What I’m trying to clarify is that a true expansion tank with a bladder is needed in a sealed pressurized system to keep o2 out of the water. Even if water or air is pumped into a single chamber sealed tank only half full of either, the air will eventually dissolve into the water under pressure and the tank will in time become full of water leaving no room for further expansion. My point is that there needs to be a barrier between the air and water or it won’t work.
Since we’re talking sealed system, the remaining gasses have no where to go but stick around in the expansion tank. With a home water system (open system)new water is constantly passing by that can dissolve the remaining air. With a sealed boiler there is no where for the gasses to go. At higher temperatures gassse will actually come out of solution and be added to the expansion tank.
But most sealed systems have a low pressure reg. that is hooked to the potable water and have air traps to remove air that comes out of suspension when heated. My feel is that the air in the non bladder tank will always become entrained in the water and removed with the air trap until all the air is gone-thus no room for expansion.
Even if the system didn’t have a constant fill valve the air trap should be installed. The operator would be constantly adding water in response to the drop in pressure from the air being removed with the air trap.
But most sealed systems have a low pressure reg. that is hooked to the potable water and have air traps to remove air that comes out of suspension when heated. My feel is that the air in the non bladder tank will always become entrained in the water and removed with the air trap until all the air is gone-thus no room for expansion.
Even if the system didn’t have a constant fill valve the air trap should be installed. The operator would be constantly adding water in response to the drop in pressure from the air being removed with the air trap.
We obviously need someone with realife experience with such an animal to respond. My bet is that the losses would be very small and annual expansion tank draining would be plenty without too much oxygen added to worry about when you consider the amount of iron in the whole system.
It was Gary’s idea to use a propane tank as my expansion. He does it often and has rarely had a problem.
He claims it will work fine as long as the expansion tank is at end of line (single pipe) with no water flow passing.
A well tank for potable water has constant flow and therefore requires the bladder. This situation was not so complicated
when speaking with Gary. I trust him and will follow his advice
the expansion tank on the Switzer ,Ed and I looked at in Mansfield Ct. did have a bladder in Gary’s own manufactured expansion tank. as for the propane tank I have no idea.
The Mansfield boiler install is a typical one for Gary from what I understand. But he did suggest I go with the used propane tank. I will call Gary and a few local “old school” plumbers tomorrow to clarify this and report the results. I don’t want to make a mistake on 3k storage at 200* + temps.
Expansion tank clarification...............hopefully.
In a sealed and pressurized system one has to account for the expansion and contraction of the heated fluid be it straight water or a glycol mix. This is the sole purpose of an expansion tank. Not to capture and retain air that may be in the system piping. That air you definitely want to get out via the air scoop or air elimination device. In a captive air type tank (bladder or diaphragm) a cushion of air is maintained on one side of the membrane and system water is on the other side. These tanks can typically be of smaller volume than an “open” tank for a given total system volume.
Now...remember that the air or gas in an open style tank or compression tank if you will, consists of components other than oxygen, which is the stuff that causes corrosion. Once the oxygen is dissolved into the system and eliminated through your “air” elimination device you are left with a mostly benign mixture consisting of nitrogen and a few other inert gases.
In a captive air type tank or true expansion type tank, there is no direct interface between the system water and the air cushion. The system water can expand against the bladder or diaphragm and keep the system pressure where it should be. These tanks must be precharged to about 2PSI less than what the system will require for operation.
The bottom line in both cases, expansion or compression style tanks, is that their function is to maintain system pressure, not capture and/or eliminate air.
Expansion tank clarification...............hopefully.
In a sealed and pressurized system one has to account for the expansion and contraction of the heated fluid be it straight water or a glycol mix. This is the sole purpose of an expansion tank. Not to capture and retain air that may be in the system piping. That air you definitely want to get out via the air scoop or air elimination device. In a captive air type tank (bladder or diaphragm) a cushion of air is maintained on one side of the membrane and system water is on the other side. These tanks can typically be of smaller volume than an “open” tank for a given total system volume.
