LOCK GATES AMD VALVES. 



width, and has a length of 118 feet. They are built of steel, trussed like a bridge. The 

 movements are made with heavy chains wound upon drums by steam-power, and con- 

 siderable difficulty has been encountered in some cases with the breaking of chains, 

 and also with the breaking of the axles upon which the gates rest. The recess, which 

 is 1 20 feet long, reaching back into the river-bank, is also a source of considerable 

 expense in construction, and the accumulation of debris or of ice in it is an annoyance 

 at the time of locking. These difficulties are occasionally increased by the breaking 

 of parts under water, so that this style of gate, while of ingenious design, is still of 

 uncertain utility. 



Tumble-gates. A gate with horizontal axis, known as a " tumble "-gate, forms a 

 type which has long been in use on the Erie Canal and in Europe. These gates con- 

 sist of a single leaf hinged to the lock floor, the boats passing over it when it is lowered. 

 They are maneuvered by chains passing over crabs on the walls. 



Hydraulic Gates. It has been suggested to apply the principles of bear-trap and 

 drum dams to lock gates, in order to secure a gate which could be operated automati- 

 cally, and several ingenious devices have been proposed for such an application. 

 Gates of the former type are in use at the lock of the Sandy Lake Dam, in Minnesota, 

 and are 40 feet in length with a rise of 13 feet. They were built in 1895, and serve as sluice- 

 gates also. An upper gate of the Chittenden drum type is in existence at Lock No. 2, on 

 the Mississippi River, near St. Paul, having been put in about 1901. These are believed 

 to be the only locks where hydraulic gates are in use. 



Automatic gates which could be raised and lowered easily would possess several 

 advantages over mitering gates, such as permitting the washing out of deposit from 

 the chamber and entrances, etc., but they would be more difficult to keep in proper 

 working order, and more expensive to repair, owing to the greater number of parts 

 which would be always under water, and it may be doubted whether they will have 

 any extended application. 



Calculations for Lock Gates. General. In the following calculations only those types 

 of gates will be examined which fall within the ordinary practice of the engineer. The rarer 

 types, such as arched gates, have been discussed in other works.* 



The simplest form of gate is that of a beam placed squarely across the lock cham- 

 ber, and supported against the masonry at each end. This style has been used on 

 canal locks, as before described. The strains in such gates are those of a simple beam, 

 or, where the gate is large enough to require truss framing, they can be analyzed graph- 

 ically or by moments, in the methods employed for framed structures supporting uni- 

 form loads. 



* See "Mitering Lock Gates," First Lieutenant Harry F. Hodges, Government Printing Office, Washington, 

 1892. An analysis of the arched gates of the St. Mary's Falls Canal is published in the Annual Report of the Chief 

 of Engineers, U. S. A., 1895, Appendix LL; and a full list of literature on Lock Gates will be found in the Report 

 of the Deep Waterways Commission, Washington, 1900, pp. 200-207. 



