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GR "Scott" Cundiff

DP Air System Questions

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Excuse the basic questions, but running a rig with air brakes/suspension is new to me.

1. When I shut the rig down and press the dump air switch, the air is pretty slow to go down - and the gauge never really goes below 40 pounds or so.  Is this normal behavior?

2. After first starting up the low air alarm sounds until, I think 80 pounds.  I know that's expected.  Is there any way to acknowledge that alarm and silence it?  That minute or two seems kind of long with that beep, beep, beep.  :)  

Thanks in advance for any helpful and patient responses.

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Most air systems leak down over time.  How long or short of a time will depend on how big or small the leaks in the system are (pretty much all systems leak).  If yours leaks down to 40 psi and then holds there, that isn’t too bad.  This is assuming it doesn’t happen rapidly.  Mine will eventually leak down to 0 psi, but it takes a couple of days.

There is no way to silence the low air alarm.  This is a safety feature and must not be bypassed.  

You need to learn how to conduct an air brake test on your vehicle to make sure the system is functioning properly.  The test should be done regularly to make sure the system functions and there are no changes to it.  If you do not know how to do this, I can provide a document that will walk you through how to conduct one.

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Not withstanding getting familiar with an air brake test and doing it, I don't think it applies to what he is asking.  

When you are setting up camp and manually dump your suspension air it may not go all the way down depending on your chassis and how it is designed.  I would think yours is probably normal and working the way it should.

As far as your low air alarm it is just something you have to deal with.

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The point I would make is anyone with air brakes should understand the system. I might be in front of him some day.

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Thanks folks - yes I was asking about dumping air.  I hold the dump air switch down and the air slowly drops to around 40 pounds and settles there.

Okay on living with the low air alarm.  I was hoping there was some way to acknowledge and silence it.  

I have the Texas DPS Commercial Manual - and am just starting to work through the chapter on air brakes.  I also have a pretty robust section on air brakes in my MH owner's manual.  I imagine I'll need help from someone before attempting to drain the system.  I have a neighbor who does a lot of his own maintenance who happens to own a rig similar to mine.  

Thanks again for putting up with the questions of a novice.

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Draining the tanks is painfully easy. There should be a lanyard attached to a valve on the bottom of the tanks. Pull the string, bleed until no moisture comes out, release. In the event your drain valves don't have a lanyard, then you get to crawl around under the rig, and manually turn the valve handles.

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Do you have air leveling or jacks (either electric or hydraulic)?   How much you dump is dependent upon how the leveling system is set up.

IIRC they don't do the air brake test for Class B non-CDL licenses.  Notice I said, if I remember, because it has been YEARS since I took my test (2006) and since we have hydraulic brakes it was a non-issue for us.

When we get read to leave, the LAST thing we do is starting the engine and retracting the jacks.   The alarm goes off because the levelers are down in addition to the air bags filling.  But that's ok, because I'm out the door collecting the pads underneath the jacks, and the air bags usually are full before the jacks are all completely up.  

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10 minutes ago, GR "Scott" Cundiff said:

Is pressing the brakes while holding down the dump air a good idea or not?

Why would you do that?  

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I suppose so, again we have hydraulic brakes so I would have no experience with this.  Why the hurry to dump air?   Also, do you have a system for automatic leveling that would dump air as needed?  

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13 hours ago, GR "Scott" Cundiff said:

. When I shut the rig down and press the dump air switch, the air is pretty slow to go down - and the gauge never really goes below 40 pounds or so.  Is this normal behavior?

Our DP exhibits similar behavior.  The question I have is why do you care about taking the pressure below 40 psi?  AFAIK the only reason to dump air is to take the strain off the airbags and bring the coach a bit lower to the ground for leveling purposes. I usually get the pressure down to around ~60 psi and don't even attempt to drop it any further.

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37 minutes ago, docj said:

Our DP exhibits similar behavior.  The question I have is why do you care about taking the pressure below 40 psi?  AFAIK the only reason to dump air is to take the strain off the airbags and bring the coach a bit lower to the ground for leveling purposes. I usually get the pressure down to around ~60 psi and don't even attempt to drop it any further.

Thanks.  I don't "want to" I just want to know if this is normal behavior or if it is something I need to be concerned about.  Apparently, it is normal.

