Air Pissing out

[nbone28]

4 minutes ago, Joey Mack said:

What is the air pressure on the gauge when the drier blows off ? 

believe it’s 160, i’ll have to double check in the morning 

[Joey Mack]

No way.. the pop off in the tank is set to 150..  theres the issue of its 160

[Joey Mack]

If you have 160, you need to look at the pop off valve, and dial the governor down or replace it..  125-140 is good enough

[nbone28]

2 minutes ago, Joey Mack said:

If you have 160, you need to look at the pop off valve, and dial the governor down or replace it..  125-140 is good enough

Will check in the morning, 140 sounds about right. 

[Geoff Weeks]

21 minutes ago, Geoff Weeks said:

You can check another way:

DOT requirements are:

run the truck until the compressor blows off, with the brakes released (chock the wheels) shut off engine. It can leak no more than 3 psi/min per res, so for a truck with a primary and secondary air system, the truck can only loose 3 psi/min from each tank. When the trailer is connected you still can't leak more than 3 psi/min with the brakes released.

F@#$ the pressure for the moment! Will it pass the DOT test?

It is supposed to be done at pre trip, but no one ever does, including myself. I use the "duty cycle" time of the compressor while running down the road. If my compressor has high duty cycle I know I have a leak even if I can't hear it.

If you can't see 3 psi on the gauges, go 2 min and look for a 6 psi drop, or 4 min for a12 psi drop. If you can't tell 12 psi difference on a gauge reading either you need new gauges or new eyes.

[nbone28]

2 minutes ago, Geoff Weeks said:

F@#$ the pressure for the moment! Will it pass the DOT test?

It is supposed to be done at pre trip, but no one ever does, including myself. I use the "duty cycle" time of the compressor while running down the road. If my compressor has high duty cycle I know I have a leak even if I can't hear it.

If you can't see 3 psi on the gauges, go 2 min and look for a 6 psi drop, or 4 min for a12 psi drop. If you can't tell 12 psi difference on a gauge reading either you need new gauges or new eyes.

I will test it tomorrow and report back! 

[Joey Mack]

Ok.. im dropping out of this one.. sorry GW. I was just asking a simple question.  

[Geoff Weeks]

3 minutes ago, Joey Mack said:

Ok.. im dropping out of this one.. sorry GW. I was just asking a simple question.  

I wasn't criticizing your question, sorry if it came off that way I didn't mean it to. Please accept my apology. 

I was just saying, that high cut-out pressure wouldn't cause the problem he was having. 

He may have multiple problems, esp if the pressure is that high, but it wouldn't be the cause for this particular problem. 

Because of the lack of clarity from the O/P all the way through, I think focusing on one at a time. 

[70mackMB]

4 hours ago, nbone28 said:

I unhooked the emergency line from the trailer and hooked it up to my airline to air up the tires and had no problem with the button staying pushed in when hooked to that. I go back to hook it up to the trailer and it won’t stay pushed in. 

He posted this back in the middle of the 2nd page. Wouldn't this be the same as plugging off the red line using it as a tire inflater? Then it fails hooked to the trailer.    .....Hippy

[Geoff Weeks]

2 hours ago, 70mackMB said:

He posted this back in the middle of the 2nd page. Wouldn't this be the same as plugging off the red line using it as a tire inflater? Then it fails hooked to the trailer.    .....Hippy

The problem is: he doesn't know enough about air brakes to pass the pre-trip portion of the CDL test, there seams to be no way to get him to clearly answer or follow the directions.

Mecho in the 1st 2 replies was trying to get him to separate the truck from the trailer air system to see which it was in. It wasn't until much later on, that he did disconnect the trailer, by then we were well down the rabbit hole because he didn't do what was asked by the 1st guy who tried to help. I mistakenly assumed he had followed Mecho's advice and was digging deep into the truck system, when in fact he hadn't and so I sent him on a goose chase based on what he said, not what he did.

