questions about building a pressurized system

[jwise87]

My experience has been with a standard open owb. It was homemade and it evaporated a lot of water. I added 5 gallons every 3 days. This build I would like to do it differently. Mine is a tank in tank design that I am pressure testing with 125 psi compressed air, so I am not concerned about it exploding. It will run into the house circulate through an air to water hx and come back. If it works like my last one did I will run water somewhere between 145* and 175*, I am not trying to run steam.

My question is what do I need in the circuit. Here is what I know I need. A 30 psi pop off valve, an expansion tank, and some kind of air scoop, as well as a fitting to add water to the system. Am I missing anything?

I am going to use a non diaphragm style expansion tank 10% the size of my system. Do I need to run the air that comes from the scoop to top of the expansion tank?

One more question. If I read other posts on here correctly I could run a pressurized system that was "open" if I can get a reservoir tank somewhere in the system high enough?

 

[warno]

I personally would never build a pressurized boiler without proper pressure testing and a proper stamp. For shear liabilty reasons. What if you overlook something and it fails. I know your tanks can take the pressure but what about the flat plate on the front of your boiler? Pressure is a flat plates worst enemy. It doesn't take much pressure to bow a flat price of steel without reinforcing.

Question for you, how was your old boiler vented? Was it a simple vent line out the top? I ask because mine is vented and it hasn't lost a noticeable drop of water in 2 years. Because the way i vented it.

 

[maple1]

Evaporating 5 gallons in 3 days would seem to indicate that if you build the new one more or less the same way you would stand a good chance of steaming & overpressurizing - something seems off there.

EDIT: What are you hoping to gain by pressurizing? You could add a higher open expansion tank to an open boiler to increase circ inlet pressures.

 

[salecker]

Hi jwise87
When you test your boiler to 125 psi,fill it with water first.Then add the air to the pressure you want.
If you suffer a catastrophic failure at that pressure with just air you will have a shrapnel bomb that you are next to.
With it full of water it can fail but there will be no flying shards of metal like if it explodes with air in it.
I tested all my cast iron rads to 80 - 90 psi full of water.

 

[warno]

Hi jwise87
When you test your boiler to 125 psi,fill it with water first.Then add the air to the pressure you want.
If you suffer a catastrophic failure at that pressure with just air you will have a shrapnel bomb that you are next to.
With it full of water it can fail but there will be no flying shards of metal like if it explodes with air in it.
I tested all my cast iron rads to 80 - 90 psi full of water.

Yes do this if you plan on pressure testing. This is called hydro testing.


Think about a pot of water boiling on a stove top with a vented lid on that pot. What do you see escaping from that vent hole? Steam. What is steam, evaporated water. Your boiler water will simply steam it's way right out of a top vented water jacket.

Look at how a garn boiler is vented. There's a vent line that runs up into the man way opening then down towards the bottom. This is how my boiler is vented because I copied that idea. In theory the evaporated water raises up to the cover then condenses into liquid and drops back into the water jacket. The stand pipe basically becomes an overflow pipe for pressure alone and boiled over water.

Here is a view in a garn. You can see the pipe going into the man way and out the front. That's the vent.

And my boiler. You can see the raised section of the water jacket, "the bubble". And you can see the stand pipe in the bubble that exits the bottom.

Here's the vent line that drops to the floor then exits the boiler shed.

 

[jwise87]

@warno so if I understand you the vent line sits in an air bubble at the top of your man way, and the man way has a lid so the water has to go out only that pipe. That makes sense and I am not far enough into my build that I can't add that. Thank you for the advice

The reason that I wanted it pressurized, and really I wanted it sealed more than pressurized, because what I read it will be more efficient and the system and the pump will last longer because I will have less O2. Heck if I run no pressure at all but have limited O2 exposure that would be great.

 

[maple1]

I would then avoid pressurizing it at all - but seal the boiler itself and pipe it to an open expansion tank up higher. So it is in effect an open boiler, but there will be static pressure at the circs from the water height (0.4psi/foot). I would still put a pressure relief valve on the boiler, just in case. And the connection to the tank should have no valves in between - so no chance of a valve being accidentally closed and turning it into a pressurized boiler.

My boiler is pressurized, but the install instructions also have a diagram for doing it this way, with an open expansion tank up high. Apparently it must be common for it to be done that way in Europe, where it came from.

There is also one OWB company that uses or used a tire tube kind of thing at the top of it, for the same reasons (less oxygen). I forget who though.

 

[jwise87]

I would then avoid pressurizing it at all - but seal the boiler itself and pipe it to an open expansion tank up higher. So it is in effect an open boiler, but there will be static pressure at the circs from the water height (0.4psi/foot). I would still put a pressure relief valve on the boiler, just in case. And the connection to the tank should have no valves in between - so no chance of a valve being accidentally closed and turning it into a pressurized boiler.

My boiler is pressurized, but the install instructions also have a diagram for doing it this way, with an open expansion tank up high. Apparently it must be common for it to be done that way in Europe, where it came from.

There is also one OWB company that uses or used a tire tube kind of thing at the top of it, for the same reasons (less oxygen). I forget who though.

I suppose it I had a tank up high might be almost as good, because I don't think it would get much circulation up there so that shouldn't introduce a lot of O2.

 

[maple1]

Warnos setup sounds like it's working pretty good to though. If it is just O2 or evaporation you want to address, the extra tank may or may not be worth it. If you want a bit more head at your circ inlets, the tank may be the way to go. if not, might be simpler to do the bubble & stand pipe type thing. 6 of one....

 

[jwise87]

Thanks everybody for your concerns, and thank you even more for the alternative ideas. I'll either go with the higher expansion tank or with the stand pipe depending on if I can find a man door.

 

[warno]

My man way is nothing more then a 1/4" plate I cut a square hole in and drilled a bolt pattern in.

You can see the bolt holes in the picture above and here's my cover. I simply use a rubber gasket material to seal it.

 

[Rick18]

Thats a nice looking job your doing on the boiler, I wish I could weld like that. I like the closed systems, there more money at the beginning but they last a long time. A friend of mine has a closed out door boiler and he has his set up like my indoor wood boilers running directly into the oil boiler and he has never had an issue.

 

[Buzz Saw]

I have a Garn WHS2000. This is my second season and I have not had to add any water to the system.

One thing Garn (I'm sure others do too)does to combat O2 is cleaning/preping the system which "seasons" the metal kind of like a cast iron skillet. After running tgmhe prep and flushing the system an anti-corrsion oxygen scavenger chemical is added to the water.
I send out a water sample about ever 6 months. They tell me what and how much chemical to add.

Sent from my SM-G950U using Tapatalk

 

[jwise87]

I have a Garn WHS2000. This is my second season and I have not had to add any water to the system.

One thing Garn (I'm sure others do too)does to combat O2 is cleaning/preping the system which "seasons" the metal kind of like a cast iron skillet. After running tgmhe prep and flushing the system an anti-corrsion oxygen scavenger chemical is added to the water.
I send out a water sample about ever 6 months. They tell me what and how much chemical to add.

Sent from my SM-G950U using Tapatalk

After a little more research on my current build I think I must have had hot spots in my first owb that were boiling off the water. I also had a large open reservoir it could evaporate off of. The chemicals are probably a good idea as well. I didn't run any in my last boiler.