Fixed Orifice Exhaust Brakes
A fixed orifice exhaust brake is the most cost effective supplemental braking solution. The term “fixed orifice” refers to a hole in the butterfly valve, which allows a set amount of exhaust bypass at a pre-determined engine speed. A fixed orifice exhaust brake does not have any pressure regulation mechanism, which makes it an economical choice over a higher performance, pressure regulating exhaust brake, such as the PRXB.
A fixed orifice exhaust brake is calibrated to generate its maximum backpressure at a specific engine speed. This engine speed is usually the maximum engine operating speed. As a result of the fixed butterfly orifice being sized for high RPM and exhaust flow, lower engine speed brake performance suffers, due to lower than optimal exhaust backpressure.
Fixed orifice brakes will provide repeatable backpressures at their pre-calibrated engine RPM, however they do not offer any over-speed protection nor optimize braking power throughout the entire RPM range. Exhaust backpressure can potentially exceed the engine’s maximum allowable backpressure if the engine operating speed ever exceeds the engine speed that the fixed orifice exhaust brake was calibrated for. Pacbrake offers a higher performance pressure regulated exhaust brake called the PRXB, if overspeed protection and constant exhaust backpressure are requirements.