D-Celerator Exhaust Brake
I was working on our exhaust brake this week (installing a new air cylinder), and thought I might take the opportunity to post a few photos and a little info. It is a U. S. Gear Super Duty D-Celerator, Model EXB-4000M, air-activated, for 4" exhaust pipe. This brake was installed on our coach when we bought it. I knew nothing about these devices before we bought our coach, but I have of necessity learned a bit along the way. I can't compare this exhaust brake to others on the market, because this is the only one I have ever used. It does seem to provide a worthwhile braking force when traveling in the mountains, but of course it is nowhere near as effective as the Allison transmission retarder. Still, for those members who, like us, do not have a retarder it is one possible means to improve braking performance on long down grades.
The principle of these brakes is pretty simple - you close a big full-bore valve inside the exhaust pipe (downstream of turbo), and the increased engine back pressure, transmitted through the transmission to the rear wheels, slows the vehicle. Exhaust brakes work better at higher engine RPM, so you need to manage your gear selection to take maximum advantage. If the torque converter in your transmission does not lock up in the higher gears, the effectiveness of the exhaust brake is severely reduced. The back pressure produced by the brake must be controlled, because excessive back pressure can cause "valve float" and damage the engine. All of the exhaust brakes currently on the market utilize some means of limiting the back pressure.
Our exhaust brake is designed to produce a maximum of 35 psi of back pressure, because our Cummins C8.3 has the standard exhaust valve springs. If desired, I could install heavy duty "60 pound" valve springs in our engine, which would then allow us to increase the back pressure produced by our brake to 54 psi. 60 psi seems to be the generally accepted (by manufacturers) max allowed pressure for exhaust brakes.
I won't go into any detail about how different manufacturers control back pressure - they all have their own pet design. The brake on our coach has a small spring loaded "bypass" valve that allows exhaust flow around the large closed main valve when maximum back pressure is achieved. You can see this bypass port in one of the photos. The idea is that when the brake is activated, back pressure will rise to the maximum value, then be held there. This variable pressure design allows better performance at lower engine speeds, while at the same time protecting the valve train at high engine speeds.
By writing this little report, I'm not trying to promote this product. I just want to add a few bits of info to the great collection of knowledge on this Forum, and perhaps enlighten those who, like me, have never seen the inside of a exhaust brake. If anyone has any questions about this model, I'll be happy to try to answer.
More reading material here:
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Topic: D-Celerator Exhaust Brake