triple valve

plural triple valves

1. rail transportIn railway air braking systems, a valve that performs three functions.

   By 1873, the triple valve had been developed satisfactorily in a form which it retained for many years, and by it the automatic character of the brake was ensured. The valve got its name from its triple function of applying the brakes, releasing them, and re-charging the auxiliary reservoirs.

   1946 November and December, “George Westinghouse, 1846-1914”, in Railway Magazine, pages 374–375

   1 more example

   The basic equipment on each vehicle consists of the auxiliary reservoir, the triple valve and the brake cylinders. When the train pipe pressure is reduced, the triple valve spills air out of the auxiliary reservoir until its pressure becomes equal to that of the train pipe; this air is passed into the brake cylinders.

   1964 March, “Train braking - the next steps”, in Modern Railways, page 186