Recommendation on sizing external air compressor

TomC · August 13, 2017, 07:19:37 AM

The surprising thing that keeps the California compressor quiet, is having the small 6" long tubes coming off the air cleaners. That really quiets the intake. I don't know of a quieter compressor-except maybe one made from an old refrigerator compressor. Good Luck, TomC

Iceni John · August 13, 2017, 10:41:25 AM

I have a Harbor Fright twin-tank 2HP compressor that's mounted between the frame rails above the front axle (one of the last free spaces under the bus that I can find for it!), and it's fine for occasional use. It can air the entire bus in about fifteen minutes or so, but I usually have it connected only to the accessories system and its three air outlets around the bus. There's a simple self-draining air filter that takes out a surprising amount of moisture from the air before it reaches the accessories tank, and I also installed a valve and air line into the wet tank for airing the entire bus in an emergency. After my debacle earlier this year that required a tow truck, I've put an air inlet fitting on the end of the compressor's drain line next to the front door, making it easy for a tow truck to connect its air to the bus.

The compressor is fairly noisy, but maybe I can quieten it slightly by using 40-weight CF-2 oil in it?! At least it doesn't need a slobber tube.

John

windtrader · August 13, 2017, 10:46:04 AM

Update. going to rethink what I need for aux air. I've got an older compressor I can stuff in a bay for awhile. Oil unit, nice and quiet. Great conversation and sharing. made me take a pause to do it right for what I need.

bevans6 · August 13, 2017, 11:28:00 AM

What I'm going to do when I get around to it is put an old heavy duty Webster two cylinder compressor head and 1 hp motor in a bay, plumb it to the ping tank so it feeds through the air dryer, control it so it doesn't exceed the governor air pressure, and run the head slow so it's nice and quiet. No tank except the bus tanks. I once set up my little pancake compressor to air up the bus, it went over the governor cut-out and I found it just noisily dumping air on the ground.

windtrader · August 13, 2017, 01:27:53 PM

The reason for all this is to allow for "quiet" air up before taking off. If the compressor is noisy, maybe not as loud as a 2 stroke bus motor, it's really not addressing the problem. Maybe you don't need a tank at all, just pump into the bus air system. The reason for the tank is reserve capacity and filling up the bus is going to keep the pump going all the time anyway, the tank is doing nothing.

Still might be nice to have the tank and compressor for other tasks. Need to ponder more.

gumpy · August 13, 2017, 05:00:08 PM

Quote from: windtrader on August 13, 2017, 01:27:53 PM
The reason for all this is to allow for "quiet" air up before taking off. If the compressor is noisy, maybe not as loud as a 2 stroke bus motor, it's really not addressing the problem. Maybe you don't need a tank at all, just pump into the bus air system. The reason for the tank is reserve capacity and filling up the bus is going to keep the pump going all the time anyway, the tank is doing nothing.

Still might be nice to have the tank and compressor for other tasks. Need to ponder more.

Install it in a bay so you can unlatch it, unplug it from the bus air system, and take it where you need air for other things. Sometimes you need air farther away than you have enough hose for.

buswarrior · August 14, 2017, 04:08:38 PM

Aux compressors and their install need to be designed for getting the moisture out.

There's nobody in the lower 48 that can escape a freeze, and the wails of "my bus won't air up" follow right behind.

You have to leave a way to drain the discharge muffler in an MCI, if you choose to add the airline at that point.

Self inflicted wound.

Used to be right up there with Treason, but maybe there's a medal for it now?

Get the water out, keep the water out, drain regularly.

Winter is coming, you've been warned.

happy coaching!
buswarrior

windtrader · August 14, 2017, 08:37:09 PM

QuoteGet the water out, keep the water out, drain regularly

Are you talking about water from an auxiliary compressor? Water generally collects in the tank. If running the compressor directly into the bus air system, there doesn't seem like there would be an moisture issue. It might be a good idea to have a valve to let the air vent first, then switch it in line once it clears out.

I'm liking the idea a lot since I was about to chuck a very nice but old Craftsman compressor which will fit nicely without the tank.

