clack valve

— The connecting pipe between a locomotive injector and the boiler, through which the water is forced into the boiler against the steam pressure within, is provided with a "clack-valve," which allows the water to pass in the inward direction only and not the outward; this is housed in a "clack-box". No question of "advantages or disadvantages" attaches to the use of a clack-box; it is a necessary part of locomotive equipment.