Auxiliary compressor for charging air system

[Jeremy]

I've read various posts in the past about people fitting an electrical compressor to their buses in order to charge up their air systems before starting the engine, in order to avoid excessive early-morning idling when leaving campsites etc. Can anyone direct me to photos showing such a compressor, or perhaps provide a link to a website somewhere with a suitable compressor model for sale?

The reason for this is that I'm trying to get an idea of the size of compressor usually used for this task. Whilst fiddling with my old Cadillac today ('84 Coupe De Ville), I realised that it has a very nice 12v compressor on it that runs the self leveling suspension system; it's a neat little unit, very smooth and quiet, and I'd be interested to know whether it could be used on the bus. I've no idea what the specs are, but I connected it to a pressure gauge and got a reading of 100psi very quickly, with the motor barely seeming to notice the load. It would undoubtedly have gone a lot higher, but I didn't dare test the temporary connections I had made. I'm sure the CFM is low, but that probably doesn't matter much in this application.

Anyone got any thoughts on this idea? What kind of air pressure do the brakes typically need to release? Note that my bus doesn't have air suspension, but it does have an air-operated door - this can be closed manually without an air supply, but it would be very handy to be able to continue to close it remotely even when parked up for a few days.

Jeremy

[MattC]

Jeremy,

No intention to hijack yer post.  I was thinking about installing a compressor for the same reason(s) you posted. 

After searching for a couple hours in posts and google, the only quiet compressor of any size I could find was: 

            http://www.generatordepot.us/index.asp?PageAction=VIEWPROD&ProdID=107

However I'm sure my MCI wouldn't choke having a Caddy part or two stowed away somewhere.  Very interested in how your solution plays out. 

Thanks!

[johns4104s]

The extra compressor is also helpful if you are being towed and the tow truck does not have rear air lines.

John

[buswarrior]

You want an auxiliary compressor that runs in oil.

Better performance due to closer tolerances, the oil lubes and cools it.
Oil-less have to be made looser to accommodate the swell from heat.

Oil-less will get awfully hot before it is done airing up a coach.

Don't be fooled by horsepower or top pressure or tank size.

It is cfm's at 90 lbs that you're looking for.
Get the most you can get for the money you want to spend.

happy coaching!
buswarrior

[Jeremy]

I found a photo on Ebay of the same part I have:



I also see that there are very similar compressors available for lots of different cars - I guess air suspension is quite common nowdays. Typically they don't seem particularly expensive either - if car air suspension compressors are up to the job of pumping up a bus's tanks then this might be a good solution for other people.

Anyone else got any thoughts on their suitability? The only concern for me might be the low flow rate - but as long as you don't have any air leaks this would just mean the compressor would run for longer to charge the system up. In many ways I would rather use a proper, rugged, designed-for-vehicle-use original-equipment item than some Harbour-Freight type thing with shiny red paint and great specs, but made-in-China and only designed for occasional use with a very low duty cycle

Jeremy

Added after simultaneous post: I'm sure the point about an oil-cooled compressor is well made. I will try running my Caddy compressor under load for 30 minutes or so to see how it handles it

[Hartley]

The typical compressor rating should be around 3.5 to 6.5 cu.ft/min @90 psi.
It takes that much to get the air ride suspension tanks to wake up providing you don't have any air leaks.

I have a Dewalt that goes to 150 psi @ 3.5 cu.ft/min and it strains to get enough air built up so the accessory tanks start filling. I guess a few leaks may be the reason for that. However I have used the same compressor to fully air up and operate another bus to move it and although it gets a bit hot it still works.

I think I read that the OEM bus compressors are 10 to 15 Cu.ft/min @ 120 psi
and most buses need every bit of air they can get just to stay drivable.

Show me a bus that doesn't leak and I will start pointing at the owner that either has OCD or way too much time on his hands. Heck by the time I would get the air leaks stopped, something else would be broken and leaking...

Stuff Leaks ....

Dave....

[Lin]

I have an older version of this one.  It airs the bus up in about ten minutes.  It's also easy to grab and move for other tasks.  It may not be silent, but it works great for a relatively peaceful, non-toxic start at campgrounds.  I think I paid about $60. for it used.  Try Craigslist.

[johns4104s]

Lin,

Which one?

