PNEUMATIC DISPATCH 



62O4 



PNEUMATIC DISPATCH 



Fig. 2 



done with the larger tools, which 

 are able to close rivets up to 1J in. 

 diameter very quickly, and arc 

 most useful in 

 positions 

 where hydrau- 

 lic riveting is 

 impracticable 

 or over-costly. 



Modified 

 forms of ham- 

 mers are em- 

 p 1 oy ed in 

 f o u n dries to 

 ram the sand 

 in moulds, 

 and in ma- 

 sons' yards 

 for chipping 

 stone. 



PNEUMATIC 

 HOISTS. These 

 are of great 

 use in work- 

 shops and 

 foundries for Vl^ 



lifting heavy Pnfl umatic Appliances, 

 work, cast- Sectional diagram of 

 ings, etc. Fig. pneumatic hoist. See 

 2 is a sectional text 



view of a vertical oil-controlled 

 hoist, adapted to be slung from a 

 crane by eye E. Chamber A con- 

 tains oil, some of which, when the 

 hook is pulled down, passes through 

 the non-return valve V and the 

 central fixed pipe into the hollow 

 piston-rod. To raise the load, air is 

 admitted to the under side of the 

 piston through valve V 2 , and the 

 pulley P is rotated by a rope or 

 chain, opening the small needle 

 valve shown, which allows the oil 

 to escape gradually into A. Hoists 

 of this kind are constructed to deal 

 with loads up to five or more tons. 



PNEUMATIC ROCK DRILLS. These 

 are generally larger and heavier 

 than pneumatic hammers, are 

 carried on tripods, standards, 

 crossbars, or other supports, and 

 have a mechanism for feeding the 

 drill forwards and rotating it 

 slightly between strokes. The 

 drill is either struck by a loose 

 hammer piston or reciprocated by 

 the piston through a piston-rod 

 and chuck. Drills of the second 

 type have moving air-valves. 



Figs. 3 and 4 illustrate one type of 

 Ingersoll-Rand drill and the action 

 of the very ingenious " butterfly " 

 valve used. The valve itself con- 

 sists of a cylindrical trunnion or 

 body, integral with two flat wings, 

 one on either side, ground to a 

 perfectly true surface. The trun- 

 nion rests in bored steel bush- 

 ings hi a valve chest with a free 

 working fit. The wings are able to 

 oscillate slightly about the trun- 

 nion as centre. In Fig. 3 the 

 piston is about to make an out- 

 ward stroke. The upper wing of V 



has been driven over to the right, 

 closing supply port S 1 and opening 

 port S 1 , as well as exhaust port 

 W. Air enters the cylinder through 

 SS* and drives the piston forward, 

 while the exhaust passes out 

 through EE 1 and E 1 . As soon as 

 P uncovers port EE 2 live air 

 reaches port E*, and its pressure at 

 this point on the lower wing balan- 

 ces the pressure on the other wing. 



The valve is now in equilibrium, 

 but still kept stationary by the 

 rush of air at S until the piston 

 covers EE 1 and compresses the air 

 in front of it. The pressure, com- 

 municated through SS 1 and S 1 

 to the valve, throws the latter into 

 the position shown in Fig. 4. The 

 piston then travels in the opposite 

 direction, but with less force than 

 during the out-stroke, as its front 

 end has a smaller area exposed to 

 the air. The drill delivers 600 

 blows a minute. Rotation of the 

 drill is effected by a bar B with 

 external rifle grooves, which pro- 

 jects centrally into and engages 

 with the piston. The head of the 

 bar Is controlled by a ratchet R and 

 pawls which allow it to rotate 

 slightly during an out-stroke of the 

 piston, but prevent the piston 

 twisting it while moving inwards. 

 Consequently the piston and the 

 drill make a complete revolution 

 every few strokes. 



Small portable air-motors, en- 

 closed in dust-proof cases provided 

 with handles, control-valve, and 

 breast-rests or screw-feed gear, 

 have been generally adopted in 

 engineering shops for drilling, 

 reaming, and tapping holes, and 

 expanding boiler tubes. 



PNEUMATIC PAINTING MACHINES. 

 The application of paint, varnish, 

 oil, etc., in the form of a fine air- 

 blown spray has certain advantages 

 over brush-work. The covering 

 speed is much higher ; the material 

 is deposited more evenly on irre- 

 gular surfaces. The air is led from 

 a small compressor, or other source 

 of supply, through flexible tubing 

 to a portable air-tight vessel 

 which contains the pot holding the 

 paint and serves also as air-reser- 



Fig. 4 



Pneumatic Appliances. Diagrams 

 illustrating construction of a pneu- 

 matic rock drill. See text 



voir. The spraying nozzle, con- 

 nected with the container by two 

 flexible pipes one for the paint 

 and the other for air is controlled 

 by a thumb valve. When the valve 

 is depressed, paint is forced by air- 

 pressure through a fine jet and 

 meets a stream of air issuing from 

 another jet, by which it is atomised 

 and blown on to the work. With a 

 paint-sprayer 700-1,000 square ft. 

 can be coated an hour. 



SUBSIDIARY USES. Compressed 

 air has been used for the firing of 

 large guns. The first successful 

 application was by Mefford in 

 1883, who used pressures up to 

 500 Ib. per sq. in. E. L. Zalinski, 

 of the United States artillery, in 

 1888 produced his so-called dyna- 

 mite gun, in which pressures of 

 1,000 Ib. per sq. in. were used. 

 Several of these guns were mounted 

 on the coastal defence works of 

 New York and San Francisco, but 

 the system did not come into 

 general use. ' 



In grain elevators _ the force of 

 air suction is made use of, the 

 grain being drawn through flexible 

 pipes. In pneumatic bells pipes of 

 narrow bore replace the usual 

 electric wires. The pressure of the 

 push button forces a current of air 

 along the pipes and actuates the 

 bell hammer. Pneumatic clocks 

 are a system of synchronous clocks 

 which are connected with the cen- 

 tral controlling clock by com- 

 pressed air. From the central clock 

 air impulses are sent at regular 

 intervals through the connecting 

 tubes, expanding a bellows on each 

 dial and moving the hands. Pneu- 

 matic tires are rubber tubes which 

 are kept inflated by air under 

 pressure. See Compressed Air ; Tire. 



Pneumatic Dispatch. Convey- 

 ance of material along tubes by 

 air pressure. The transmission of 

 papers and other articles through 

 pneumatic tubes in carriers was 

 first adopted for public purposes in 

 1853, when a tube 3 ins. in dia- 

 meter and 220 yds. long was laid 

 between the London Stock Ex- 

 change and the International Tele- 

 graph Company's Offices. Since 

 then pneumatic dispatch has been 

 introduced into many postal offices, 

 business premises, stores, hotels, 

 etc. ; and many 

 =^ hundreds of miles 

 Fig. 3 of tubes are now 

 in constant use. 



A carrier is moved through a 

 tube either by creating a partial 

 vacuum in front of it, while ex- 

 posing its rear end to full atmo- 

 spheric pressure, or by introducing 

 air at above atmospheric pressure 

 behind it. Where a single tube 

 only is used between the two 

 terminals, the carrier is blown in 



