DOCK GATES. 227 



ram is of iron, cast vertically in one length, and is firmly guided 

 and fixed to the gate by a forged-steel cross-head and coupling- 

 pin. Trunnions are cast on the cylinders, projecting above and 

 below, and pivot in saddle-bearings, which also have trunnions 

 on their sides, and these pivot in bearings fixed to the side walls 

 of the ram-chamber, thus permitting the cylinder to oscillate 

 horizontally and vertically. The hydraulic rams are of sufficient 

 strength to resist shocks of waves and to hold the gates rigidly 

 during movement. In the passage gates, the ram is attached to 

 a radius arm near the top, with a slide against the back of the 

 gate, the other end of the arm working on a pin in the holding- 

 down bracket over the top of the heel-post. As the power 

 required is less, the diameter of the piston is only 2 feet 1-J 

 inches, and that of the ram 1 foot 6 inches, with a stroke of 

 16 feet 7 inches. The cylinder for the passage-gate machine is 

 of iron, cast in one piece, and tested to a pressure of 2400 Ibs. 

 per square inch. 



"A combined regulating and escape valve 1 is fixed to each 

 machine, in order to reduce the pressure of 700 Ibs. per square 

 inch to any degree below 500 and 100 Ibs. The pressure usually 

 employed for the entrance-gate rams is 250 Ibs., and the ordinary 

 time occupied in opening the gates is one minute and a half, 

 and the same in closing. At the passage, the full accumulator 

 pressure is admitted to the ram cylinders, and the time occupied 

 in opening is less than one minute, and the same in closing." 



One great advantage attaching to this method of moving 

 gates is that there are no chains to interfere with the fairway 

 of the entrance. 



A drawback in connection with gates is the difficulty and 

 cost of efficient inspection and repair. It is absolutely necessary 

 for their proper preservation that they should be periodically 

 examined and painted. As a general rule, this is done by lifting 

 and docking the gates, or provision may be made for enclosing 

 them temporarily by forming stops in the masonry of the 

 entrance, in which caissons can be placed; by this course, the 

 gates can be dried and thorough examination and repairs effected 

 in position. 



Rollers. 2 To take the weight of the gates and relieve the 

 strain on the side walls, it is usual to place a truck or bracket 

 carrying a roller or slide under the gates. During the operation 

 1 M.P.I.C.E., vol. ci. 140. 2 Ibid., vol. Iviii. p. 156. 



