BOfilftG 457 



of the valvo are effected by tappet gear, struck by the head of the piston. In connection 

 with this drill, the following particulars have been obtained : Diameter of cylinder 

 3| inches, diameter of piston-rod 2 inches, dimensions of valve portway 1 |" x |". 

 Length of cylinder in the clear 22 inches, -with attachments 39 inches. Pressure of 

 steam required to drive the drill, 45 Ibs. per square inch. Length of stroke 6 inches, 

 speed of boring bar 280 strokes per minute, consumption of steam or air, forward 

 stroke 81, backward 64, or together 145 cubic inches. Pressure for blow 373 Ibs., for 

 return 231 Ibs. Time required to bore 1- inch hole 1 inch deep in Cornish granite, 

 30 seconds. Strokes required to bore 1 inch deep, 140. Cubic feet of steam or air, 

 consumed per inch of hole in granite, 1 1 ^ths. Advance of machine on screw without 

 change of borer, 18 inches. 



Length of stroke necessary to advance borer 5|ths inches. Number of strokes required 

 to make one revolution of tool 10. For illustration, see Specification No. 2,008, A. D. 

 1872. 



Power Jumper. This machine, the joint invention of Brydon, Davidson and 

 Warrington, consists externally of a long cylinder and valve. The valve and turning 

 gear are automatic ; the advance of the tool is performed by hand. Tho pressure of 

 steam required to work the drill is from 40 to 50 Ibs. per square inch, the number of 

 strokes from 300 to 400 per minute. See Specifications No. 3,507 and 3,921, A. D. 

 1872. 



Darlington's Borer, Fig. 198. The inventor, Mr. Darlington, obtains recipro- 

 catory motion in rock-boring machinery without the intervention of a valve or 

 valvular gear. In one modification a cylinder and motive piston are employed. Tho 

 cylinder itself has an ordinary inlet portway, a long induction passage, and an 

 outlet portway. The depth and length of the motive piston is proportioned to the 

 position of the several portways, so that the induction and exhaust portways are 

 alternately uncovered by the body of the piston which thus distributes the air or 

 steam. The elastic fluid exerts its force continually against the smaller surface of 

 the piston referred to. This piston, in moving in one direction, first covers the exhaust, 

 then uncovers the induction portway and permits the air or steam to exert its force on 

 the opposite side of the piston, which has a superior area to that on which the 

 pressure is constant. In the return movement which follows, the induction portway 

 is first covered, and immediately afterwards the exhaust is uncovered, releasing the 

 superior area of the piston from the pressure, and allowing the constant pressure on 

 the small area to effect the opposite stroke. 



In a second modification, which gives a like action, instead of keeping the fluid 

 pressure continually against the smaller surface of the motive distributing piston, 

 the pressure is alternately admitted to and exhausted from both sides of the piston. 

 To effect this, the piston is made of sufficient length to admit of a groove being 

 turned in it of such a length as to always be in communication with the pressure 

 portway formed about the centre of the length of the cylinder. Two induction 

 passages and two exhaust portways are also formed in the cylinder. The motive 

 piston, in its passage across these said portways, admitting the pressure to one 

 induction portway, communicating -with one end of the cylinder, at tho same time as 

 it uncovers one exhaust portway and releases tho pressure from the opposite end of 

 the cylinder. 



Beyond these two modifications of one and .the same invention, two other modes of 

 distributing the steam or air have been devised. The objects gained by the foregoing 

 method of obtaining reciprocatory motion for rock-boring and coal-cutting machines 

 are (1) There is only one working part used in obtaining tho motion of tho 

 piston,' with its rod attached, both being in one solid piece, without any loose or 

 attached part to bo destroyed by the effect of rapid reciprocation and percussion. (2) 

 Being enabled to use large portways and passages, which are opened and closed 

 quickly, without having any reference to or being dependent on tho movement of a 

 valve, greater rapidity of motion and efficiency of blow are given. (3) Control of 

 speed, weight of blow, and length of stroke given by the machine, and great limit of 

 variation in the range of stroke, total freedom from stoppages due to displacement of 

 valves, as by this arrangement while tho pressure is on the piston can never be in 

 equilibrium, but must start at any part of the stroke. (4) Economy in working, as 

 there is no clearance s^ace to be filled with pressure and exhausted to wasto at every 

 stroke, tho pressure being worked expansively to any degree required. The following 

 are the dimensions of a machine designed to work in ordinary mine levels. Weight 

 of cylinder and piston-rod without frame, 70 Ibs ; length of cylinder over all 14 inches, 

 diameter of cylinder 3 inches, speed 1,000 blows per minute, length of stroke from 

 l to 3 inches, cubic inches of air or steam por stroke 34, number of strokes per cubic 

 foot of steam or air 50, weight of blow exclusive of effect duo to tho weight and 



