HYDRAULIC CRANES 



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1 The absence of any sensible elasticity in water renders the motions resulting from 

 its pressure capable of the most perfect control, by means of the valves which regulate 

 the inlet and outlet passages of the machines ; but this very property, which gives 

 so much certainty of action, tends to cause shocks and strains to the machinery, by 

 resisting the momentum acquired by the moving parts. Take, for example, the caso 

 of an hydraulic crane, swinging round with a load suspended on the jib, the motion 

 being produced by the water entering on one side of a piston and escaping from the 

 other. Under such circumstances, if the water-passages be suddenly closed by the 

 regulating valve, it is obvious that the piston, impelled forward by the momentum of 

 the loaded jib, but met by an unyielding body of water deprived of outlet, would be 

 brought to rest so abruptly, as to cause, in all probability, the breakage of the machine. 

 So also, in lowering a heavy weight with considerable velocity, if the escape-passage 

 be too suddenly closed, a similar risk of injury would arise from the abrupt stoppage 

 of the weight, if a remedy were not provided ; but these liabilities are effectually 

 removed by applying, in connection with the water-passages to the cylinder, a small 

 clack-valve, opening upwards against the pressure into the supply-pipe, so as to 

 permit the pent-up water in the cylinder to be pressed back into the pipe whenever it 

 becomes exposed to a compressive force exceeding the pressure on the accumulator. 

 By this means all jerks and concussions are avoided, and a perfect control over the 

 movement of the machine is combined with great softness of action. 



' With regard to the kind of valves used for water-pressure machines, I find that 

 either lift-valves or slide-valves may be effectually applied, and kept tight under 

 heavy pressures, provided that sand be excluded from the water, and the valves be 

 made of proper material. 



'In cases where a more prolonged movement is required than multiplying sheaves 

 will conveniently afford, I employ rotative machines of various constructions. For 

 heavy-pressures, such as an accumulator affords, an arrangement consisting of three 

 plungers, connected with a triple crank, and bearing a general resemblance to a three- 

 throw plunger pump, is well adapted for the purpose. The admission and exhaust 

 valves are mitred spindles, pressed down by weights and levers, and lifted in proper 

 rotation by cams fixed for that purpose upon a separate shaft ; and these valves are 

 associated with relief-clacks, to obviate the concussion which would otherwise be liable 

 to take place at the turn of each stroke. 



' The liability of water-pressure machinery to be deranged by frost has often been 

 adduced as an objection to its use ; and upon this point I may observe first, that I 

 have never experienced any interference from this cause when the machines were 

 placed, as they generally are, beneath the surface of the ground, or within a building ; 

 and secondly, that when they are unavoidably exposed, all risk may be prevented by 

 letting out the water in frosty weather whenever the machines cease working. 



When the moving power consists of a natural column of water, the pressure rarely 

 exceeds 250 or 300 feet, and in such cases I have employed for rotative action a pair 

 of cylinders and pistons, with slide-valves, resembling in some degree those of a high- 

 pressure engine, but having relief -valves, to pre- 

 vent shock at the turn of the stroke. Fig. 1173 

 shows a slide-valve adapted for the turning appa- 

 ratus of a crane, but the relief -clacks of which are 

 equally applicable to a water-pressure engine of 

 the construction in question. Two of these clacks 

 open against the pressure in the supply-pipe, so as 

 to afford an escape for the water, which would 

 otherwise be shut up in the cylinder when the 

 exhaust port closes, and the other two communicate 

 with the discharge-pipe, so as to draw in a portion 

 of waste water to fill up the small vacancy which 

 would otherwise be left in the cylinder on the 

 closing of the admission port. A, supply pipe ; B, 

 exhaust pipe ; c c, pipes to cylinder ; D D, clacks 

 opening against pressure ; E E, clacks opening from 

 exhaust. About four years ago I constructed four 

 hydraulic engines upon this principle at Mr. Beau- 

 mont's lead mines in Northumberland, at the in- 

 stance of Mr. Sopwith, Mr. Beaumont's well-known 

 agent, and two more have recently been added at 

 the same place. They are used for crushing ore, for hoisting materials from the 

 mines, for pumping water, and for driving a circular saw and other machinery. See 

 HYDRAULIC MACHINERY, FOR MINES. 

 ' If in progress of time railways should be generally extended into mountainous 



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