Adding an Air Compressor

[Peter A Forbes]

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.

Broken Link Removed

Broken Link Removed

Peter

 

[DP+JAY]

Some idea if the compressor output would be useful?
Would some thing like a ring RAC900 work? or maybe a small mains unit & inverter.

 

[Peter A Forbes]

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

 

[gus-lopez]

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]

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.

^{_{Subscribers  do not see these advertisements}}

 

[Peter A Forbes]

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:

Broken Link Removed

Peter

 

[Trikeman]

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.

Regards,

Trikeman.

 

[Peter A Forbes]

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]

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

 

[tonyidle]

Use an alternator with vacuum pump built on to it for the service brakes then fit the 814 compressor where it should be. A few alternators to choose from here:

http://www.ebay.co.uk/sch/i.html?_f...uum.TRS0&_nkw=alternator+with+vacuum&_sacat=0

^{_{Subscribers  do not see these advertisements}}