Foot Brake Module with a Guiding Feature on a Relay Piston

A valve assembly is provided comprising: an air supply port; an air delivery port; a guide sleeve; and a piston positioned in the guide sleeve and movable between first and second positions to allow air to flow from the air supply port to the air delivery port, wherein a gap is defined between a minor outer diameter of a shaft of the piston and the guide sleeve; wherein the shaft defines an inner bore for passage of air and comprises a plurality of raised surfaces around a circumference of the shaft that narrows the gap and thereby reduces tilting of the piston as it moves in the guide sleeve between the first and second positions. Other embodiments are provided.