LOCK GATES AND VALVES. 195 



forgings, 27^ cents; and the bronze, 35 cents. Of the first-named item there were 

 2,405,000 Ibs., and of the others a total of 169,300 Ibs. The width of chamber is 100 

 feet, with 21 feet of water on the sills, and a lift varying from 18 to 20.8 feet, the 

 largest gate being about 43 feet high, and the smallest about 25^ feet. The cost per 

 square foot was approximately $13.* 



On the German canals just alluded to it is the practice to use wooden gates for 

 locks up to 42 feet in width, and iron gates for greater widths. In Holland the use of 

 wood is limited as a rule to widths of chamber of 60 feet. 



VALVES. 



The regulation of water in the chamber is obtained through valves placed in the 

 gates or in culverts built in the walls and floors for passing the water around or under the 

 gates. Culverts for filling usually discharge through the lift-wall by means of several 

 small lateral openings connected with a large culvert reaching across the lock. This 

 division of the water into small streams emptying near the lock floor causes little dis- 

 turbance to boats. In large locks they are frequently extended along the main walls, 

 instead of being built in the miter-walls, and discharge through openings at right 

 angles to the axis of the chamber. In the lock of the St. Mary's Falls Canal the water 

 flows along culverts under the floor and discharges upward through two hundred and 

 fourteen openings into the chamber. 



The emptying culverts are usually built around the heels of the lower gates, enter- 

 ing from the gate recesses and discharging below the miter-wall into the tail bay. The 

 river-wall culvert sometimes opens directly through the wall into the river below the dam. 



The wickets, or valves controlling the movement of water in the lock, are maneu- 

 vered from the top of the lock wall by machinery connected with the valves through 

 openings in the walls, or by a system of sheaves and chains on the faces of the walls. 



Valves in culverts are very satisfactory, although more expensive to construct 

 and to repair than valves in gates, which are equally satisfactory in operation. They 

 should be used for filling in cases where the lift-wall is above the lower pool and where 

 gate valves would consequently discharge into the air and splash over boats in the 

 chamber. Sometimes, instead of being placed in culverts, they are put in the floor 

 above the miter-sill, and open directly into culverts passing under the latter. 



The entrances to all culverts should be provided with screens of bar iron, about 2\ 

 inches by f inches, hinged on the down-stream side to open like a gate, and latched 

 to the wall. They are needed to prevent debris becoming entangled in the wickets. 



Manholes have been provided in many of the older locks, opening vertically through 

 the wall. In the later ones, however, they have been omitted, as they have not been found 

 of practical use. 



* Annual Report Chief of Engineers, U. S. A., 1895. 



