non pressurized tanks

[Karl_northwind]

so I have been looking for options other than the usual (buying or building a non-pressurized tank with lotsa copper in it) used/refurbished LP tanks, or something else. what I've come across is steel fuel/other liquid tanks like these:
http://www.turnertanks.com/Horizontal.html
stood on end, these would be awesome and cheap buffer tanks. We have to install as non-pressurized here, so I plan on doing a euro-closed system with expansion vessel connected to air scoop/top of tank.

can anyone come up with a reason not to do this? we can certainly treat the water if needed, but the internals of the boilers are bare steel if I recall correctly. some o2 scavenging chemicals are certainly cheap if they're needed.

we could certainly use a double wall tank if it's wise.

cheers,
karl

 

[hobbyheater]

stood on end, these would be awesome and cheap buffer tanks. We have to install as non-pressurized here, so I plan on doing a euro-closed system with expansion vessel connected to air scoop/top of tank.

Not really sure what the "air scoop/top of tank" is?

If it is a vented expansion above the proposed non-pressurized storage, my only concern would be what the static pressure created from the vented expansion tank could have on the non-pressurized storage tank.

I run 1000 gallons of unpressurized storage with a vented 40 gallon expansion tank on the floor above the boiler and storage. This 12 to 16 feet of head gives about 3 to 3 1/2 PSI at the boiler.

Pictured is the side of the storage tank on concrete saddles above the boiler.

 

[PassionForFire&Water]

As HobbyHeater pointed out the static head would be an issue.
If you look at the different type of tanks on their website, the thickness is related to the diameter of the tank, but they only need this increased thickness so the flat head doesn't deform.
If you put these tanks in the upright position then the bottom flat head will deform and also the welds will see tensions they are not designed for and possibility for leaks whit temeprature swings.
You realy need a dished head for anything that has some pressure in it.
If you like to get more technical information/formulas Google "Unstayed Flat Head".

The double wall tanks just have a small cavity so a leak detection system can be installed.
Typically these are used for oil/diesel storage where a leak detection sytem is required.

Also, these diameters will be difficult to get into an existing basement once you get over 500 gallons

Just out of curiosity, do you have any pricing on these type of tanks.
For a shop that is setup to build these tanks, it does not matter much if it is a flat or a dished head.
The cost of the steel (size of tank) will be the biggest factor.
Price goes up 4x if it's ASME U-stamp. That's a given.
After all the insurance companies and AIA-inspectors need to eat too.

 

[Karl_northwind]

I plan on very little static head. expansion vessel right on top of the tank. I'll be having something similar built locally, so I can make little tweaks and come up with the proper tank for the job.

the connection to the expansion vessel will be to the top of an air scoop in the primary loop (think where the air vent would usually go), and another from the top of the storage tank as a place to vent air out.

 

[Bob Rohr]

I plan on very little static head. expansion vessel right on top of the tank. I'll be having something similar built locally, so I can make little tweaks and come up with the proper tank for the job.

the connection to the expansion vessel will be to the top of an air scoop in the primary loop (think where the air vent would usually go), and another from the top of the storage tank as a place to vent air out.

Ideally you want 5 psi at the highest point in the system. If you have a multi story home, with baseboard or an air coil at the upper level, you want/ need 5 psi at that point to be able to move air out of the high point.

So from that highest point calculate what the pressure would be at the tank location.

Circ pumps like to have some positive pressure also. The hotter the fluid the more pressure is required to prevent cavitation in the pump. Pump manufacturers show the NPSH charts in their tech info.

Sure it could be done, it seems to be a middle ground between 15 psi pressurized system/ tank and open systems like OWF.

I'd buy a good quality 3- 5 psi, high flow, relief valve and mount it in the tank as an additional level of protection.

There are some tank manufacturers that build 75 psi, non listed tanks, or 150 psi tanks like air compressor tanks these tend to be much less $$ than the 300 psi ASME listed tanks, like LP tanks.

 

[Karl_northwind]

this system is being installed to replace an OWF non pressurized. seems like it'd be easy enough if the system was already operating open/no pressure.

the typical, basement infloor, DHW sidearm tube in tube and air coil in the furnace system. I have looked into air reciever tanks, and will use that if I need the pressure capacity.

 

[hobbyheater]

this system is being installed to replace an OWF non pressurized. seems like it'd be easy enough if the system was already operating open/no pressure.

the typical, basement infloor, DHW sidearm tube in tube and air coil in the furnace system. I have looked into air reciever tanks, and will use that if I need the pressure capacity.

In my system with storage only having static pressure, I have two coils inside the storage tank. One is for DHW and the second one is for running pressure to the zones. This set up has operated trouble free for over 30 years.