Yes, using an inflatetor hose (depending on length) is more or less plugging, but by that time the damage was done.

A person who doesn't even know the correct operating pressure of a trucks air system, should not pass a CDL test, never mind work on truck air brakes.

Ignorance is not a sin, everybody starts out not knowing stuff, however if you ask for help and are given clear instructions, either follow and report or admit you don't understand or know how to do what is asked.

The lack or clarity in his responses likely cost him the price of an MV-3 and the time it took to install.

Not knowing the working pressure of a truck air system or how to look for leaks (Something required in a pre-trip) is a clear indication that he shouldn't be working on the brake system without some qualified help right there with him.

It is no skin off my nose (or as we used to say in the repair shop "My truck works") but people can get hurt or killed if a defective vehicle is on the roads.

Again, everybody has to learn, but you have to be willing to admit your ignorance and ask questions if you don't understand what people like Mecho are asking him to do. Mecho's 1st post was to break the problem in half, the best and most basic diagnosing action. Ignoring it and not clearly saying he didn't do it, wasn't accepting help given freely. You can't learn if you are not open to it.

 

[nbone28]

8 hours ago, Geoff Weeks said:

The problem is: he doesn't know enough about air brakes to pass the pre-trip portion of the CDL test, there seams to be no way to get him to clearly answer or follow the directions.

Mecho in the 1st 2 replies was trying to get him to separate the truck from the trailer air system to see which it was in. It wasn't until much later on, that he did disconnect the trailer, by then we were well down the rabbit hole because he didn't do what was asked by the 1st guy who tried to help. I mistakenly assumed he had followed Mecho's advice and was digging deep into the truck system, when in fact he hadn't and so I sent him on a goose chase based on what he said, not what he did.

Yes, using an inflatetor hose (depending on length) is more or less plugging, but by that time the damage was done.

A person who doesn't even know the correct operating pressure of a trucks air system, should not pass a CDL test, never mind work on truck air brakes.

Ignorance is not a sin, everybody starts out not knowing stuff, however if you ask for help and are given clear instructions, either follow and report or admit you don't understand or know how to do what is asked.

The lack or clarity in his responses likely cost him the price of an MV-3 and the time it took to install.

Not knowing the working pressure of a truck air system or how to look for leaks (Something required in a pre-trip) is a clear indication that he shouldn't be working on the brake system without some qualified help right there with him.

It is no skin off my nose (or as we used to say in the repair shop "My truck works") but people can get hurt or killed if a defective vehicle is on the roads.

Again, everybody has to learn, but you have to be willing to admit your ignorance and ask questions if you don't understand what people like Mecho are asking him to do. Mecho's 1st post was to break the problem in half, the best and most basic diagnosing action. Ignoring it and not clearly saying he didn't do it, wasn't accepting help given freely. You can't learn if you are not open to it.

 

I had separated the trailer from the truck and tested it that way. From the initial posting I said when I go push in the trailer air supply that is when the leak is happening. I’d assume the trailer is the problem just from that. I’m answering all the questions that are being asked. The MV-3 was $200 and took about 5 mins to swap out. Not too worried about that. It looked like it needed to be replaced anyways. 

[Geoff Weeks]

14 hours ago, Geoff Weeks said:

Mecho told you on page one to block off the trailer lines, I assumed you had.

It is looking like the trailer is dumping all air (It isn't a belly dump with a huge air tank is it?)  If the trailer requires a full fill it can take a lot of air. 

You are moving too much air into the trailer line, more that the 3/8" line can supply at the volume needed to recharge the trailer. Once the pressure builds in the trailer, the volume decrease and the pressure at the valve rises above the tripper pressure. 

Important to follow all the points on suggested or VERY clearly state you did not.

