Abstract: A control valve having, in a series with a first inlet valve of a quick brake volume, two different rates of flow restrictions operable as a function of the position of the piston. The first flow rate of one first restriction is insufficient to cause the piston to a braking position for applying a minimum service application for first range of piston positions which would generally be produced by the mechanical vibration. The second restriction has a greater flow and will accelerate the piston to a braking position for a second range of piston positions which will be produced by the reduction of the brake pipe pressure on one face of the piston. By providing two flow rates, the valve becomes insensitive to mechanically produced forces while maintaining the reaction time of the valve to fluidically produced reduction of brake pipe pressure.