Slow air make-up in '87 Prevost

TedCalvert · March 08, 2015, 06:03:36 PM

Good evening. Seems like it takes too long to make air, thinking about compressor rebuild. Not sure yet as to compressor or leaks being the cause, will check further before doing anything. 'da Book says it's a Tu-Flo 100, they are hard to find. Would that be correct? Number seems to be relative to capacity? Maybe this is just the nature of this beast ?

lostagain · March 08, 2015, 06:12:56 PM

Is it freezing where you are? Your profile doesn't show where you are. If so, check the ping tank for ice. Then the dryer. Is the heater at the bottom of it not working? or turned off? If not freezing, you could undo the air supply line at the ping tank to see if the compressor actually makes air. If not, is the compressor gear driven, or belt driven? Is the compressor turning with the engine? Or maybe a check valve down stream in the system is stuck? Tuflo 100 doesn't sound right, it could be a 500, 600, 700.

JC

luvrbus · March 08, 2015, 06:37:44 PM

I think 100 is a typo it should have a Tu-Flo 700 compressor

eagle19952 · March 08, 2015, 06:56:24 PM

Quote from: luvrbus on March 08, 2015, 06:37:44 PM
I think 100 is a typo it should have a Tu-Flo 700 compressor

there is a 1000... not likely here tho ..

TedCalvert · March 08, 2015, 07:22:52 PM

It does make air, but slowly. Always has been slow, even in summer.

My info is from a pre-CAD hand-lettered scanned onto Prevost's website, where I got it. Could very well be 700. I'll go look at compressor tomorrow.

Anyone have one of these buses, are they usually slow to air? Maybe 5 min @ high idle, from clear down not run for 2 months body down on the stops.

luvrbus · March 08, 2015, 07:37:14 PM

5 mins is not that bad when on the stops after 2 months for a Prevost when you have a few leaks, I checked the book it is a Tu-Flo 700 on the back of the 8V92 fwiw and that is 15.5 CFM @ 1250 rpm

Jon · March 09, 2015, 03:29:59 AM

I agree with Clifford. When the bus has no air in it at all there are all the tanks plus all the air bags to fill.

Go for a drive and check to see if the gauges are cycling a lot. That will tell you if the compressor needs replacement or if it is OK. Are you getting a lot of oil out of the dryer or the wet tank? Another sign of poor compressor health.

bevans6 · March 09, 2015, 08:07:14 AM

Time to air up from total run-down is almost meaningless, in terms of a comparison to other buses. You need to fill all the various systems, level the suspension, etc - a lot of air needed. Plus you really can't measure how totally empty it is. A far better test is the DOT compressor recovery test. AFTER the bus is fully aired up, stable, etc, do the pressure loss test. That is observing how much air is lost first with the engine off, the brakes off, then with the brakes full on. Should be no more than 3 psi per minute. Next, with the engine on, fan the brakes to reduce the air pressure to 80 psi. With the engine at 1,000 rpm or high idle, observe the time required for the compressor to recover from 85 psi to 100 psi. That must be no more than 2 minutes, and should be less than 30 seconds. My bus is consistently around 18 seconds. Tank volume plays a big part in this, but the key is around 30 seconds or less and consistent from day to day. This test is required as part of the daily DOT inspection for commercial vehicles.

Brian

robertglines1 · March 09, 2015, 09:27:09 AM

Initial from 0 to 60 lbs pretty quick. After that air is allowed into auxiliary system and initial fill slows down as air tanks for auxiliary and 8 air bags need to be filled. FWIW

TedCalvert · March 11, 2015, 10:07:59 AM

Thanks for all your good advice. It is relatively quick from 0-60 or so, guess I hadn't realized the volume of tanks & bags. I do have some suspension leaks to address. I'm spoiled from driving new J-4500's last year!

TedCalvert · March 11, 2015, 10:08:31 AM

Thanks for all your good advice. It is relatively quick from 0-60 or so, guess I hadn't realized the volume of tanks & bags. I do have some suspension leaks to address. I'm spoiled from driving new J-4500's last year!

TedCalvert · March 11, 2015, 10:09:13 AM

Sorry. Dumb fingers.

luvrbus · March 11, 2015, 11:56:23 AM

I understand the J4500 spoiling you I drove one back from Phoenix for a casino here a nice bus

Oonrahnjay · March 11, 2015, 05:03:09 PM

Quote from: TedCalvert on March 11, 2015, 10:08:31 AMThanks for all your good advice. It is relatively quick from 0-60 or so, guess I hadn't realized the volume of tanks & bags. I do have some suspension leaks to address. I'm spoiled from driving new J-4500's last year!

Yes, do get the suspension leaks fixed. But remember that some buses with larger or additional tanks have "protection" valves. For the first phase, you're only pressurizing part of the system; once pressure is built up in that initial part, the protection valves open and at that point you're filling a larger volume. When this happens, it appears that the process is slowing down but actually the same volume of air is coming from the compressor. The other side of that is that you have a larger volume of air as reserve or to cover unusually large needs.