Fld 120 air tanks/ problem

95 fld 120.

I'm trying to understand the air tanks on my truck and I'm also having a problem.

On the passenger side there is a small tank or wet tank, then I think it would be the primary tank and then the secondary tank is behind that.

On the driver's side there's another tank directly across from that secondary tank.

On the front part of that tank it has smaller Airlines coming out from like a manifold - it looks like it has some type of button that you can push on there- and also a large airline that runs toward the front of the truck.

On the back end of the tank there's another manifold I think with another button but just one small line comes out of it. There is another large airline that runs over to the secondary tank. I could not get any pictures because my phone crapped out, but I can get some tomorrow.

What is the name of that tank? What does it do? Does it fill only from the front or does the secondary tank fill it also? Or is it supposed to help fill the secondary tank? Where does that line go that runs from the front of that tank?

The problem I'm having is that I open the drain valve and it will forcefully spit out a white watery milky stuff, but then it sort of spits a little bit and just stops even though the truck has plenty of air.

I shut the drain valve off and I can hear the tank maybe every two or three seconds go- sh.. sh.. sh.. sh...

So to me, it sounds like the tank is restricted and not allowing air to just come in.

Are there check valves on that tank that could be having a problem? Some other problem?

 

That makes sense that the button regulates the pressure that the accessories work.

The truck has a new air dryer on it, but I still have not run the truck down the road yet. I drained all the other tanks and for some reason I didn't notice that tank or didn't think anything of it. The other tanks had the white milky crap too, but everything is clean now.

The other tanks expel air the way that they should. I will take the fitting off of the front of that tank and see if there is a check valve there to clean out. All of my airbags cab and suspension are new.

I am curious why that has an airline connected to the secondary tank, though.

And I'm curious where the line that comes out the front of the tank goes to.

 

So after receiving some good advice I did some testing.

Please refer to the photo below.

Under the truck on the passenger side is the wet tank, number one tank and number two tank.

On the driver side is number three tank.

I built the primary and secondary up to 120 lb. I drained tank number 2 and that drains everything from tank number one and from the wet tank.

The first of the two air gauges went to zero. The second gauge was still filled with air.

I then went into the cab and released the Maxi brakes. I stepped on the foot pedal and I can hear the air brakes exhausting air and I would lose air with each pump.

The diagrams online all show a wet tank and then a primary and a secondary. But this truck has a third tank on it.

Everything on the truck works the way that it should, yet tank number 3 won't drain properly, and as I listen I can hear air going shh... Shh... Shh every couple of seconds.

And tank number 2 and 3 are connected and number 3 is apparently fed from the front somewhere.

Has anyone seen a system like this before and can you explain it to me?

 

I only drained tank number 2. That seemed to drain tank number one and the wet tank.

There is no drain valve on tank number one only on the wet tank and on tank number 2. And tank number 3. I do not have two valves on any of the tanks.

When I get back at it again I'll check but I think you can drain the wet tank without losing air pressure.

 

It sounds to me the noise is the tank filling. Like it doesn't just fill it just gets a little bit at a time. Shh... Shh... Shh... every couple of seconds.

I can take the drain valve out and see if there's any problem with it, but it seems to me like the reason it won't expel the air properly is because it's having a hard time bringing it in.

I think that's the noise that I hear is the tank trying to fill.

Yet everything is working on the truck to the best of my knowledge.