DOCK GATES. 



225 



A very convenient and efficient method 1 of manipulating 

 dock gates is shown by Figs. 211, 212. In this arrangement, 

 a single hydraulic engine is attached to a crab having two 

 cupped drums, either of which can be thrown out of, or into, 



Closing 

 Ram 



FIG. 210. 



gear by a clutch, leaving the other free for overhauling. This 

 one engine, with its double crab, serves for two chains, and these, 

 instead of descending in chainways through the masonry, are 

 led along the top of the gates, as shown in Fig. 212, in which 



FIG. 211. 



FIG. 212. 



A is the chain for opening, and B the chain for closing. The 

 opening chain passes over a pulley at C, and then descends 

 verticall} 7 by the side of the gate to a point corresponding to 

 that at which the end of the chain is usually attached; at that 

 1 M.P.LC.R, vol. L p. 83. 



Q 



