Stabilized brake control valve

A brake control valve for operating a vehicle's air brakes in response to brake pipe pressure in a brake pipe, the brake control valve comprising:

• a housing including a quick braking chamber;
• a piston in the housing and subject to brake pipe pressure on one side of the piston;
• a bore in the housing connecting the quick braking chamber via a first port at a first end and the one side of the piston at a second end;
• the bore having a first bore portion of a first diameter and a second portion of a second diameter larger than the first diameter, the first bore portion connecting the one side of the piston to the second bore portion;
• a first operator in the bore connected to the piston;
• a seal on the first operator dimensioned to form a seal with the first bore portion and not with the second bore portion;
• and
• the seal is located on the operator to lie in the first bore portion for a first segment of a range of piston positions and to lie in the second bore portion for a second segment of the range of piston positions.