Should i have a tank made?

That doesn't sound too bad for a price, especially since it is custom to your specs. See the simplest pressurized storage sticky for some details. Also do a thorough thread search as I know we have discussed this in depth on several occasions. I would say that you should put a DHW coil in as well. The baffle is a good idea to minimize mixing. Hopefully others will pipe in with answers to your fitting questions. I think 1.5" is pretty standard for heating systems though. Hot to top, cold from bottom. etc.

I will be building a pressurized tank soon. I have not decided on the materials yet, but I can tell you 1/4" carbon steel 4' x 8' sheet cost around $180 a piece. If I used 5 of them , I believe the tank would be just under 1000 gallons. So that alone is $900 not counting time, other material, welder, electricity, etc... sounds like your getting a good deal to me ...

If you are considering using flat plate steel even with baffles I would get a second opinion about the strength of a "box" tank for a pressure tank. Commercially I don't think you see square pressurized storage tanks. I looked into heavy gauge fuel storage tanks ( round body flat end ) and the manufacture said the round body of the tank would be OK but you would pop the ends out. Propane tanks = round bodies and domed ends. A box tank would be nice because on the same foot print you would get a lot more storage, but I don't think you can achieve the structural integrity needed for pressure vessel.
Rob

Rob's correct.

Rectangular pressure tanks are available. I probably would need to search awhile to find them. This is not the kind to have made though. Henfruit, is your tank going to be vertical? That price is very good if it includes the 4 weldelets(use 1 1/2"). My tank is 720 gallons(custom made) & with stainless 2 loop domestic coil $1700.00. Prices are very similar. $6.00 a roll fiberglass insulated my tank very well. Forget the baffles unless you think you will mix it up with excessive flow. My Laddomat charges perfectly. You can see my tank if you search Atmos boiler. I copied the fitting locations from various sources & this works very well. I think it is absolutly worth the money to have a tank built, Randy PS is this welder a commercial tank builder? There is special equipment to fit the heads right etc. At 20 psi the forces are a little scarry when you do the math.

RobC said:

If you are considering using flat plate steel even with baffles I would get a second opinion about the strength of a "box" tank for a pressure tank. Commercially I don't think you see square pressurized storage tanks. I looked into heavy gauge fuel storage tanks ( round body flat end ) and the manufacture said the round body of the tank would be OK but you would pop the ends out. Propane tanks = round bodies and domed ends. A box tank would be nice because on the same foot print you would get a lot more storage, but I don't think you can achieve the structural integrity needed for pressure vessel.
Rob

Click to expand...

http://www.newhorizoncorp.com/hotwaterstorage.php

If square was not okay, then all of our boilers would be round! Don't forget they are pressure vessels too...

My open tank has a dip tube at the top and bottom for charging and drawing. Instead of using a baffle to prevent mixing, I slowed the water down by running a pipe the length of the tank with small holes every few inches. That evenly distributes the flow. I would suggest having the small holes farther apart near where the pipe enters the tank and closer together toward the other end.

If square was not okay, then all of our boilers would be round!

Click to expand...

It's not that flat pressurized walls are bad design, it's just that they are much more expensive(lots more welding) and heavy by the time they are as strong as cylindrical and spherical tanks walls.

Tarm Solo 40 boilers have their largest sides built of steel about 5/16" thick. They drill holes on an 8" grid and weld rods through the two opposing holes in the inside and outside walls. These stays keep the walls from bulging out too much. Doing something like this for a large tank is going to be a lot of work and a lot of welds to make without leaks. Or you could get a pickup load of small I-beam and brace it on the outside like an insanely overbuilt concrete form. A spherical tank of the same volume as the Tarm would probably need more like 3/32" walls and much simpler butt welds to take the same pressure.

It's more economics than engineering that makes the vast majority of pressure vessels cylindrical.

