LOCK GATES AND VALVES. 185 



metal throughout. This will necessitate the use of buckled plates, which, though more 

 expenisve than flat plates, arc much cheaper in the end, as they will carry a much 

 heavier load. They should be f inch thick at the bottom, or heavier if obtainable, 

 diminishing to \ inch for the upper panels. All shop-work should be made as simple 

 as possible, since curving or bending in order to save metal frequently costs more than 

 the material it saves. 



The calculations for the beams are similar to those before given, and careful atten- 

 tion must be used in securing proper connections between the various parts. The 

 diagonal suspenders used on wooden gates to uphold the toe are unnecessary on 

 metal gates, as the skin-plates supply all the stiffness required to prevent sagging. 

 Their omission is also preferable for navigation, as craft entering or leaving a lock 

 occasionally rub along the gates, and the down-stream diagonal is liable to be bent by 

 the impact. 



Where the gates support considerable pressure it is sometimes necessary to plane 

 off the ends of the lower beams so that they will have a close bearing against the heel- 

 and toe-verticals, and thus transmit the compression from the other leaf. Stiffeners 

 may also be used for this purpose. 



The most economical shape for the beams for locks up to 55 feet in width, with 

 ordinary lifts, consists of I beams, which can now be obtained in depths of 24" and 

 under. They are cheaper than built-up girders, as they require less shop-work, and 

 where the section has to be reinforced, cover-plates can be added to the flanges. 

 Holes should be provided in the webs for the drainage of rain- and flood-water. 



The heel- and toe-posts are usually provided with timbers bolted to them and shaped 

 to fit the hollow quoins and the miter. This is an excellent practice, as the wood 

 provides a tight and elastic cushion, and where the quoins are of masonry it will wear 

 itself into fitting any irregularities, and where they are of cast iron it can be planed off 

 to fit imperfect joints and alignment. 



The wooden heel is objectionable, however, on the point of difficulty of renewal, 

 and care must be taken in designing the gate to see that this is reduced to a minimum. 

 Where this is done timber will generally be found preferable to a metal heel cushion, 

 owing to the difficulty of adjusting the latter to the unavoidable imperfections of 

 construction. 



It has been proposed where a metal cushion is employed to use strips of a soft 

 metal, such as lead, set vertically in slots in the cast-iron pieces. The lead would then 

 permit trimming to fit inequalities of the quoin.* 



Where wooden cushions are used, they should be cut in two just below the pool 

 level, and the portions above, which will rot first, can then be removed without dis- 

 turbing the parts below water. 



The contact with the miter-sill may be formed by the bottom beam of the gate, 

 or an additional wooden cushion may be used. 



* Proceedings American Society of Civil Engineers, April, 1902. 



