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Topic: Air Pressure down to 2psi overnight (Read 2085 times) previous topic - next topic

Re: Air Pressure down to 2psi overnight

Reply #40 –
Quote from: wolfe10 –
Leak, plus, perhaps bad check valve.
Found leak at T fitting that seems to have slowed things down, but air still will go down into the 40's overnight and I read or heard somewhere that the check valve should stop it at 60psi - is that correct

Re: Air Pressure down to 2psi overnight

Reply #41 –
Quote from: jimgior13 –
I read or heard somewhere that the check valve should stop it at 60psi - is that correct

In short yes the isolations valve should close at about #60.  They (our coach has 2) are located on the front and rear tanks, which both are located up front.

I just saw you post about the governor from 3 weeks ago. In general  Bendix D-2 governor different numbers are from part number changes over the years, whether the set point is adjustable or not, and what the set point is out of the box. Now cut in/cut out span is around #20 and is not adjustable.  Cut out/cut in can be like #105/125 or 110/130 out of the box so they have 2 different part numbers. So any good truck parts store will have one on the shelf just ask for a D-2.  Have you noticed what your cut out/in pressure has been?  If so ask for one that is close to what you have saw on the dash gauge.

Mike

Re: Air Pressure down to 2psi overnight

Reply #42 –
Quote from: jimgior13 –
I read or heard somewhere that the check valve should stop it at 60psi - is that correct
Do you have a air system schematic for your coach?  If so, you need to study it so you understand the flow of air in the system.  Doing so makes it much easier to diagnose problems and narrow down the possible location of air leaks.

The diagram below is a good "generic" depiction of a air system on a coach with tag axle and slide(s).  It may not be exactly like your newer 2009 Nimbus, but it is probably similar.

If you reduce the air system down to the most basic components, you have the air compressor, the air dryer, the wet tank, and the 2 brake tanks.  Everything else is ancillary.  The dash pressure gauges read the brake tank pressures, because they are the most critical tanks.  They power the brakes.  The brakes save your butt.

Each brake tank has 2 "check" valves.  The inlet check valve keeps air pressure from escaping "backwards" in case of a big air leak UPSTREAM of the tank.  The protection valve is designed to retain a minimum of 60 psi in the brake tank in the event of a big air leak DOWNSTREAM of the tank.  60 psi is enough to provide braking so you can get the coach to a safe place to park.  It also is enough pressure to keep the emergency spring brakes from activating.  Hence the name "PROTECTION VALVE".  They protect you in a emergency.

If you start out with full pressure (120 psi) in your air system, and after a short time (one night) your dash air gauge shows pressure below 60 psi, then you could have a leak either upstream OR downstream of the brake tanks.  You don't know which check valve is malfunctioning.  The only way to further pin down the leak location is to replace the check valves.  Once you know both sets of check valves are holding THEN you can go hunting for the leaks.

Re: Air Pressure down to 2psi overnight

Reply #43 –
Quote from: Chuck & Jeannie –
Do you have a air system schematic for your coach?  If so, you need to study it so you understand the flow of air in the system.  Doing so makes it much easier to diagnose problems and narrow down the possible location of air leaks.

The diagram below is a good "generic" depiction of a air system on a coach with tag axle and slide(s).  It may not be exactly like your newer 2009 Nimbus, but it is probably similar.

If you boil the air system down to the basic components, you have the compressor, the dryer, the wet tank, and the 2 brake tanks.  Everything else is ancillary.  The dash pressure gauges read the brake tank pressures, because these are the most critical tanks.  They power the brakes.  The brakes save your butt.

Each brake tank has 2 "check" valves.  The inlet check valve keeps air pressure from escaping "backwards" in case of a big air leak UPSTREAM of the tank.  The protection valve is designed to retain a minimum of 60 psi in the brake tank in the event of a big air leak DOWNSTREAM of the tank.  60 psi is enough to provide braking so you can get the coach to a safe place to park.  It also is enough pressure to keep the emergency spring brakes from activating.  Hence the name "PROTECTION VALVE".  They protect you in a emergency.

If you start out with full pressure (120 psi) in your air system, and after a short time (one night) your dash air gauge shows pressure below 60 psi, then you could have a leak either upstream OR downstream of the brake tanks.  You don't know which check valve is malfunctioning.  The only way to further pin down the leak location is to replace the check valves.  Once you know both sets of check valves are holding THEN you can pursue hunting for the leaks.


Thank you for this

Re: Air Pressure down to 2psi overnight

Reply #44 –
Where is the Rear Air Tank located & best way to access it.  Thanks

Re: Air Pressure down to 2psi overnight

Reply #45 –
Quote from: jimgior13 –
Where is the Rear Air Tank located & best way to access it. 

Raise coach and block with safety stands
Slide under front end where ever is good for you
Set up with your back next to the front axle
Look up to the front of the coach
You will see the 2 matching tanks in front of you just behind the back of the generator
On our coach the rear is the one on the passengers side but yours may be different.

Mike

Re: Air Pressure down to 2psi overnight

Reply #46 –
Quote from: Pamela & Mike –
Raise coach and block with safety stands
Slide under front end where ever is good for you
Set up with your back next to the front axle
Look up to the front of the coach
You will see the 2 matching tanks in front of you just behind the back of the generator
On our coach the rear is the one on the passengers side but yours may be different.

Mike


Thanks Mike

Re: Air Pressure down to 2psi overnight

Reply #47 –
Quote from: Pamela & Mike –
On our coach the rear is the one on the passengers side but yours may be different.
Expanding on Mike's directions, there is one sure way to ID which tank is "Front" and which is "Rear".  It does require that you have the air system diagram for your coach.

When you crawl under the coach, you will notice that most of the air lines in the vicinity of the brake tanks are marked with white tags.  The tags have numbers printed on them.  The tag numbers correspond to the air line ID numbers on the air system diagram.  By matching the numbers on the diagram to the actual air lines, you can positively determine which tank is which.

Note: You can't use the generic diagram I posted earlier for this ID method.  It is not specific to your coach.
 

Re: Air Pressure down to 2psi overnight

Reply #48 –
Quote from: Chuck & Jeannie –
Expanding on Mike's directions, there is one sure way to ID which tank is "Front" and which is "Rear".  It does require that you have the air system diagram for your coach.

When you crawl under the coach, you will notice that most of the air lines in the vicinity of the brake tanks are marked with white tags.  The tags have numbers printed on them.  The tag numbers correspond to the air line ID numbers on the air system diagram.  By matching the numbers on the diagram to the actual air lines, you can positively determine which tank is which.

Note: You can't use the generic diagram I posted earlier for this ID method.  It is not specific to your coach.
Thanks Chuck - I was able to get my air diagram from FOT