Foot brake module with a guiding feature on a relay piston

A valve assembly comprising:

• primary and secondary supply ports;
• primary and secondary delivery ports;
• a guide sleeve;
• a first piston configured to move in response to actuation of a brake pedal, wherein movement of the first piston causes air to flow from the primary supply port to the primary delivery port and to cause air to accumulate in a chamber of the foot brake assembly;
• a second piston configured to move within the guide sleeve in response to an accumulation of air in the chamber, wherein movement of the second piston causes air to flow from the secondary supply port to the secondary delivery port;
• and
• a set of guiding features positioned on the second piston to reduce tilting of the second piston in the guide sleeve.

A valve assembly comprising:

• a guide sleeve;
• a relay piston positioned in the guide sleeve;
• and
• means for reducing tilting of the relay piston as it moves in the guide sleeve, wherein the means for reducing tilting comprises a plurality of raised surfaces along a circumference of a shaft of the relay piston.