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 is calibrated to generate its maximum back pressure 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 back pressure.
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.
Fixed orifice brakes will provide repeatable back pressures 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 back pressure 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.
A PRXB is a Pressure Regulated Exhaust Brake that offers the highest retarding power for the lowest price available. Although the PRXB’s retarding power is comparable to that of a compression release engine brake, the manufacturing and installation costs are significantly less.
Conventional exhaust brakes experience a reduced exhaust back pressure at low engine speeds, resulting in an unnecessary loss of braking power. Pacbrake’s innovative PRXB addresses this issue with a patented waste gate design that regulates exhaust back pressure as engine speed changes. The valve maintains near constant engine back pressure throughout the entire RPM range, providing maximum exhaust braking power at all times.
Controlled by a master ON/OFF switch, Pacbrake’s exhaust brakes provide whisper quiet supplemental braking that allows service brakes to be used much less, ultimately saving money. They have the ability to be left on all the time, making it ideal for in-city driving or for steep, downhill grades. This product pays for itself as less wear on the brake pads means fewer brake jobs.
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