Dave5Cs · August 14, 2017, 09:22:29 PM

Don, short answer Nope. Any time you have a device taking in ambient air and basically squeezing it by pressurizing it, it will produce condensation because it heats it up hotter than the outside air it took in originally. That is why most of the buses have air dryers which helps but you still get some water in the systems. You will see when you drain your tanks on the Bus. You have 4 of them.

bevans6 · August 15, 2017, 11:13:29 AM

If you inject air directly from tank-less pump head into the bus through the ping tank, the ping tank will trap the initial water condensate. You can drain the ping tank easily if you keep the valve on it. From there the air goes to the air dryer which will trap the rest of the condensate - the air will be quite cool by the time it gets there and you just need to remember to pump up high enough to cycle the air dryer every once in a while if you aren't running the bus engine enough to do so. Any trace water left gets caught in the wet tank. It's a good system.

buswarrior · August 24, 2017, 09:14:00 AM

Yes, the air drier will take some more moisture, but only up to a point...

First, the coach air system has to be in "loading" configuration, air compressor governor signalling the air drier that the air compressor is going to start pumping, otherwise the purge valve is open, and the input into/through the air drier is closed.

That is usually taken care of by our leaky teakies... the air has leaked off, and it is conveniently and invisibly in "loading" configuration, and it works, but we don't know this is lurking.

Second, the air drier has limits. Somewhere in the dark recesses of my mind.. nope, not sure anymore, (maybe 10 cubic feet?) (and the info is hard to find) there are only so many cubic feet of air you can put through the air drier, and it will be saturated, hence the purge cycle on governor/compressor cut-out.

Here's the scenario: Proud busnut has air drier, doesn't bother draining tanks, cuz nothing comes out anyway. Reads about aux compressors and sets it up to pump in through the "drain daily" plumbing. Doesn't leave facility to "drain daily". Fills the discharge muffler completely with water during the use of the aux compressor and the coach air compressor, no way to empty it. Further, when on the aux compressor for awhile, saturates the air drier with moisture, so damp air is reaching the wet tank, on the aux compressor alone.

Now, the big engine gets started. there is some combination of wet air used to air up the coach to go for a drive. There has been no drying of this build-up air, as the discharge muffler is topped up with water, the air drier is saturated...

The air system reaches cut-out, the air drier has a mighty sneeze, and it is ready for another go. But, the discharge muffler is still full of water, and water has passed to the wet tank.

If the proud busnut continues to ignore the wet tank, because it was always empty... or perhaps worse, relies on automatic drains, or has a cable drain, but doesn't get down on one knee and WATCHES what comes out.... blissfully unaware, the proud busnut heads into the cold weather....

If left unattended, the moisture in the wet tank migrates deeper into the air system, and now there's a mission critical brake valve with a little lick of moisture on the seat... the discharge muffler is full of water, and by association, the copper piping between the compressor and air drier...

Then the cold snap hits.

And there is a screaming post about unable to air up, unable to move, can't release the parking brakes, can't get out of here, I want to move further south... wait, I'm already in Florida/Arizona/California...

There is no where that doesn't see a freeze now and again, in the lower 48.

And all the remedies get trotted out, few of which actually work, and the day warms up just enough... and we think the remedy worked, and we type it again next year for the next newbie.

Keep the water out, get the water out, watch the water leave.

24/7/365

Follow good air system maintenance habits and design, and you will laugh, nervously, when you see the "I'm frozen up" posts in a few short months from now, and enjoy functionality.

happy coaching!
buswarrior

windtrader · August 24, 2017, 09:13:39 PM

BW,

Embarrassed to say I don't know what to do to clear water from the air system. It was a topic not covered when I got the bus.

What tasks do I need to add to my pre trip checklist, currently I don't check any air system status except for enough air to operate the brakes?

eagle19952 · August 24, 2017, 09:47:59 PM

Quote from: windtrader on August 24, 2017, 09:13:39 PM
BW,

Embarrassed to say I don't know what to do to clear water from the air system. It was a topic not covered when I got the bus.

What tasks do I need to add to my pre trip checklist, currently I don't check any air system status except for enough air to operate the brakes?

air system maintenance begins post trip...u drain the tanks.

chessie4905 · August 25, 2017, 03:26:06 AM

They make automatic condensate drains you could connect to compressor or coach tank drain port. Just remember it creates another place for a slow air leak down the road.

scanzel · August 25, 2017, 03:29:03 AM

Be care full with the oil less compressors, you need to check their duty cycle to see at what percentage they run before they crap out or over heat. I bought a Via Air 24v 100% duty cycle to keep my air lock front door aux air tank up. With it running a few times a day it failed just after the 1 yr warranty. When I called Via Air they wanted $45 to look at it plus parts plus shipping to and back. I paid over $200 for this and it failed within a year. Took it apart and it looks like the piston ring wore out and would not compress air any more. I had another oil less by Senco for my little nail gun it also failed the same way. Finally went with an oil filled compressor, still noisy but will probably last longer.