 so that a certain amount of trimming can be secured without difficulty, as in this class 

 of masonry it is not practicable to secure as accurate a hollow quoin surface as can be 

 obtained in a lock of cut stone. 



Life and Care of Gates. The life of a wooden gate in this country is from ten to 

 twenty years, the latter being a limit which is very rarely reached. However, as the 

 submerged part of a gate is not as subject to deterioration as the upper part, the leaf is 

 frequently repaired by rebuilding the part above water, and retaining the submerged 

 portion, which will usually be ready for renewal when this second top has become 

 decayed. On the North German canals the life of a wooden gate is given as from 17 to 

 38 years, with an average of 25 years, the same average being given for the wooden 

 gates at certain French harbor locks. An example is to be found of a wooden gate at 

 Antwerp still in good condition after 40 years of service, the timber being creosoted fir, 

 while gates of Demerara greenheart at some of the English locks have lasted for more 



