Diseases of the air brake system; their causes, symptoms and cure . gency application. If this sticking is accompaniedby a violent blow from the exhaust when an attempt torelease is made, it is a sure indication that the emergency-valve (Plate 17, No. 10) did not go back to its seat prop-erly after the application, and something must be done tomake it do so. Dirt lodging on the seat as described justabove may be the cause, or it mory be some defect in theapparatus itself, such as the spring (No. 12, Plate 17)being broken or very weak, or some binding of the piston(8). The author has a very dis
Diseases of the air brake system; their causes, symptoms and cure . gency application. If this sticking is accompaniedby a violent blow from the exhaust when an attempt torelease is made, it is a sure indication that the emergency-valve (Plate 17, No. 10) did not go back to its seat prop-erly after the application, and something must be done tomake it do so. Dirt lodging on the seat as described justabove may be the cause, or it mory be some defect in theapparatus itself, such as the spring (No. 12, Plate 17)being broken or very weak, or some binding of the piston(8). The author has a very distinct recollection of onecase, in which such trouble was caused by a piece of scalefrom the casting lodging above the piston (8), just largeenough when it stood on edge to block the piston so lowthat the valve could not seat. Hard rapping on the valvecase would shake it down flat and stop the blow, but thenext emergency action would set it up again, causing itto stick as before. A careful examination on taking thevalve apart revealed the cause of the (78) Plate IS). Diseases of the Air Brake System. 79 If the brake sticks after emergency, but does not blowfrom the exhaust when the excess pressure is thrownagainst it, it is an indication that the main piston (No. 5,Plate 17) refuses to be forced back to normal may be from frost or dirt, but in the great majorityof cases will be found to be simply because the pressureput into the trainpipe is not yet high enough to overcomethat in the reser^oir. Bleeding the reservoir slightlyshould release it; but if it does not, then the blame mayfairly be laid on the valve. It must be taken apart,thoroughly cleaned, and then put together again. EMERGENCY ACTION WHEN NOT WANTED. This may result from a very weak graduating-spring(Plate 17, Xo. 22), or a failure of graduating-valve (7)to unseat properly, either because the pin which controlsit is broken, or else because it is surrounded with gumand dirt. It might also
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