THE QUICK-ACTION DISTRIBUTING VALVE. NO. 6 DISTRIBUTING VALVE WITH QUICK-ACTION With the advent of all-air-braked trains it became necessary to supply additional functions to the plain triple-valves referred to earlier in this work; no changes were found necessary in its action in response to service reductions, but at emergency applications on long, air-braked trains, the forward brakes would apply with full force before the brakes on the rear cars had started to set, resulting in the sudden "bunching" of trains with disastrous effects; in other words, the slack between the cars would close-in more rapidly than the brakes could serially apply throughout the train from front to rear. Then the quick-action triple valve was evolved for freight and passenger cars, in the service action of which there was no difference from that of the plain triplevalve; but, following a quick, heavy reduction, the new triple was devised to discharge a portion of the brake-pipe air, and further-to make this discharge into the brake cylinder, before the latter could receive any appreciable amount of auxiliary-reservoir pressure, resulting in an increased braking pressure at emergency as well as securing the full-on application of the rearward brakes before the slack could run in. It has been found desirable in recent years to apply quick-action triple-valves to locomotive tenders, and this is particularly necessary when in case of doubleheading, the engineer of the leading locomotive operates the brakes, as, if both engines and tenders are equipped with plain triple valves it is quite commonly impossible for him to secure quick action of the train brakes, owing to the large volume of brake-pipe air to be reduced between his brake-valve and the quick-action triple on the first car, and the resistance to air flow due to the several short bends and possible elbows in the brake pipe of both locomotives. As the E-T locomotive brake depends upon the distributing valve for the regulation of brake-cylinder pressure, and the graduating portion of the ordinary distributing valve acts on the same principle as the plain triple-valve, it follows that it is just as necessary that the distributing valve should possess the same quick-action feature of brake-pipe air-vent at emergency applications; on the theory, however, that some railroads do not encourage the double-heading of trains, the Westinghouse Air Brake Company furnish the distributing valve of the latest improved E-T equipment, No. 6 type, without the quick-action device, unless such shall be specified when ordering. |