The PRXB (pressure regulated exhaust brake) from Pacbrake is its flagship product, which provides performance, safety and savings. The PRXB delivers constant exhaust pressure (braking) as early as 1200 rpm all the way to maximum rpm. It provides safety by increasing vehicle stability and reducing the amount of brake fade. Controlled by a master ON/OFF switch, the exhaust brake provides whisper quiet supplemental braking that allows service brakes to be used much less, ultimately paying for itself with fewer brake jobs. With the ability to be left on all the time, it is ideal for city driving or steep, downhill grades. Pacbrake: (800) 663-0096, Online Information.