Maintaining pressure while parked

[5TID]

How long should my tanks maintain pressure while parked? I know ideally there are no leaks and it is infinite, but in reality what is a usual time to drop from 120psi to 60psi to 0psi? I know of a few minor air leaks on my truck and debating if I should fix them due to the cost and effort involved. Right now, I can park for and hour and have no problem starting it up and going right away without having to wait for air to build. Not sure of the exact time that is valid for, but I know it is less than 4 hours. I'm not expecting a week, or really even a day (will build air while it warms up anyway), but would like it to last as long as the truck is more or less warmed up and be driven right away.

 

[msgjd]

How long should my tanks maintain pressure while parked? I know ideally there are no leaks and it is infinite, but in reality what is a usual time to drop from 120psi to 60psi to 0psi?

being you have the commercial-type air brake system , there are specific rules and regs, and simple step-by-step tests to determine allowable air losses .. I used to know and practice them daily before I retired, and this info can be found on the FMCSA website instead of me regurgitating it here, perhaps with an error .. These simple pre-op and during-op tests can determine existing problems as well as future potential problems than the ones we usually think of ..

1: There is "what is legal" as far as a commercial carrier, and then there is what is "gotten away with" by some of them, and some of us who drive our rigs only on occasion around town ..

2: There is a certain liability in anyone who answers your question, thus I suggest you look up "the right & legal way" on the FMSCA website, including the simple testing steps you do in-cab, etc ..

4: I will tell you what I have done although it's wrong to be loose with the fine line of acceptable/unacceptable air loss when it comes to commercial or hobby operation. .. Thus, although what I say I do here is wrong, even in non-commercial use, in engine-off mode I get concerned when I have lost all pressure after 2 hours .. When I lose all air after an hour, I have an all-around look-see.. And of course immediate attention if there's an audible leak or if all air is lost within an hour.. I am happiest when, as Mullaney has said, I can jump in the next day and although the pressure has gone down some, the buzzer doesn't sound .. That would be the ideal situation, however, in the everyday commercial world, most-especially with air bag suspension, air-ride cab, air dump & pto controls, air environmental controls, etc, that perfect "buzzerless' overnight situation doesn't happen often, although the truck passes its allowable daily air test

3: We all should perform the usual FMCSA pre-op/during-op brake system tests, regardless whether or not we have a toy, because these tests may show other issues in the system that we cannot hear/see, such as a bad check valve, for example, where air bleeds off on the "park" side of things where it shouldn't be

 

[Mullaney]

How long should my tanks maintain pressure while parked? I know ideally there are no leaks and it is infinite, but in reality what is a usual time to drop from 120psi to 60psi to 0psi? I know of a few minor air leaks on my truck and debating if I should fix them due to the cost and effort involved. Right now, I can park for and hour and have no problem starting it up and going right away without having to wait for air to build. Not sure of the exact time that is valid for, but I know it is less than 4 hours. I'm not expecting a week, or really even a day (will build air while it warms up anyway), but would like it to last as long as the truck is more or less warmed up and be driven right away.

.
First, @msgjd is "dead nut on" with his suggestion that you use the FMSCA website and spend a little time reading. There are rules even though we aren't "commercial" vehicles and having a truck that won't hold air is a bad thing.

What you really need is to have your truck turned off - to make it quiet. Do you have "house air"? Some sort of external air source? If not, the only choice you have is crank it, let it build air and then crawl around under the truck listening for leaks. A spray bottle with some Dawn dish detergent mixed into water and spraying every air line you see will help you fix the leaks.

MY OPINION is that you should be able to come out in the morning and crank the truck and not hear the low air buzzer. I have four trucks with air brakes. All four of mine behave that way. All of them had some sort of leak when I got them and the soapy water found everything from tiny little leaks to full out "bubble explosions" when I started my repairs.

The plastic line (material) is cheap. The ferrulls and compression fittings are not cheap. You need to use (purchase) DOT Approved parts. NAPA or TruckPro are good sources.

 

[5TID]

Thanks for the replies. I have done the soapy woder trick while plugged into house air. The only two places I can hear air is from the park brake air switch and the front axle engagement switch.

I guess I really do need to time it and verify how long it maintains air.

 

[Mullaney]

Thanks for the replies. I have done the soapy woder trick while plugged into house air. The only two places I can hear air is from the park brake air switch and the front axle engagement switch.

I guess I really do need to time it and verify how long it maintains air.

.
My first leak was just plain "old age". The Wet Tank (driver's side closest to the step) was rusted in a bad way. Truck is almost 40 years old and that is way beyond its expected lifetime. Road salt maybe, but it could have been regular old dirt that collected over the years.



Spraying the air tanks where there are no fittings is a worthwhile exercise.

.

 

[5TID]

Did some testing, after 1 hour and 15 minutes, pressure dropped from 115psi on the gauges to 70psi. I also let it sit over night and while the gauges read 0/10psi, the drain valves all released pressure when I open them this morning.

I have a new front axle switch on the way, but I think the bigger culprit is the park break switch. Have not been able to find one yet, so might need to try and rebuild the one I have.

 

[Mullaney]

Did some testing, after 1 hour and 15 minutes, pressure dropped from 115psi on the gauges to 70psi. I also let it sit over night and while the gauges read 0/10psi, the drain valves all released pressure when I open them this morning.

I have a new front axle switch on the way, but I think the bigger culprit is the park break switch. Have not been able to find one yet, so might need to try and rebuild the one I have.

.
Rebuilding might be possible.

Maybe a picture of your "park brake switch" might be good.
Just to make sure you are talking about what we think you have.

 

[5TID]

Parking brake switch with roller lever triggered by parking brake lever (blue arrows). Red arrow is where air is escaping (pivot point I think).

 

[Shirehorse]

Most of us delete the front axle engagement valve from our transfer cases (the one that trips on a large washer to auto activate 6x6 in low range). If you do the same, that valve can be repurposed for your parking brake in-cab.

 

[Karl kostman]

Air leaks are pretty much just another maintenance item, I have yet to have one that was more than 100$ to fix and since I do all my own work thats just for the parts. Its all pretty simple, I have my air parts box where I stock a few lengths of airline and a few set of ends and that pretty much is all it takes. Now if you have a treadle leaking those can be replaced, I do not know cost on that but I also believe they can be rebuilt. I had developed a larger air leak in my HEMTT and I pulled into a buddies shop to just park it there and after I shut the truck off crawled around under the truck and found the leak, got a ride home and grabbed my kit and had the truck fully operational an hour later. Sometimes it all sounds harder than it really is!