This SAE Recommended Practice establishes minimum tolerance requirements for pilot operated and mechanically actuated modulating type valves, and through type valves used in the service brake control system when tested in accordance with the test procedure outlined in SAE J1859. This document applies to the nominal input-output characteristics as specified by vehicle original equipment manufacturer and labeled by the valve manufacturer as outlined in SAE J1860. The tolerance requirements will include:

Crack (opening) pressure or force. Crack pressure may be measured at the initial output pressure or as the pressure differential before output pressure exceeds 14 kPa (2 psi). Crack force may be measured at initial output pressure or before output pressure exceeds 14 kPa (2 psi).
Pressure differential (input-output)