John

[Lin]

Sorry, I must have left the link off!

http://doitbest.com/main.aspx?memberid=1875h&associate=true&pageid=64&sku=364134

[Sean]

Jeremy,

Our Neoplan uses a lot of air.  That's because we have an air-operated entry door, an air-flush toilet, and air suspension, which "uses" air constantly as weight shifts around the bus and the ride-height valves exhaust or add air to compensate.

We've been through three different compressors before finding one that does the job.  It's a Hitachi 4-gallon contractor-type, oiled, which puts out 4.0 CFM at 100 PSI (it's a 135-PSI compressor).  It has a 1.6 HP motor to achieve this.  In our application, where we have set the output regulator at about 85 PSI, it runs every half hour or so for about 20 seconds.

Previously, we burned up two oil-free 150-PSI Porter Cable units, and before that we had a little Senco nailer job that seemed to run endlessly trying to keep up.

Since the compressor is on all the time, we never have to "air up" the bus, and the brakes are always ready to go.  That said, if we let the bus air down all the way, that compressor would likely take twenty minutes to air it up -- there's a lot of big tanks on this bus, and they all have to come up to pressure for everything to work (two brake tanks, an emergency brake tank, auxilliary tank, main tank, and a separate tank for the suspension, not to mention filling all six air bags).

Emergency brakes will not release until you have 60 PSI in the system.  120 PSI is typical governor cut-out on a bus, with 90 PSI being cut-in.

Frankly, I don't think a little 12-volt automotive compressor will do the job, and you are likely to just burn it out trying.

HTH,

-Sean
http://ourodyssey.blogspot.com

[Jeremy]

Thanks for the replies and for the 'numbers' to be aiming at with a compressor. I will do some tests with my Caddy compressor, but will set my expectations low. It might be it has a better chance with my bus due to the lack of an air suspension system to cope with. Alternatively I suppose I could isolate the air-powered door somehow, which is the thing I would really like to able to continue to operate when camping. Or I could simply plumb the Caddy compressor in now, but in such a way that it could easily be replaced by something better if and when it fails.

Thanks

Jeremy

[johns4104s]

Sean,

Were did you buy the Hitatchi and what did you pay?

Thanks

John

[bevans6]

I was playing around with this on the weekend.  I used my little oil-less direct drive  compressor to air up the bus, it did it fine but took 10 to 15 minutes.  the compressor got a little warm, to be sure.  I left it connected for a couple of hours, it never cycled back on, but my bus takes about 5 hours to drop from around 100 psi to 60 psi.  I connected it to a schrader valve on the air muffler in the engine bay with a latch-on tire filling chuck.
I think the longer term plan will be to get or make up a small 120 volt motor/belt driven compressor head, run it at low speed from about a 1 hp motor, and mount it in the engine bay around where the a/c compressor is now.  I don't think there is a need for a tank, since it would be connected to the bus tanks when in use.  Probably have a ball-valve to isolate it when not in use.

Brian

[BG6]

I'm not willing to use up my starter battery on 10 minutes of running a compressor.  The day may come that I have battery issues and only one chance to get started . . .and not know it . . .

A better idea is to use a 120V compressor running from the inverter -- light off the engine, and then hit the compressor for a high-speed air-up.  By the time the engine is warmed up enough to move, you're aired up.  If you're on shore power, then you can air up before you light.

[buswarrior]

mythbusters!

Save some fuel!  That's a big reason for the aux air compressor!

A busnut has no need to "warm up" the engine to move from a camping spot. It just smogs out the neighbours, wastes fuel and makes a lot of noise.

If the engine is running and the oil pressure is up, which happens in 5 seconds or so, you are good to roll away from a campsite.

Nobody but a few of us are running in winter conditions, where a small bit of consideration must be paid, but the engine was pre-heated to start and good to go anyway.

Yes, some grizzled old veteran of the road will tell you all about how he blew a motor back in '49 doing whatever...he has idled on start-up for 10 minutes every day since with no troubles....truth be told, it was looking for a time to blow up and he's spent fuel money every day unnecessarily.

I'm talking moving out of the campground, not starting off on the side of a mountain for the big climb under full power.
It'll warm up quite nicely making your moves out to the road, giving you something for that expensive fuel.

Just don't jump hard or deep on the throttle until you see some movement in the temp gauge.

The world is looking for people to punish with more restrictions, let's not get them pissed at busnuts.

happy coaching!
buswarrior