There are two types of diesel engine brakes.
1. The Compression Release brake is a set of valves, one in each cylinder, that opens when the engine is at or near the top of the compression stroke to release the compressed air to atmosphere, causing a vacuum to develop during the unpowered power stroke. This vacuum causes the engine braking effect, and a tremendous amount of noise. This setup is commonly called a Jake Brake or an engine brake.
2. An Exhaust brake is a means of slowing a diesel engine by closing off the exhaust path from the engine, causing the exhaust gases to be compressed in the exhaust manifold, and in the cylinder. Since the exhaust is being compressed, and there is no fuel being applied, the engine works backwards, slowing down the vehicle.
Pacbrake is a manufacturer of emission valves
, engine brakes
and exhaust brakes
serving the diesel engine industry. It is not a type of brake, as they make both and more. Jacobs Vehicle Systems, maker of the original Jake Brake, also makes exhaust brakes, and more.