Exhaust Brakes

[Viscount]

I noted from an earlier post the suggestion that exhaust brakes were to stop an engine flood in the event of rapid deceleration. I had mine refitted on the understanding that they stopped smoke / fumes being emitted whilst starting and on tickover. Perhaps it is both?

Anyway, mine have stopped working properly (2 x Volvo AD31) isofar as they switch in and out when the throttle is operated whilst the ignition is on and engines off but stay open when engines running which kind of defeats the purpose. Closer examination reveals that they operate on the behest of a microswitch which changes state when the throttle is operated - this in turn operates a relay which puts 12V on what I take to be a control wire going to the exhaust brake solenoid (this unit also has permanent +12v and -12v directly from the starter motor). The wiring diagram for the engine only shows 2 wires going to the solenoid - a -12v and the control wire from the relay - it seems therefore that what I have is either wrong or more up to date than the original equipment. Any advice / experience welcome.

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[studgies]

Ours are discinected so I am no help sorry!

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[adarcy]

Re: I\'m confused

An exhaust brake on a lorry shuts off the exhaust flow so that the engine act as a great compressor and slows the truck without using the friction brakes.

An anti-syphoning exhaust flap may well stop and engine drowning on rapid deceleration if the water is able to back up the exhaust system and may hydraulic the engine.

I really don't see how either of these have anything to do with smoke fumes on starting. If you block partly or completely the exhaust outlet, how is the engine going to start?

From what you describe, it seems like a sytem whereby switching off the ignition will shut down the diesel even if it is in a "runaway" condition. Sounds v useful sounds as if it is working fine although I have no experience of AD31s - others here have and may well chip in

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by adarcy on 31/08/2004 17:05 (server time).</FONT></P>

 

[PaulF]

We found these things fitted to our AQAD41A's and was told their original purpose is for smoke reduction on start up . The partial closure of the exhaust puts a load on the engine, this does reduce smoke levels. The same thing is achieved by dropping the engines into gear immediately on start up. If you do it on tickover with one engine ahead and one astern, this will reduce warp tension in a marina if one was worried about it, but at tickover speeds the tension is not that high anyway. I would expect the flaps to shut when the Key ignition(wrong word for a diesel anyway but hey, we are used to it now) is turned on and the flap should stay shut until the throttle is opened, this should be as it is put in gear then the requirement goes away as 'in gear' is the load. One of our solenoids packed up so we just use the above means to load the motors. It works , so why not?

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[Viscount]

Thanks for feedback. Further checking shows that they are quite effective in reducing smoke on startup as I disconnected the mechanical linkage from the solenoid and operated manually - the difference in emissions is noticeable. My "problem" seems to be that the solenoid itself now has a timer in it such that if the throttle is operated and released within about 5 seconds, the exhaust brake releases but does not come back on when on tickover. If the throttle is operated for more than about 5 seconds then the exhaust brake kicks back in. What I had been doing was starting the engines and flicking the throttle to get the electrics to show a stable position - i.e. get the battery lights out and the rev counters working. If I start them and let them just tickover, it seems to be OK.

Studgies - what amount of smoke do you get on cold start? Ours is white and a bit offputting (without exhaust braking) particularly with the cover open at the back.

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