A control valve includes a diaphragm with a flow path with a predetermined cross-section from a brake pipe to a first side of the diaphragm and another flow path having another predetermined cross-section from a second side of the diaphragm to atmosphere. A dump valve prevents flow from the brake pipe to atmosphere. A method for operating a control valve includes supplying brake pipe air to a first side of a diaphragm through a flow path having a predetermined cross-section and permitting or preventing reference air flow to atmosphere through another flow path having another predetermined cross-section. The method further includes supplying reference air to a dump valve that prevents brake pipe air flow to atmosphere.