Adding an Air Compressor (1 Viewer)

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Peter A Forbes

Free Member
Nov 23, 2014
270
184
Rushden, Northants, UK
Funster No
34,314
MH
Mercedes 614D
Exp
10+
For reasons best known to themselves, or probably because the Mercedes Vario has disc brakes front and rear, Mercedes fitted spring brakes for the handbrake on both the 614 and 814 models.

The higher capacity 814 has air brakes all round and an engine-driven compressor.

The 614 has vacuum brakes but still has the spring brakes for parking, but as the vacuum pump takes up the space where the compressor would go, they fitted a very twee little 24V compressor sourced from Knorr-Bremse or Bosch.

The only problem is, that if the compressor fails, you are stuck, big time.

The electric compressor is activated by the alternator warning light feed so it only has power when the engine is running, and there are pressure switches to shut it off if the tanks are full.

So, the choices are:

Fit an additional pressure source to work in parallel with the existing one, or fit the air compressor from the 814D and arrange an external vacuum pump for the main brakes.

Of the two, fitting another compressor is the simplest and doesn't affect anything if it fails, but sourcing something suitable is not easy, other than the original which is the wrong side of £1k.

Ideas would be appreciated, but they must be practical/possible and must be within a budget of £150 max.

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Peter
 
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DP+JAY

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Mar 17, 2010
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Dalbeattie
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Laika 5009
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since 2007, 25 years tuggin before that.
Some idea if the compressor output would be useful?
Would some thing like a ring RAC900 work? or maybe a small mains unit & inverter.
 
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Peter A Forbes

Peter A Forbes

Free Member
Nov 23, 2014
270
184
Rushden, Northants, UK
Funster No
34,314
MH
Mercedes 614D
Exp
10+
I can't find a spec at present, but it will have to be rated for continuous operation at least.

I had thought about a mains powered unit through a compressor, might be the way to go.

Thanks,

Peter
 
Aug 18, 2014
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136,789
Lorca,Murcia,Spain
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32,898
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Transit PVC
Exp
16 years since restarting
In reality you only want something to cover the possibility if the original fails ? If so I'd go down the route of small compact mains or battery one, as suggested.
 

DP+JAY

LIFE MEMBER
Mar 17, 2010
2,542
14,801
Dalbeattie
Funster No
10,674
MH
Laika 5009
Exp
since 2007, 25 years tuggin before that.
I can't find a spec at present, but it will have to be rated for continuous operation at least.

I had thought about a mains powered unit through a compressor, might be the way to go.

Thanks,

Peter
Why woul it be in continuous use?
Surely it only needs too build up enough air to operate the brake as & when it's used?
From what I can see it is controlled by the pressure switch & only runs as & when the pressure drops.

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Peter A Forbes

Peter A Forbes

Free Member
Nov 23, 2014
270
184
Rushden, Northants, UK
Funster No
34,314
MH
Mercedes 614D
Exp
10+
Yes, but if it has to run it will run for fairly long periods at pretty high pressure, I',m not sure that the small mini-compressors are up to it.

We already have a decent compressor, we can buy a twin cylinder version of that one:

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Peter
 

Trikeman

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Aug 22, 2012
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Wilds of Ceredigion.
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AT 634 Apache.
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Since 2011.
Hi Peter,
just be a little careful here, you are 'working on' a type approved brake system. Making any changes 'could' result in headaches (prohibition) should it be stopped by DVSA (old VOSA) and I dread to think what could happen in the event (god forbid) of an RTA.

Just a small pearl of wisdom.(y)

Regards,

Trikeman.;)
 
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Peter A Forbes

Peter A Forbes

Free Member
Nov 23, 2014
270
184
Rushden, Northants, UK
Funster No
34,314
MH
Mercedes 614D
Exp
10+
Thanks for that, I'll be adding a feature to enable an external air source to release the handbrake, quite common on trucks, so there shouldn't be any issue.

Service brakes I'd have a think about it first :)

I used to fit 3rd line air systems to new Scania units back in the 1970's, all done without any real drawings, but they always worked as they should. They came over with 2-line brakes if they were LHD.

Peter
 

Sel

Free Member
Apr 3, 2017
4
0
Warrington
Funster No
48,014
MH
A class
Exp
Since 2013
Hi I have a 612d vario fitted with the air handbrake, I can't build up enough pressure to release the break, I can't find the connection point for fitting a comppresser hose, I know there should be one for towing in the event of a breakdown. Cheers sel
 

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