Exhaust break

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bromleyxphil
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Exhaust break

Postby bromleyxphil » Thu Feb 01, 2018 1:19 pm

Hi next job is to fit an exhaust break to the truck. I have spoken to MAN and they have specified an exhaust butterfly valve unit that completely closes off the exhaust. I had in my brain “don’t know where this information came from” that the valve should have a hole in it or at least not close completely. Anyone know anything about these units? Does the “back pressure not just build and build if it has no where to go? The unit is closed by an air cylinder so maybe that is set to a maximum pressure? I will try to post a diagram of the unit but I seem to have issues posting pictures on here.

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Re: Exhaust break

Postby bromleyxphil » Thu Feb 01, 2018 1:35 pm

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Re: Exhaust break

Postby bromleyxphil » Thu Feb 01, 2018 1:37 pm

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Re: Exhaust break

Postby bromleyxphil » Thu Feb 01, 2018 1:38 pm

This is one fitted to another truck.
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Ivan C
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Re: Exhaust break

Postby Ivan C » Thu Feb 01, 2018 2:57 pm

A hole would defeat the purpose, the pressure would rise dramatically because of the reduction in area. Perhaps you have an EGR valve blanking plate in mind? These often have a bleed hole.
What is happening is that the engine is being used as a compesser, driven by the road wheels, rather the other way round.
I'd imagine there would be enough leakage round the flap and back through the inlet to avoid excess pressure.
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Zoltan
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Re: Exhaust break

Postby Zoltan » Sat Feb 03, 2018 6:16 am

I understand that stronger exhaust valve springs need to be fitted if an exhaust brake is fitted to a Cummins, same science would apply to an MAN. May be worth asking that question

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Re: Exhaust break

Postby NeilandPat » Sat Feb 03, 2018 9:48 pm

I have this brake on our Mercedes.

It definitely doesn't close completely and has an adjustable stopper to prevent total closure.

My thinking that total closure of the valve would cause an overload of back pressure , hence leaving a small gap to limit the pressure.

I would think that total closure would firstly blow all the oil seals in the engine and out of all the breathers as the the pressure inside the engine casing would be too high.

I have heard of folks having lots of oil leaks after long down hills

I have heard of people drilling a small hole in the flap but I would think that a kit from MAN would be good to go with the right clearance pre set. I can't imagine it would need adaption.

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Re: Exhaust break

Postby Ivan C » Sun Feb 04, 2018 9:34 am

Two very valid points.
Looking closer at the set-up on my truck there is a fixed stop to limit travel of the flap, the length of the rod on the air cylinder is also adjustable.
I'd check valve spring specs between the two engines.
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Re: Exhaust break

Postby NeilandPat » Sun Feb 04, 2018 11:59 am

I think the setup of these retarders is crucial.

If you get it wrong its either not going to work well or its going to over stress the engine.

Once set ot shouldnt need adjustment ot maintanance

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Re: Exhaust break

Postby bromleyxphil » Sun Feb 04, 2018 7:44 pm

Well chaps if I wasn’t worried before I am now. Ivan if I am right the stop on the arm is on the opening side. I am going to have to try to find out some more info but it’s a bit sparse. I will see if I can get any more joy from MAN.


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