170 TRIPLE VALVES 



COMPARISON OF PLAIN AND QUICK-ACTION 

 TRIPLES 



Plain and quick-action triples work exactly the same in a 

 service application, but in emergency the quick-action triple 

 sets the brake quicker and gives a greater brake-cylinder 

 pressure. Also, the quick-action triple sets its brake harder 

 in emergency than it does in service application, owing to 

 the emergency valve, piston, and check- valve operating so 

 as to allow train-pipe pressure to enter the brake cylinder and 

 aid the auxiliary pressure in applying the brake. The plain 

 triple sets its brake quicker in emergency than it does in ser- 

 vice, owing to the use of larger ports; but the brake does not 

 set any harder, because it simply has auxiliary pressure to 

 use in applying the brakes in either service or emergency. 



When a quick-action triple goes into emergency position, a 

 sudden brake-pipe reduction is made near it when the emer- 

 gency valve opens. This sudden reduction starts the next 

 quick-action triple, and that starts the next, and so on through- 

 out the train. If from any defect one triple goes into quick 

 action, all will follow. 



Ordinarily, a gradual brake-pipe reduction of about 20 Ib. 

 will cause a plain or a quick-action triple valve to equalize 

 the pressures between the auxiliary and brake cylinders at 

 about 50 Ib. In emergency, with a quick-action triple, the 

 pressures are equalized at about 60 Ib., while with a plain 

 triple, the same pressure is obtained in the cylinder in emer- 

 gency as in a full-service application, namely, 50 Ib. With 

 quick-action triples, a sudden brake-pipe reduction of 10 or 12 Ib. 

 will produce a full emergency action of the brakes; while, 

 with a plain triple, a reduction of about 20 Ib. is necessary. 

 The reason for this is that a 12-lb. reduction will cause the 

 emergency valves of the first triples to open and produce a 

 further brake-pipe reduction. Brake-pipe pressure is not 

 affected in this way when a plain triple goes into emergency, 

 and, therefore, while a sudden 12 Ib. reduction would force the 

 triple to emergency position, it would not stay there, as it 

 would be forced back to lap or perhaps to release, as soon as 

 auxiliary pressure had reduced the 12 Ib. It is necessary, 

 therefore, to reduce brake-pipe pressure below that at which 