Now...remember that the air or gas in an open style tank or compression tank if you will, consists of components other than oxygen, which is the stuff that causes corrosion. Once the oxygen is dissolved into the system and eliminated through your “air” elimination device you are left with a mostly benign mixture consisting of nitrogen and a few other inert gases.
In a captive air type tank or true expansion type tank, there is no direct interface between the system water and the air cushion. The system water can expand against the bladder or diaphragm and keep the system pressure where it should be. These tanks must be precharged to about 2PSI less than what the system will require for operation.
The bottom line in both cases, expansion or compression style tanks, is that their function is to maintain system pressure, not capture and/or eliminate air.
Thanks Heaterman for the facts. I’m curious, would you use a expansion or compression in a large pressurized system?
Expansion tank clarification...............hopefully.
In a sealed and pressurized system one has to account for the expansion and contraction of the heated fluid be it straight water or a glycol mix. This is the sole purpose of an expansion tank. Not to capture and retain air that may be in the system piping. That air you definitely want to get out via the air scoop or air elimination device. In a captive air type tank (bladder or diaphragm) a cushion of air is maintained on one side of the membrane and system water is on the other side. These tanks can typically be of smaller volume than an “open” tank for a given total system volume.
Now...remember that the air or gas in an open style tank or compression tank if you will, consists of components other than oxygen, which is the stuff that causes corrosion. Once the oxygen is dissolved into the system and eliminated through your “air” elimination device you are left with a mostly benign mixture consisting of nitrogen and a few other inert gases.
In a captive air type tank or true expansion type tank, there is no direct interface between the system water and the air cushion. The system water can expand against the bladder or diaphragm and keep the system pressure where it should be. These tanks must be precharged to about 2PSI less than what the system will require for operation.
The bottom line in both cases, expansion or compression style tanks, is that their function is to maintain system pressure, not capture and/or eliminate air.
Thanks Heaterman for the facts. I’m curious, would you use a expansion or compression in a large pressurized system?
It would depend on the various factors of the installation. An expansion tank can be mounted anywhere. On the floor, hung from the ceiling, strapped to a wall sitting on a shelf plus they will service a larger volume of water for a given physical tank size. One would want to connect it to the system at the same location as the feed water pressure reducing valve.
A compression tank has to be mounted above the water level of the boiler for obvious reasons. Sometimes this works out really well and in many cases where we have installed a new boiler(s) in an existing system we re-use the compression tank if it’s in serviceable shape.
Then there are matters concerning ASME rating for commercial systems with large tanks (they are considered to be a pressure vessel also along with the boiler)......... So many factors, so little time.........
In most circumstances we will use an expansion style bladder or diaphragm tank.
Not needing an expansion tank or bladder of any kind is one of the nice features of a Garn.
Well, construction has started on my “Switzer Shed”. It’ll be 18’x24’ and will house a 1450 gal. Switzer boiler and anywhere from 3-6 full cords of wood. Things got rolling quicker than I was ready for, (contractor availability) so it’s been a whirlwind. We’re running Thermopex piping between the boiler and our house (75’) and my inlaw’s (220’). I’ll post pics as they become available. Right now, I’m waiting for the slab to be poured tomorrow, and my builders have constructed the walls already. I’m busy dropping trees w/ new leaves so they’ll dry for the next couple of months before I cut them and split them. Fun stuff!
My Switzer 3 pass 1050 w/ the two 1000 gal propane tanks was fired today for the first time. We raised the temp of all 3050 gal from 60* to 140* in just over 3 hours. Started the burn with two year seasoned splits and had no smoke out the chimney in less than 5 min. then added some two week old fresh cut and unsplit rounds to see what she could do… a little smoke and lowered stack temps but a suprisingly clean burn. Those green rounds hung around till the end even after we loaded more dry stuff an hour later so I will always try to avoid green wood. It’s not worth the lost BTU’s. The burn averaged @ 675,000 btu but when loaded with the dry stuff she chugged out over 850,000! IMHO the Garn is the next best thing, after a Switzer....
Next week I will try to get her up to 7 digits....