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Set the parking brake and then take foot off the brake pedal. Holding your foot on the brake won’t make it bleed down any faster and pumping the brake is a pain. It sounds like you have a knob you have to hold down to bleed down the suspension. Am I right? You can also look for a lever that will say something like suspension. That will dump your suspension without emptying your air tanks. You may have 3 tanks. You will have a lanyard for each one. You only pull it until the liquid stops coming out. If it is oily, you may have bad seals in your compressor. I have never gotten anything except air out of my tanks. 

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3 hours ago, Ronbo said:

Set the parking brake and then take foot off the brake pedal. Holding your foot on the brake won’t make it bleed down any faster and pumping the brake is a pain. It sounds like you have a knob you have to hold down to bleed down the suspension. Am I right? You can also look for a lever that will say something like suspension. That will dump your suspension without emptying your air tanks. You may have 3 tanks. You will have a lanyard for each one. You only pull it until the liquid stops coming out. If it is oily, you may have bad seals in your compressor. I have never gotten anything except air out of my tanks. 

Yes, a switch you hold down to "dump air."  

And thanks for the help via the phone!  Take care.

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Did the OP explain why he was dumping his air? Is this a requirement with some DP’s?  Is this necessary when using air to level the coach? What if you have hydraulic leveling? Just curious? TIA

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Assuming I understand your questions correctly I'll attempt to answer. When you push the button to dump the air  (This is dumping air from the air suspension) the air gauge will not go to zero because this does not dump air from your braking system, only the air suspension. This is normal operation. There is no need to hold the air dump button down, a simply press will suffice to trigger the solenoid that opens the air dump valve, IF it is operating as designed. When you use the automatic level function, the system should automatically dump the air suspension, then proceed to level the MH, and automatically shut off when level is obtained.

When you read and understand the procedure for performing an air brake check you'll understand why the low air warning buzzer sounds and when, and when it is designed to stop sounding.

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10 minutes ago, Ray,IN said:

Assuming I understand your questions correctly I'll attempt to answer. When you push the button to dump the air  (This is dumping air from the air suspension) the air gauge will not go to zero because this does not dump air from your braking system, only the air suspension. This is normal operation. There is no need to hold the air dump button down, a simply press will suffice to trigger the solenoid that opens the air dump valve, IF it is operating as designed. When you use the automatic level function, the system should automatically dump the air suspension, then proceed to level the MH, and automatically shut off when level is obtained.

When you read and understand the procedure for performing an air brake check you'll understand why the low air warning buzzer sounds and when, and when it is designed to stop sounding.

Thanks Ray - I may have been mistaken about needing to hold the dump air button down to keep it dumping air.  I'll check it out the next time we travel.   However, the manual says specifically that you are to "hold the Air Dump switch to lower the suspension."

Our leveling system is powered but manual.  The manual for the rig says I need to manually dump air to lower the suspension before using the leveling system.

I understand the purpose of the low air warning buzzer, I was a bit frustrated because I wanted to hear what the engine sounded like as it was just starting and I couldn't hear it for the buzzer.  No biggie - I just wondered if there was a way to acknowledge the low air.  As far as I'm concerned we can drop that part of the conversation as I understand the importance of the rig's air pressure coming up before proceeding.  

Edited by GR "Scott" Cundiff

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Scott I may have assumed too much, as not all leveling systems are HWH brand, which is what I was describing when talking about the dump valve button. Its best to follow your instruction manual.

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Scott, if you could include your coach information in your signature it might help with questions like this one. Our coach, for example, has a HWH leveling system, but NO jacks. It uses the air bags for leveling. If we're just spending one night I just do the automatic leveling and let it go at that unless we're so far off that I need to get out some boards. When we're landed for several days or more, I put on the tire covers, dump the air, and then level. That means that the coach body is resting on one or more tires (which is why I put the tire covers on first). That makes for the lowest step.

Dumping the air, in our case, is just dumping what's in the bags. The tanks are still full. They will eventually go down, but I don't worry about that. That's normal. As you can imagine, the air rushes out at first, but as the pressure in the bags drops it slows down. Again, that's normal.

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1) I don't air down.  Would though if I had small children on board with a concern of pushing the parking brake while parked.  I probably should air down once and awhile to check my low pressure alarm and spring brake activation.

2) I'm not aware of being able to shut off the low air warning.  If I could, I wouldn't because I'd likely forget to turn it back on afterwards.  Leaving it off would cause some problems if my air system was compromised during transit (spring brake will be activated and will lock up the brakes if pressure drops too low).

If you have a fast idle option, it would quicken the air up time at startup.

Edited by Ro and Joe
Fast idle suggestion added

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