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Old 01-31-2008, 08:04 PM   #1
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Create extra space for holding tanks??

My model year did not come with a factory original grey water tank. I have been thinking about where to add new holding tanks on my 1973 31' Airstream. Also the black water tank was originally above the floor. Since I am doing a complete renovation I am pretty much free to put my holding tanks anywhere that makes sense. I was intially concerned that the frame is only about 5" tall and that it would be impossible to find a holding tank that would fit in that height and still have enough capacity if I also needed to stay between the stock cross-members. The first thought that I had a while back now was that it probably would be OK to hang down some as long as I did not hang below the bottom of the axles since that, after all, is what has to clear things in the road way. Recently it further occurred to me that I might be able to take some creative advantage of the fact that my axles are indeed lower than the rest of the belly pan. It also occurred to me that even though the bottom of an Airstream is generally aerodynamic that the axles themselves were not.

So here is what I am thinking that I will do:
  1. Install my tanks in the areas directly adjacent to the axles allowing them to hang down as far as the bottom of the axles.
  2. Add a lower belly pan that was just below the axles that would cover the bottom of the new tanks and streamline the axles themselves.
Since most of the area that is involved is within the range of the wheel wells there would be no need to make the new area any wider than the area in the wheel wells. The attached diagram shows the possible tank locations and notes that I would have almost 10" of tank height to work with.

Comments would be appreciated and I would be more than happy to offer further information if what I am proposing does not seem clear.

Malcolm
Attached Files
File Type: pdf LowerBellyPan.pdf (8.5 KB, 601 views)
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Old 01-31-2008, 08:37 PM   #2
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Just a few questions to better understand what your plan is...

What are the three tanks in the diagram?
Are you relocating the black tank?
What will your new capacities be?
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Old 01-31-2008, 08:58 PM   #3
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Hi Malcolm! I haven't caught any of your posts in a while, glad to see you're still plugging along on the project!
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Old 01-31-2008, 09:14 PM   #4
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Malcolm,

This looks good. It's very much like the 17' Boler we had before the Airstream. In that situation the tanks were about 2 inches higher than the bottom of the axle, and there was no tank above the axle but in front of it (the shallower one as you've shown). There was no bellypan on those trailers but most people ended up putting a board down in front of the front tank to protect it from road debris kicked up by the TV and those boards took a beating. I'd be prone to using something with more strength than aluminum for the lower belly pan, but otherwise I think you have a good model. This what our friends redoing their 52 and 53 Flying Clouds are intending to do as well given one of them still owns his Boler.

Keep us posted as you do this and once they get started we'll do the same.

Thanks,
Barry
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Old 01-31-2008, 11:07 PM   #5
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Quote:
Originally Posted by malconium
My model year did not come with a factory original grey water tank. I have been thinking about where to add new holding tanks on my 1973 31' Airstream. Also the black water tank was originally above the floor. Since I am doing a complete renovation I am pretty much free to put my holding tanks anywhere that makes sense. I was intially concerned that the frame is only about 5" tall and that it would be impossible to find a holding tank that would fit in that height and still have enough capacity if I also needed to stay between the stock cross-members. The first thought that I had a while back now was that it probably would be OK to hang down some as long as I did not hang below the bottom of the axles since that, after all, is what has to clear things in the road way. Recently it further occurred to me that I might be able to take some creative advantage of the fact that my axles are indeed lower than the rest of the belly pan. It also occurred to me that even though the bottom of an Airstream is generally aerodynamic that the axles themselves were not.

So here is what I am thinking that I will do:
  1. Install my tanks in the areas directly adjacent to the axles allowing them to hang down as far as the bottom of the axles.
  2. Add a lower belly pan that was just below the axles that would cover the bottom of the new tanks and streamline the axles themselves.
Since most of the area that is involved is within the range of the wheel wells there would be no need to make the new area any wider than the area in the wheel wells. The attached diagram shows the possible tank locations and notes that I would have almost 10" of tank height to work with.

Comments would be appreciated and I would be more than happy to offer further information if what I am proposing does not seem clear.

Malcolm
Malcolm,

Keep in mind that tanks and the associated plumbing need access from time to time. Going directly above or between the axles complicates that fact.
Maybe a visit to the Airstream dealer would give you new ideas. The holding tanks on the new models protrude drastically down from the axle level, and so far there are little to no reports of trouble from that particular installation.
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Old 02-01-2008, 08:00 AM   #6
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Malcolm,

I'd put about 3/4" to 1" of polyisocyanurate insulation board between the belly pan and the tanks.
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Old 02-01-2008, 08:08 AM   #7
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I looked at an arangment like that for my 71 GT gray water tanks also. I finally decided not to because I didn't want my plumbing exposed like the new Airstreams. The only problem I am going to have is I can't find thin enough tanks to fit between the frame rails. If my calcuations are correct, and I use two tanks ganged together I should get a capacity around 35 gals. One tank above the single axle and one aft of it. I just need to pull the trigger on custom tanks.
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Old 02-01-2008, 08:28 AM   #8
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here is my new grey/ gray tank. It is right behind the axles and will be covered with an aluminum cover. Where it is, is not very noticeable at all. You actually have to look for it. It is 30 gallons and will have a 3" gate valve. I am also planning on fabricating some aluminum mud flaps to keep road debris from being shot up.
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Old 02-01-2008, 11:11 AM   #9
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Malcolm,

