Fixed Orifice Exhaust Brake Operation
The exhaust brake was introduced into the market place over 50 years ago as the need for supplemental braking was requested. The exhaust brake works on a principle of restricting the exhaust flow on the exhaust stroke of the engine to provide retarding. The amount of exhaust restriction allowed is based on the strength of the exhaust valve springs as not to allow valve float throughout the normal engine cycle. The conventional design to achieve the correct amount of backpressure is with a fixed orifice hole in a butterfly valve, sized to limit backpressure to a specific amount at governed engine RPM.
Although fixed orifice exhaust brake designs do work well, the engine must be held near governed engine RPM to optimize their effectiveness. With this challenge in mind, Pacbrake engineers invented the patented PRXB, which holds the maximum allowable backpressure throughout the entire RPM range.