need help figuring out how to re-route air supply lines

[jesusgatos]

OK, this might sound a little bit weird, but bear with me. I'm going to put the air tanks up on top of the cab (in a roof-rack). I need to be able to carry a lot of water and fuel in the M109 motorhome conversion that I'm building, and I figure that I can fit a 25-40 gallon tank where the air tanks were (depending on whether I remove the spare tire or not), so the air tanks gotta go. Better weight distribution.

So now what I need help with is figuring out the most efficient way to re-route the air supply lines. I've drawn a napkin-sketch to illustrate what I've got in mind (link to schematic), and would appreciate it if some of you that are more knowledgeable about the air systems on these trucks would take a look and give me some feedback. I've got to get this finished by Friday, so I'd like to go buy parts ASAP.


specific questions:

Can I just install a manifold somewhere between the compressor and the back of the cab, then plumb all of the air supply lines into the manifold and run one line up the back of the cab to the air tanks. The air pressure should be equalized throughout the system, right? So if that will work, is one 1/2" hose big enough?

What about the 3/8" air-line that went from the tanks to the thingamagig on the firewall that sends air to the air pressure gauge? I don't even know what that is, but can I tap that into the manifold as well, or does it need to read pressure AT the tanks? I wouldn't guess so, but I don't know much (anything at all) about the air systems in HD trucks.

What's up with the 3/8" air-line that runs from the airpack to a T-junction at the slobber-tube? I'm a little bit confused by that.

 

[Chevytruck]

how about just extending the existing airlines to the roof?

 

[Floridianson]

3/8 t slober on mine I left off at the air pack as I do not see my self with water that high ever. ( I stay out of the water cause it can cost alot in fluids when you milk) When you let off the pedal the air that is released goes through the tube and vents at slober. The new thing is also to seperate that line from the tee as it shares with fuel tank vent.
You will neeed a manifold drain and put in a air drier between comp and manifold. Your drawing will work, if you like it do it. It's just supply and demand.

 

[kaiser2help]

You may see some small fluctuation with regards to your air governor. But not enough to be an issue.

 

[m109guy]

I fitted two 42 gallon waste water tanks under the M109 without moving anything. There is tons of room under there. No need to move the air tanks.

But if you still want to move them, depending on your design, then I don't see an issue. Just move the tanks to the new location then run the new lines down to where the old lines went into the tanks before. Sounds like a pretty straight forward job.

 

[Boatcarpenter]

I think Chevytruck has the right idea. Move the tanks to the roof and just run lines from there to where you disconnected the others from the tanks.
BC

 

[gimpyrobb]

Don't forget to add a drain from your tanks. The water that comes out when you drain them is rusty and nasty. You will not want that touching your truck.

 

[jesusgatos]

how about just extending the existing airlines to the roof?

Well I could, but I'd have to run a lot more lines up/down the back of the cab if I did it that way.

3/8 t slober on mine I left off at the air pack as I do not see my self with water that high ever. ( I stay out of the water cause it can cost alot in fluids when you milk) When you let off the pedal the air that is released goes through the tube and vents at slober. The new thing is also to seperate that line from the tee as it shares with fuel tank vent.
You will neeed a manifold drain and put in a air drier between comp and manifold. Your drawing will work, if you like it do it. It's just supply and demand.

Oh, so that line that goes from the air-pack to the slobber-tube is just a vent-line for the air-pack? That's good to know. I want to get a handle on what everything on this truck does, and how it all works.

You may see some small fluctuation with regards to your air governor. But not enough to be an issue.

Can you please tell me a little bit more about this? Is the air governor like a pressure cut-off switch or unloader valve? What activates that? I mean, where does it get it's pressure signal from? The main air-line where it leaves the compressor? Or is there another smaller air-line that I missed?

I fitted two 42 gallon waste water tanks under the M109 without moving anything. There is tons of room under there. No need to move the air tanks.

But if you still want to move them, depending on your design, then I don't see an issue. Just move the tanks to the new location then run the new lines down to where the old lines went into the tanks before. Sounds like a pretty straight forward job.