Wood Not Oil. I didn't intend to disrespect any ones business. Those are nice tanks and commercially made. I stand corrected. And, as DaveBP pointed out you can get them or have them made. I had a 1000G "box tank" priced at $5 / gallon last summer from a local tank mfg. That's before insulation. There are also SOME plastics that will handle high temps that would allow you to do a NON pressurized set up and allow for higher temps than EDPM but you would need to reinforce the walls and insulate just like EDPM. Then the heat exchange set up, coils vs flat plate etc and more $$$.
Our wood boilers do hold gallons of pressurized water but no where near what a storage tank is being asked to because of the weight of the water alone. A Tarm 60 holds 60 gallons and weighs 1250 lbs. A 500G propane tank weighs about the same. Those are both dry weights.
If every thing works out $1500 sounds like a good deal.
850 G of near boiling water is no joke.
Again sorry Newhorizon....
Rob

Instead of baffle have him put in rows of ties to support the flat sides.

Make sure it can at least handle the pressure relief valve pressure which is normally 30 psi, but I would want it to handle the pressure of your fresh water system to handle the case when the tank is connected to the fresh water supply. Then test it with you and them there, you will sleep better and if they manufacture similar then they do the testing all the time.

You price looks really good.

RobC said:

Wood Not Oil. I didn't intend to disrespect any ones business. Those are nice tanks and commercially made. I stand corrected. And, as DaveBP pointed out you can get them or have them made. I had a 1000G "box tank" priced at $5 / gallon last summer from a local tank mfg. That's before insulation. There are also SOME plastics that will handle high temps that would allow you to do a NON pressurized set up and allow for higher temps than EDPM but you would need to reinforce the walls and insulate just like EDPM. Then the heat exchange set up, coils vs flat plate etc and more $$$.
Our wood boilers do hold gallons of pressurized water but no where near what a storage tank is being asked to because of the weight of the water alone. A Tarm 60 holds 60 gallons and weighs 1250 lbs. A 500G propane tank weighs about the same. Those are both dry weights.
If every thing works out $1500 sounds like a good deal.
850 G of near boiling water is no joke.
Again sorry Newhorizon....
Rob

Click to expand...

Actually Rob, it is rather counter-intuitive, but the strain on the walls of a pressure vessel has nothing to do with the amount of water in the vessel, and everything to do with the PRESSURE that the water is at... The wall of a Tarm at 20psi absolute is the same as that on the wall of a thousand gallon tank at 20psi absolute... It sort of makes sense if you think that in order for the vessel wall to have a different pressure, it would have to "know" what was exerting the pressure...

If I have 10 gallons of water and put it in a tank that was only a foot deep, the pressure on the tank wall would only be about 1/2 psi - I could just about make the tank walls out of plastic wrap - think a kid's wading pool... If I take the same 10 gallons of water, and put it in a really tall and skinny tank that was 33' tall, I'd have 15 psi on the tank wall at the bottom, and had better have some fairly substantial tank walls...

The problem with large non-round tanks isn't the volume of water, as such, rather it is the total amount of pressure exerted on the walls - even a few pounds per square inch add up to a lot of total pounds over several feet of surface area... As others have pointed out, when building a non-round vessel, it is often necessary to include "stays" in the tank construction to provide a counteracting tension to that outwards pressure - planning this takes some serious engineering, so I would share the concerns others have expressed about the "professional chops" of anyone building a DIY non-round tank because I want it to be done safely....

Gooserider

In addition to what everyone else has said - if you do a quick search on what it takes for fab shops to become ASME Pressure Vessel Welding certified you will quickly understand how complex this can be. Certified welders are a dime a dozen. ASME pressure vessel certified welders (and shops) are rather hard to come by.

If there are enough stays welded in the tank should be safe. When a pressure vessel fails(leaks) it is almost always at the stays. If you do have this built make sure they leave the stays hanging out a bit as in ASME specs. It may look a bit like a porcupine, it will much safer than flush weld stays. I toured the old ASME factory of Energy Mate & the engineers were not happy with the onsite ASME inspectors that made them start to weld in more stays as they often leaked first time around, Randy

If you do have this built make sure they leave the stays hanging out a bit as in ASME specs. It may look a bit like a porcupine, it will much safer than flush weld stays.

Click to expand...

This is how Tarm does it.

Myth Busters proved what 4 psi can do: http://www.youtube.com/watch?v=B8-JBgIlMyc

Squeezle Bob said:

Myth Busters proved what 4 psi can do: http://www.youtube.com/watch?v=B8-JBgIlMyc

Click to expand...

Absolutly; I started out going to use a 275 gallon oil tank & realized it would turn into a balloon with even mild pressures, Randy