Air compressor trouble

[John316]

Yes, today is a bus working day. Hence the posts.

My question is, how can I test my air compressor to make sure it is working right. I was watching a thread a while back about replacing the a/c, and that still didn't answer some of my questions.

Also, the bus airs up within DOT specs. However, it doesn't air up as quickly as it used to. I did just service the air dryer, so that is now good.

My question is, what can I do to check and see if the compressor is working like it should? I know the DOT specs, but from dead zero, how long (at regular idle) should it take to air up (that includes airbags, all tanks, etc). I don't have an air compressor that I can use to air up the bus, that is big enough. I just have a little one. Otherwise, if I had a big one, I could use that to test and see whether the air compressor is airing things up as quickly as the shop air. Alas, that isn't an option.

Ideas?

God bless,

John

[bevans6]

From dead zero my bus, MC-5C, no tag axles, stock airbeams, DD3 systems, takes 8 minutes on a warm day.  That's running at low idle till air pressure  builds enough to activate the high idle cylinder.  The best test is still the DOT  test, for compressor function - bring the bus up to full pressure, with the engine running on high idle or 1000 rpm fan the brakes  to lower pressure to 80 psi, then time how long it takes to build from 85 psi to 100 psi.  Mine takes 17 seconds. 

Variables will be the condition of your compressor, obviously, how big the sum of all of your air tanks and air bags are for the initial fill from zero, for the DOT test how big your dry tank is and if all your check valves are working right.

As you pump up from zero, you should see a stall in the rise of air pressure around 60 psi.  Below 60 psi the pressure protection valve is supposed to block air from entering the accessory and parking/emergency tank (if DD3), so you see pressure go up to 60, then the accessory tanks fill, then the pressure starts to go up again.  That's if your system has a PPV.

Brian

[Just Dallas]

Removed

[bevans6]

I had another thought, and a comment on Dallas' point about oil.  My MCI has a very small tank called a Ping tank, or discharge muffler, connected directly to the compressor outlet.  It seems to catch any oil and actual fluid that is thrown by the  compressor.  Good thing to check also, after operating the bus for a couple of hours.

But the thought I had was about rpm levels.  You said you wanted to test at low idle.  I'm thinking that a compressor will want to be running at a certain rpm before it gets into it's zone as far as delivering it's rated CFM of air.  Low idle may not do it.  All test that I have read of ask for high idle or 800 to 1,000 rpm, that's gets the compressor into it's operating zone.  Tests at low idle may not actually offer any comparative data.

Brian