 

14 hours ago, mechohaulic said:

you haven't separated the trailer from the tractor YET !!! take the red/ blue lines OFF the trailer and cap them. using a plugged glad hand or holder mounted on the pogo stick. THEN PUSH IN THE RED BUTTON TO SEE IF YELLOW LINE LEAKS . a faulty trailer valve /// brake can will return air to THE TRACTOR !!!!!

These were from page two, It wasn't clear to me or to Mecho that you had disconnected the trailer at that time. We are not mind readers.

 Your admission that you don't know what the system pressure in an air braked truck is, shows you need some guidance from someone looking over your shoulder until you learn the very basics of air brake systems.

Operating pressure and how to check for leaks that can't be heard are very basic skills needed to work on the system. They are also part of the pre-trip portion of the CDL test. 

[nbone28]

8 minutes ago, Geoff Weeks said:

 

These were from page two, It wasn't clear to me or to Mecho that you had disconnected the trailer at that time. We are not mind readers.

 Your admission that you don't know what the system pressure in an air braked truck is, shows you need some guidance from someone looking over your shoulder until you learn the very basics of air brake systems.

Operating pressure and how to check for leaks that can't be heard are very basic skills needed to work on the system. They are also part of the pre-trip portion of the CDL test. 

Okay so where do I start then?

[Geoff Weeks]

Ok, if I understand you correctly, the problem only shows when you are connected to the trailer. Please confirm this is so.

 If the above is true the trailer is the problem, not the tractor.

A trailer that completely bleeds off all stored air pressure so every tank in the trailer is at 0 psi, will require briefly holding in the red button when it is 1st charged until the supply line to the trailer reaches the "autotripper" pressure in the valve. This is normal operation. The valve is supposed to automatically pop out if the line pressure is below 25-40 PSI

 "why did this just start" you may ask? Well you have a leak in the trailer system that is bleeding off all the pressure. Normally it is common for a trailer to bleed down when parked, esp air ride trailers, but there is a valve that is supposed to cut the air to the air suspension and save the air pressure below about 55 psi for the brakes. 

So how do you determine if you have a big leak, by the DOT pressure test I wrote about earlier DOT pre trip says this is supposed to be done with the pre trip inspection, or by measureing the time it takes for the compressor to cycle back on (blow off to blow off time). I freely admit that I don't do the DOT pressure check on pre trip but rather assess the condition by the duty cycle of the compressor. They both are a measure of how much pressure leaks off in a given time. The DOT method is the one you may be tested against in a level 1 DOT inspection, my method is just a easy way for me to assess the condition of my air system while driving.

So called silent leaks can be hard to find, it takes going over everything with soapy water in a spray bottle, looking for bubbles. Sometimes a piece of hose held to your ear can mask surounding sounds and help narrow in on a leaky valve.

Braided covered rubber hose can leak along its length and not make a sound but will bubble the entire length when sprayed with soapy water.

[nbone28]

2 minutes ago, Geoff Weeks said:

Ok, if I understand you correctly, the problem only shows when you are connected to the trailer. Please confirm this is so.

 If the above is true the trailer is the problem, not the tractor.

A trailer that completely bleeds off all stored air pressure so every tank in the trailer is at 0 psi, will require briefly holding in the red button when it is 1st charged until the supply line to the trailer reaches the "autotripper" pressure in the valve. This is normal operation. The valve is supposed to automatically pop out if the line pressure is below 25-40 PSI

 "why did this just start" you may ask? Well you have a leak in the trailer system that is bleeding off all the pressure. Normally it is common for a trailer to bleed down when parked, esp air ride trailers, but there is a valve that is supposed to cut the air to the air suspension and save the air pressure below about 55 psi for the brakes. 

So how do you determine if you have a big leak, by the DOT pressure test I wrote about earlier DOT pre trip says this is supposed to be done with the pre trip inspection, or by measureing the time it takes for the compressor to cycle back on (blow off to blow off time). I freely admit that I don't do the DOT pressure check on pre trip but rather assess the condition by the duty cycle of the compressor. They both are a measure of how much pressure leaks off in a given time. The DOT method is the one you may be tested against in a level 1 DOT inspection, my method is just a easy way for me to assess the condition of my air system while driving.