I am guessing that you put those tanks between the framerails? I can't do that on this truck because I installed a 10ft slide-out boarding ramp (from a uhaul truck) between the framerails. By the way, it fits PERFECTLY. I'll start another thread and post some pics.

I know it's a pretty simple project, but I don't want to overlook anything important and I'm not familiar with any of the components in this system, so better to ask questions now than make a stupid mistake that could have serious consequences if something went wrong. Right?

I think Chevytruck has the right idea. Move the tanks to the roof and just run lines from there to where you disconnected the others from the tanks.
BC

Basically, yeah. But I want to add a manifold so that I can cut down the number of lines that I have to run up the back of the cab.

Don't forget to add a drain from your tanks. The water that comes out when you drain them is rusty and nasty. You will not want that touching your truck.

Thanks. There are drains in the diagram, but I went to a local HD truck shop/parts store this afternoon and I got some really good advise. Here's what I found out:

They didn't see any problems with my basic plan/layout, but they did suggest that I run two lines up to the tanks. They said that I should run one line straight from the compressor up to one of the tanks, and then run another line from the other tank back down to the manifold. The reason they said I should do it that way is because the 1st tank will capture most of the condensation as the incoming air cools down. They called it the 'wet tank'. The 2nd tank is the 'dry tank', and doesn't collect nearly as much moisture. So there will be two lines running up the back of the cab.

Well, three if you count the drain-line. I'm going to Tee those together and run one drain line down the cab and dump it somewhere under the truck. They have a few different options for drain valves, including some really trick cable-operated ones.

They told me that if there's not a check-valve on the compressor, that I should add one somewhere before the manifold. Is there a check-valve on the compressor? I didn't know.

They also suggested adding another drain-valve somewhere near the low-point in the system in case the air-pressure doesn't push all the moisture up to the tanks on top of the cab.

We talked about adding a simple water separator too. Not sure if that's something I'm going to worry about right now.


more questions:

What size air-lines should I run from the tanks to the quick-release fittings that I'll use to run air-tools? Is 1/2" OD big enough or should I go bigger?

What's that thing on the firewall that has a 3/8" air-line running to it from the air-tank? It's basically inline between the air-tank and the air-pressure gauge in the cab.


I'm going to go buy parts tomorrow and put it all back together. Well, sort of. I don't have a hard-top yet, so I can't build a roof rack, so I can't mount the air tanks. I'm just going to put them in the cab, under the passenger's seat for now, but all the hard work will be done and they'll be easy to move once I get the rack built.

 

[gimpyrobb]

Should be a check valve by the tanks in the stock setup. Can't remember where though. Have you priced them? OUCH! Not cheap.

 

[jesusgatos]

I didn't see a check valve anywhere. The only thing mounted to/on the tanks is a pressure blow-off valve. Where would the check valve be and what does it look like, because unless I've missed it - I don't think there is one on my truck.

 

[Bad_Carp]

I fitted two 42 gallon waste water tanks under the M109 without moving anything. There is tons of room under there. No need to move the air tanks.

Any photos of how and where you mounted the waste tanks?

 

[tm america]

m109guy where did you get your waste tanks and what arfe the deminsions of them

 

[jesusgatos]

He's got a couple of build-threads on that 109. Here's a link, but I don't think there's any specific info about those tanks.

 

[Bad_Carp]

He's got a couple of build-threads on that 109. Here's a link, but I don't think there's any specific info about those tanks.

Yea, I've gone through his build page about 150 times...he's done a fantastic job on his 109, but there were no details or photos of the mounted waste tanks (can't expect to show everything or it would be a novel).

 

[nk14zp]

Put the water tank on the roof and have gravity feed.

 

[jesusgatos]

Uh... no.

 

[nk14zp]

Why not?

 

[jesusgatos]

Weight distribution.

 

[nk14zp]

It aint a race car.

 

[jesusgatos]

Racecars are built to excel at whatever type of racing they were built for. I'm building an off-road oriented motorhome and it's not in my nature to do anything half-assed. What you're suggesting is just a BAD IDEA. Sorry dude, not gonna happen.