A pneumatic brake actuator, comprising: a spring brake actuator comprising a spring chamber and a spring brake pressure chamber; a service brake actuator coupled with said spring brake actuator and comprising a service brake pressure chamber and a pushrod chamber; and a control valve operable to regulate fluid flow between said spring chamber and said service brake pressure chamber, said control valve comprising a seal moveable between an open position in which fluid can flow between said spring chamber and said service brake pressure chamber and a closed position in which fluid is blocked from flowing between said spring chamber and said service brake pressure chamber, wherein said seal comprises first and second surfaces, wherein said first surface is in fluid communication with said service brake pressure chamber, wherein said second surface is in fluid communication with a valve chamber that is not in fluid communication with said spring chamber or said service brake pressure chamber, and wherein said seal is arranged to move between said open position and said closed position based on a pressure in said service brake pressure chamber, wherein said control valve comprises a valve body with a channel formed therein for allowing fluid to flow between said spring chamber and said service brake pressure chamber when said seal is in its open position, wherein an interior surface of said valve body defines said channel, wherein said seal is positioned within said channel and blocks fluid from flowing through said channel when in its closed position, and wherein said valve chamber is enclosed by said seal and said valve body, characterized in that said seal comprises a first sealing surface that engages said valve body when said seal is in its closed position to block fluid from flowing through said channel, and second and third sealing surfaces (194, 198) each of which engages said valve body to seal said valve chamber from said spring chamber and said service brake pressure chamber, wherein said valve body comprises a transfer plate comprising upper and lower surfaces (146, 148) joined by a side wall, a cylindrical protrusion comprising upper and lower surfaces (152, 154) joined by a side wall, wherein said lower surface of said protrusion is joined to said upper surface of said transfer plate, and a retainer that is positioned within said channel to retain said seal within said channel. a spring brake actuator comprising a spring chamber and a spring brake pressure chamber; a service brake actuator coupled with said spring brake actuator and comprising a service brake pressure chamber and a pushrod chamber; and a control valve operable to regulate fluid flow between said spring chamber and said service brake pressure chamber, said control valve comprising a seal moveable between an open position in which fluid can flow between said spring chamber and said service brake pressure chamber and a closed position in which fluid is blocked from flowing between said spring chamber and said service brake pressure chamber, wherein said seal comprises first and second surfaces, wherein said first surface is in fluid communication with said service brake pressure chamber, wherein said second surface is in fluid communication with a valve chamber that is not in fluid communication with said spring chamber or said service brake pressure chamber, and wherein said seal is arranged to move between said open position and said closed position based on a pressure in said service brake pressure chamber, wherein said control valve comprises a valve body with a channel formed therein for allowing fluid to flow between said spring chamber and said service brake pressure chamber when said seal is in its open position, wherein an interior surface of said valve body defines said channel, wherein said seal is positioned within said channel and blocks fluid from flowing through said channel when in its closed position, and wherein said valve chamber is enclosed by said seal and said valve body, characterized in that said seal comprises a first sealing surface that engages said valve body when said seal is in its closed position to block fluid from flowing through said channel, and second and third sealing surfaces (194, 198) each of which engages said valve body to seal said valve chamber from said spring chamber and said service brake pressure chamber, wherein said valve body comprises a transfer plate comprising upper and lower surfaces (146, 148) joined by a side wall, a cylindrical protrusion comprising upper and lower surfaces (152, 154) joined by a side wall, wherein said lower surface of said protrusion is joined to said upper surface of said transfer plate, and a retainer that is positioned within said channel to retain said seal within said channel.