So called silent leaks can be hard to find, it takes going over everything with soapy water in a spray bottle, looking for bubbles. Sometimes a piece of hose held to your ear can mask surounding sounds and help narrow in on a leaky valve.

Braided covered rubber hose can leak along its length and not make a sound but will bubble the entire length when sprayed with soapy water.

Yes the problem only occurs when I am connected to the trailer, disconnect the airlines from the trailer and no issue. There’s no issue with the truck. 

When I come in the next morning the air pressure is usually sitting at 55psi in the secondary tank and a bit more i’d say like 65-70psi in the primary tank. 

[Geoff Weeks]

Ok, truck is fine, problem is trailer is leaking off. 

Concentrate on the trailer. chock wheels, start truck allow to build pressure push in buttons a fully charge the trailer until the compressor shuts off (dryer vents) then turn off the engine without disturbing the buttons and watch the air gauges for the 3 psi/min max drop. If it is dropping fast it is a big leak and should be easy to find, if it is dropping slow it will take more work to find.

[nbone28]

15 hours ago, Joey Mack said:

If you have 160, you need to look at the pop off valve, and dial the governor down or replace it..  125-140 is good enough

It vents at 130psi

[nbone28]

1 hour ago, Geoff Weeks said:

Ok, truck is fine, problem is trailer is leaking off. 

Concentrate on the trailer. chock wheels, start truck allow to build pressure push in buttons a fully charge the trailer until the compressor shuts off (dryer vents) then turn off the engine without disturbing the buttons and watch the air gauges for the 3 psi/min max drop. If it is dropping fast it is a big leak and should be easy to find, if it is dropping slow it will take more work to find.

The problem is now the trailer air supply (red button) won’t stay pushed in. It just pops right back out. So I can’t even supply the trailer with air. 

Edited Friday at 03:40 PM by nbone28

[mechohaulic]

(1) is this the new valve assy you had put in ? (2) did you try with trailer lines disconnected ? (3) by chance red/blue lines not crossed = had to ask , 

[nbone28]

1 minute ago, mechohaulic said:

(1) is this the new valve assy you had put in ? (2) did you try with trailer lines disconnected ? (3) by chance red/blue lines not crossed = had to ask , 

yes this is the new valve assemble, lines are off button still won’t stay pushed in, the supply for the truck goes in and stays in perfectly fine. it’s the trailer one that won’t. No the lines aren’t crossed. 

[mechohaulic]

i'd go with a defective new valve.  if the swap isn't too major = do you still have old one ? knowing issue is trailer . put old valve back in to test possibility  of defective new part.

[mechohaulic]

you stated old valve was worn = but still usable enough to hook/ move trailer ; and have defective valve for return.

[nbone28]

2 minutes ago, mechohaulic said:

you stated old valve was worn = but still usable enough to hook/ move trailer ; and have defective valve for return.

 

[nbone28]

16 minutes ago, mechohaulic said:

you stated old valve was worn = but still usable enough to hook/ move trailer ; and have defective valve for return.

taking the new valve back, claim it’s faulty and swap it out 

[Geoff Weeks]

1 hour ago, nbone28 said:

yes this is the new valve assemble, lines are off 

Red button will not stay in if the red trailer line is open to air. You need to put a dummy gladhand on to test the tractor.

I think, according to what we have read, that it does eventually stay in when hooked to the trailer after holding in long enough to charge the trailer. This is normal, the tractor is not the problem.

In all my years on my own equipment I only changed one MV and that was because I couldn't get the gasket to repair the old MV-2 on the truck. They don't go bad that often. I since got a new gasket for the MV-2 and re installed it, kept the gaskets in stock because all 3 of my truck had the same valve (which was why I re-installed, the replacement was a Midland and the rest of the fleet was Bendix MV-2)