Deadman brake valve isolation cock. Should always be in the open position. Can be in the closed position if there is a fault or as part of a proceedure.
The deadman is a part of the combined traction brake controller (CTBC), and will vent the trainline air (thus applying the brakes) if the CTBC is realeased, for example, by a collasped driver, in any position other than rheo1 & hold.
