Air Issue Sometimes

[Jim Eh.]

You may want to check you brake adjustment. If you are consuming a large amount of air by using the brakes while maneuvering, excessive brake stroke will eat up the reserve air pretty quickly while the RPMs are low and the system not building very fast.

[Melbo]

Alright I took everyone's advice and replaced the unloader valves and adjusted the brakes.  I also picked up a regulator that I have not installed ( don't think I need it but I will have it if I do ) Then I tested and it aired up just like before.  I have not had it on the highway again.  That will be thursday and I will let you know how it does.  Thank you for the information and suggestions.

Melbo

[bevans6]

To be honest it sounds quite normal to me, except for the long compressor recovery time.  40 seconds might be the maximum, but mine recovers in around 15 seconds.  Useful tests that I do every day I drive the bus:

One:  recovery test is done with the engine at high idle or 1000 rpm if no high idle, it is not done at normal idle.
Two:  with all suspension and other air systems fully up to pressure, measure pressure drop with engine off.  No more than 3 psi per minute allowed.
Three:  As above, engine off, foot brake fully applied, measure pressure drop - again no more than 3 psi per minute allowed.  DO NOT MOVE your foot from fully applied - even the slightest relaxation of pressure will release air from the exhaust valve and give an indication of a leak.

When the governor turns the compressor off and opens the purge valve on the air dryer, it does this by sending air pressure to both devices - the unloader valves and the purge valve.  Either can leak when the air pressure is slowly declining from 120 psi cut-out pressure to 95 psi cut-in pressure.  As soon as the governor gets to cut-in pressure, that leak will stop, since the governor exhausts the air it was using to hold the two devices open.

I really quite enjoy these threads, keeps me current on air systems 101... 

[Melbo]

Thank You Bevans

I don't have a fast idle with the L10 so I am sure the idle is much below the 1000 rpm you mention.  We are off on a road trip so I will have multiple opportunities to check how the air system is working.  I did a bunch of maintenance on it last summer.  I will keep you posted.

Melbo

[buswarrior]

40-50 seconds at base idle sounds fine to me.

Let us know if your air consumption while making manoeuvres has changed. Did you measure the brake stroke before you adjusted 'em?

Sometimes, drivers use too much pedal when manoeuvring, be conscious of keeping the pedal travel only as deep as necessary to get a stop, no deeper.

Happy coaching!
Buswarrior

[eagle19952]

Mel has a Cummins engine with the PT pump they do need to be timed the pump is driven off the compressor

Never did like that set up. What were they thinking ?
Changed a few of them at 20 below...on the side of the road.

[buswarrior]

All in a row Cummins accesories...

Gear train for all that also limits the size of compressor you can employ...

We looked into upsizing the compressor in a transit application, trying to defend against constantly being cut-in...

No can do.

In choosing engines, if it ain't one thing, it's another?

Happy coaching!
Buswarrior

[chessie4905]

You've got that! Series 60 were supposed to be the best thing since sliced bread. Then Bull gear goes out in high miles.$$$. All of them have their particular issues.

[kevink1955]

I am not sold on the 60 series, here are some photos of the damage to a low miles fire truck engine.  we still have a few 6V92's that are much older and have never been worked on internally. could not post more pics but the pic of the head looks like it lost a valve head

[Jim Eh.]

"Well I pulled the discharge line and it is not oily and seems to have pretty good air pressure."

Mel, when you pulled the discharge line off the compressor to check it for oil did it continually to leak from the tank side or just what would be in the line (if any)?

[Melbo]

Jim I removed the air supply to the bus and checked for any oil residue and found nothing so I started the bus up and checked the air supply pressure and it was comparable to an electric air compressor as near as I could tell so I reassembled everything and went about my business.  After I got a chance and changed the unloader valves , adjusted the brakes, and took some driving tips from members of the board here everything is operating EXCELLENTLY.  I want to thank you all for the tips and information.  Here's hoping I don't have to change the air compressor on the side of the road at 20 below.  In fact if I am ever someplace that gets to 20 below it has to be a really bad mistake.  I'm typing this as I am sitting on the beach in Mexico.

Thanks again

Melbo

[Oonrahnjay]

... everything is operating EXCELLENTLY.

      Good news!  It's always good to hear the success stories.  Good luck with keeping things working right for a long time.

...  if I am ever someplace that gets to 20 below it has to be a really bad mistake.  I'm typing this as I am sitting on the beach in Mexico.   Melbo 

      Amen, brother!