Aug. 22, 18e4.] 



* KNOWLEDGE . 



159 



pipe and beneath the piston, 5, being suddenly reduced, the 

 piston falls, and by so doing shuts otl' both the reservoir 

 from the main pipe E and the cylinder from the exhaust 

 port D ; at the same time the passage from the reservoir to 

 the cylinder is open, and air passing from the former to the 

 latter, the brakes are applied. 



Fig. 2. 



For the purpose of graduating the brake with the 

 greatest nicety, that is to say, normally ■nhen approach- 

 ing a station, a small valve, 7, is introduced into the 

 slide-valve, 6. The action is as follows : — Upon a slight 

 reduction of pressure in the brake-pipe being made, the 

 piston, 5 — having a limited movement, without affecting 

 the slide-valve, 6 — will descend, thereby closing the feed- 

 groove d, at the same time unseating the valve, 7, which 

 thus opens the passage e. The slide-valve, 6, then moves 

 until the passage e opens into port a, leading to the brake- 

 cylinder, the communication from which to the exhaust is 



at the same time cut ofl". The further downward move- 

 ment of the slide-valve, 6, is arrested by the decrease of 

 pressure above the piston, caused by the air flowing into 

 the brake-cylinder. So soon as the pressure in the reser- 

 voir is thus reduced a little below that in the brake-pipe, 

 the piston, 5, moves up of its own accord, and closes the 

 valve, 7, while the slide-valve, 6, retains its position. By 

 simply regulating the reduction of pressure in the brake- 

 pipe, and causing the motion of the piston and graduating- 

 valve, 7, to be repeated, the driver can gradually introduce 

 any desired pressure into the brake-cylinder from zero up 

 to full power. However, if a considerable reduction of 

 pressure in the main pipe is suddenly made, the piston, ."), 

 is seated on the leather gasket, 10, while the port a is 

 entirely uncovered, and the brakes are thus applied witli 

 full force. 



To release the brakes, air is again admitted from tha 

 main reservoir to the brake-pipe Viy means of the driver's 

 valve. This store of power acting against the reduced 

 pressure in the small reservoirs, forces the piston, 5, into 

 the position shown, thus permitting the air in the brake- 

 cylinders to exhaust, while at the same time the reservoirs 

 are recharged. 



To prevent such application of the brakes as might 

 result from ordinary leakage in the brake-pipe, a small 

 hole runs from the face of the slide-valve t() the passage 

 e. In such a case a piston and slide-valve descend 

 very slowly, and as the port a is open both to the 

 exhaust cavity, h, and the leakage hole during the first por- 

 tion of the stroke, air from the reservoir is able to escape 

 by this means into the atmosphere, instead of passing into 

 the brake-cylinder. The reduction of ))ressure thus caused 

 above the piston, as already explained, prevents the slide- 

 valve from moving far enough to close the communication 

 between the port a and the exhaust cavity b. 



The only moving parts of the triple valve (an ordinaTij 

 pislon and slide valve moving together as one piece) do not 

 make as many motions in fifteen years as are made by the 

 piston and slide-valve of the locomotive in one day ; hence 

 their durability is beyond question, and this is confirmed 

 by many years' experience. 



A stopcock is placed in the branch-pipe (between E 

 and F, Fig. 1) for the purpose of closing the connection 

 with the triple valve on anyone vehicle without interfering 

 with the operation of the brakes upon any other. A 

 release valve (inserted in the tube connecting F with H, 

 Fig. 1), operated by hand from either side of the train, 

 may be opened to allow the air to escape direct from the 

 brake-cylinder if necessary. 



The leservoir space is about five times that of the braka- 

 cylinder, consequently, a reduction of 20 per cent, in the 

 brake-pipe pressure fully applies the brake, each pound 

 reduction of pressure in the brake-pipe producing several 

 pounds per square inch in the biake-cylinder. By the 

 action of tlie triple valves, moreover, the brakes cannot be 

 released without re-charging the small reservoirs, and 

 owing to these features it has been found in working that 

 the store of power is practically never-faiiing. 



It is evident from what has been said that if by any means, 

 air is allowed to escape from the main-pipe, the brake must 

 be brought into action, whether it is required or not. This 

 fact constitutes the one great recommendation of the brake 

 to the travelling public, which, I appiehend, embraces 

 the va-^t majority of our countrymen. We are not so 

 much inter.-sted in bone-shaking stoppages at stations, 

 as we are in being arrested on what might otherwise be 

 the highroad to destruction. The brake may be relied 

 upon to o[)erate within 200 yards when running at fifty 

 miles an hour. It is not, however, in such cases only that 



