Abstract: A tank car bottom unloading valve that meets A.A.R. specifications which can be dually-operated either from above or below the tank, wherein the valve is retained in a heavy, longitudinally sloped mounting flange by a segmented ring which does not interfere with the valve actuating mechanism and yet allows the containment of the valve up inside the tank so as not to result in hazardous protrusion of the body of the valve from the bottom of the tank. Said vale is shut from below by an over-center cam and link mechanism which locks the valve poppet on its seat through a resilient compression spring but which does not lock-up the valve when it is shut from above, so that lower working torque is required by the operator and less maximum stress is imposed on the valve in its operation, and there is less criticality of adjustment upon assembly. A valve actuating lever disengages from the over-center cam and link mechanism for rotation and hookup in an out-of-the-way place below the tank car.

Abstract: A manifold mounting pairs of relief valves in side-by-side clusters having a slide-rod interlock cooperating with swing-mounted clapper discs and operationally engaging handles connected thereto for selectively isolating one valve at a time from pressure in the manifold in preparation for its removal and replacement under pressure therefrom.