CBANEB 



758 



performed by means of chains gearing with a chain wheel fixed on the 

 foundation plate. 



There are two racking cylinders R, with a six-fold multiplying motion, 

 one hoisting cylinder II, with an eight-fold multiplication, and two slewing 

 cylinders S, with a two-fold multiplication, the valves being so placed that 

 one man has full control over the whole crane. 



The illustration shows details fairly well, and is self-explanatory. 



For comparatively small powers and lifts these cranes may be direct- 

 acting, such an one, suitable for loads up to two tons, and for lifts up to 

 about 6 feet, being illustrated in Fig. 370. 1 Here the lifting hook is 

 attached directly to a car- 

 riage running along the 

 jib, which is itself raised 

 and lowered by a direct - 

 acting hydraulic cylin- 

 der sliding between the 

 cheeks of the mast and 

 working upon a hollow 

 steel ram forming the 

 bottom centre of the 

 crane. For smaller 

 loads and lifts the lift- 

 ing cylinder may itself 

 be suspended from the 

 travelling carriage, the 

 hook being attached to the ram, and pressure water being conveyed to 

 the cylinder by a walking pipe. 



With the hydraulic crane the speed of the lifting hook may be adjusted 

 up to about 6 feet per second. 



Dock Cranes. Fig. 371 2 shows the general arrangement of a movable 

 hydraulic luffing crane having a lower power of 15 tons and a maximum 

 power of 30 tons. This crane has a lift of 66 feet and the jib has 

 39 feet maximum and 20 feet minimum rake. 



Fig. 372 shows a type of balanced jib luffing crane, 3 as built for coaling 

 purposes. The jib has an extended end to which are attached the counter- 

 balance weights and tie rods. The lower ends of the tie rods are attached 

 to a travelling crosshead actuated by the rams of the luffing cylinders and 



1 By Messrs. The Hydraulic Engineering Co., Ltd., Chester. 



a By courtesy of Messrs. Sir W. G. Armstrong, Whitworth & Co., Ltd. 



a By courtesy of Mr. Arthur Musker, M.I.C.E. 



H.A. 3 c 



FIG. 370. Direct-acting Wall Crane. 



