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Old 10-12-2019, 06:49 PM   #1
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What is the average air pressure bleed down time

I have always heard a little hissing from by air system when i turn off the coach, but it seams more noticeable. On our last trip i thought i would time how often the air pump is cycling. So the pump kicks in at about 90PSI and kicks off at 120PSI.

driving down the road as speed without any brake application, its cycling about every nine minuets.


Is that in the normal range?



Now that my season is almost over, i will make this a winter project if its out of line.



If i turn the coach off after it being aired up, it will slowly bleed off to about 60psi and it will hold that for quite some time.


I have not crawled under with a water bottle but the sound seams to be coming from either the rear air tank or the rear brake actuators.



Thoughts?
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Old 10-12-2019, 07:57 PM   #2
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Havenít looked at the gauges recently but my air bags will stay up for couple weeks. If I stop overnight I still have almost 100 lbs or so. I will have to look next time we go out.
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Old 10-13-2019, 02:52 PM   #3
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I have the same question. My RV looses most of its air pressure overnight. I went underneath with a spray bottle of soapy water and did a quick check. I only found one leaking connection, which I tightened. Still looses most of its pressure overnight. What is "normal"?
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Old 10-13-2019, 02:59 PM   #4
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If i turn the coach off after it being aired up, it will slowly bleed off to about 60psi and it will hold that for quite some time.

I think your front and rear tanks should have Pressure Protection Valves that shut at about 65 psi, so this makes sense.
9 min between compressor loading cycles seems pretty good to me.
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Old 10-13-2019, 05:14 PM   #5
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A little bit of an update. I did some tests today and went underneath to find leaks. First the air that I could hear from the passenger rear side was air escaping from the leveling valve. after it was aired up motor off air was escaping from the vent tube of the air leveling valve. On my XC chassis there is one on the Right rear and two up front. only the rear was leaking.



I the part is approx 150.00 to replace but i also found this video as to how to repair it, I have the haldax valve and come to find out its two shrader valves, so i am going to try that next.



video


The testing i did on the system you can find on line. I am not sure if leveling issue is the only problem maybe someone with more knowledge can respond.



I did the one Min. test where you air up the system turn off the motor, turn on the key, to watch the a gauge and then apply the brake and hold for one Min. after the initial air drop its only supposed to lose 3 lbs or less, in my case it lost about 15lbs after the initial drop.



I am thinking that i could also have a leaking brake chamber but not sure. I could not hear anything near the brake chambers. I did find a video on how to replace the diaphragm in a brake chamber but its not simple and i want to make sure that is what I need to do.



The other test i did was to air it up and turn off the motor, turn on the key to monitor and I lost 15psi in the first 3-4 min. but then it held that pressure for 10min. and It took another 20 min. lose another 5psi, over 30 min.



I did get under the coach with s soap water bottle and could not find any leaks in the lines or connectors so I think my issue is ether leveling valve or brake chambers.
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Old 10-13-2019, 05:56 PM   #6
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Good video, thanks for posting that.
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Old 10-14-2019, 04:10 AM   #7
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The air compressor is not designed at a 100% duty cycle, in that it can run all the time.
In all applications the compressor has been designed on a 15% duty cycle... in that it can run 15% of the time... The problem that occurs with constant running is the excessive heat from compressing air... this heat can't be removed with the water cooling system in the compressor...
With all this said.... most good truck/rv air brake systems will hold air at least 24 hours.. in that 24 hours later you have enough air to start the engine, and you have the 65 psi required to release the parking brake and drive away. My RV will hold good air pressure for usually 2 days or so...
I'm now retired but I used to do business with powerbrakes.com, a family owned company that works in the Hydraulic and Air Brake business.... they both offer new valves and other accessories in new and re-manufactured products... These are nice people, have excellent phone skills...
With all that said... I don't hear well, so when I have an issue with air brakes I get out my trusty soap and water in a spray bottle and run the system...
One last thought... water is the biggest problem in the system... know how to drain your air tanks, know how to change the dryer cartridge in your RV and keep the system dry.... excessive moisture will limit braking potential by taking up space in your air tanks... water/moisture will rust the tanks from the inside out.. and damage some of the working surfaces of the valves where they have to seal...
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Old 10-16-2019, 10:11 PM   #8
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Believe it or not, the Freightliner spec for air reservoir leaks is a maximum of 2 pounds per MINUTE! In other words, your 120 psi air tanks could leak down to zero in an hour and thatís OK.

My air tanks will leak down to almost zero overnight, however the suspension will still be up on air. The suspension will take about 2 days to leak down to zero.
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Old 10-17-2019, 04:30 AM   #9
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I am planning to replace this leveling valve this weekend. I called FL to get the Ride Height spec for my coach. Its 10 1/4 inches +/- .5 he said, from the bottom of the frame rail to the center of the lower shock bolt. Mine is a inch low out of the spec. After I get the valve replaced i will look for other leaks.
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Old 10-17-2019, 05:22 AM   #10
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Hopefully you're properly blocking the coach while you're underneath checking on things. More than one coach owner has been killed while working under a coach which suddenly lost air and fell on him.

This is even more important if you're doing anything related to the suspension system. Push the wrong thing, aggravate a leak by poking around, or do any number of things and suddenly your coach can drop on you.

Many use their leveling jacks to support their coach while under it, but they are not designed as safety devices.

Please read your manual and be sure that you're supporting the coach properly.
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Old 10-18-2019, 08:41 AM   #11
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Hopefully you're properly blocking the coach while you're underneath checking on things. More than one coach owner has been killed while working under a coach which suddenly lost air and fell on him.

This is even more important if you're doing anything related to the suspension system. Push the wrong thing, aggravate a leak by poking around, or do any number of things and suddenly your coach can drop on you.

Many use their leveling jacks to support their coach while under it, but they are not designed as safety devices.

Please read your manual and be sure that you're supporting the coach properly.


Very good advice.
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Old 10-18-2019, 06:24 PM   #12
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Yes i have followed the directions to the tee, when installing the leveling valve, It calls for blocking the wheels and then dumping the air, I was mostly working at that level but did place jack stands under it also even though the air was dumped.



It was a successful day. I was able to fix my leak, the rear leveling valve was leaking badly. It was difficult to reach but doable. once i installed it one of the push lines was leaking so i had to make a run to Napa but i was able to get it all back together.



I was also thinking I may have a bad brake chamber, but I check both the service brake chambers and the two spring brake chambers and all were good.



I did find a few minor leaks around the rear relay, but those can wait till winter. I am holding air now.


The other issue was that when i set the ride height i notices i was almost an inch low, now i am right at the spec.

Its satisfying to figure out how to do this stuff. Thank goodness for YouTube.



I will report back in about a week when i take a trip and compare the improvement in the cycle time on the pump.
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