You're going to run into a few problems with your set-up, but the idea of keeping the tanks close to the axles is a good one. One problem is with tank 3, as Frank alluded to... if you needed to remove that tank, the only way to do so is to either remove the floor above or cut out one of the crossmembers. Problem number two is I think you are going to find you will have trouble plumbing the drains. They need to drain at the lowest part of the tanks which means you will need to run through the axles, which obviously is not possible.
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Old 02-01-2008, 11:56 AM   #10
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Response to questions and comments...

First of all I am not likely to use all three locations for holding tanks. I just wanted to show the range of possibilities. The location just behind the second axle (on the left in my drawing) is the most likely candidate. I have to look at available tank options again but I think I can get a tank in the range of 35 to 40 gallons to fit in that space. I have been contemplating using a combined black and grey water tank and the various issues with that have been discussed elsewhere in these forums. If I decide to go with a separate black water tank it would not need to be anywhere as near as big as the grey water tank.

As far as the plumbing beneath the tanks is concerned I have been thinking right along of installing a macerator pump for emptying my tank (or tanks). The ones that I have looked at are generally less than 4" in diameter and could easily fit in the space beneath the frame and above the new lower belly pan. There is about 2" of clearance between the top of the axles and the bottom of the frame. I could put a macerator pump at the end of tank 1 and connect to a 3" drain on that tank. If I use the other tank locations I could connect to them with a 1-1/2" to 2" drain. If I understand correctly the important thing with a macerator is that the pickup point on the tank needs to be at or near the bottom of the tank. The pump would be capabable of pumping over the axle - especially if the tanks in location 2 or 3 were just grey water. I could also envision using a seperate water pump to move grey water from the front tanks to the rear tank if I needed to. It would also be my plan to put a separate cutoff valve at the output of each tank so I could select which tank to drain. I would hope to be able to get valves with a remote cable connection so I would not have to crawl under the trailer to control them.

As far as access to the tanks for removal or repair is concerned I am not too worried about that. I would have to drop the new belly pan to gain access of course. I think that the tanks in position 1 and 2 could be dropped without removing an axle. If I did use location 3 the absolute worst case is that I would have to drop the front axle to get it out. I currently have my old axles off and my new ones still un-installed. If I remember correctly it might have taken me as much as 1/2 an hour to drop an axle for the first time. It is not really too big of a deal. Tank location 3 is the least likely to be used by me as well. How often am I going to have to drop a tank anyway?

I like the idea of putting a layer of foam insulation below the tank(s) and on the sides as well for that matter. On another note it is my understanding that modern holding tanks can be mounted with straps rather than having to be entirely supported from below. That is how I have contemplated mounting mine.

Malcolm
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Old 02-01-2008, 11:59 AM   #11
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Quote:
Originally Posted by 62overlander
Attachment 53525
here is my new grey/ gray tank. It is right behind the axles and will be covered with an aluminum cover. Where it is, is not very noticeable at all. You actually have to look for it. It is 30 gallons and will have a 3" gate valve. I am also planning on fabricating some aluminum mud flaps to keep road debris from being shot up.
Is your tank running from side to side or lengthwise? It is a little hard to tell from the picture.

Malcolm
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Old 02-01-2008, 12:01 PM   #12
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Quote:
Originally Posted by Aerowood
I looked at an arangment like that for my 71 GT gray water tanks also. I finally decided not to because I didn't want my plumbing exposed like the new Airstreams. The only problem I am going to have is I can't find thin enough tanks to fit between the frame rails. If my calcuations are correct, and I use two tanks ganged together I should get a capacity around 35 gals. One tank above the single axle and one aft of it. I just need to pull the trigger on custom tanks.
None of my plumbing will be exposed. As I mentioned above the macerator and associated draing plumbing will be entirely above my new lower belly pan. I would think you would like the idea of decreasing the drag caused by your axles hanging down too.

Malcolm
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Old 02-01-2008, 12:21 PM   #13
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Quote:
Originally Posted by malconium
Is your tank running from side to side or lengthwise? It is a little hard to tell from the picture.

Malcolm
Side to side.
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Old 02-01-2008, 12:31 PM   #14
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Malcolm, what side is your valve - street or curb side? Just wondering. I prefer it out the street side or the back to keep it away from where we are sitting under the awning (in case there's ever a leak), and also because most of the dump stations I've been to are set up for dumping on the street side.

I like what you are doing overall. I may reconsider how I have mine now which are inside the trailer. It would not take a lot of effort to move them below the floor. Keep the pictures coming please.

Thanks,
Barry
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