Expansion Tank Orientation

ccstelmo

I couldn't reach the local page on this so I've got to bother you guys about it.

It's always amused me when I walk into a boiler room and see an Extrol tank with the lettering upside down. But now I'm a little humbled because in this boiler room the Extrol tank confuses me. I have not been there and don 't intend on going there because it's in Lexington Kentucky and I'm in Colorado. But the building superintendent is a buddy and asked me about some symptoms and sent pictures.

It's a 750Kbtu boiler serving two huge fan coils that are also right there in the mechanical room. They are the only load. A very large air seperator with a B&G vent on top and a tap for a nearby (and physically higher) ASME rated Extrol tank is on the suction side of the pump. Each fan coil has its own air vent (Hoffman) on the return side of its' piping. There is no automatic feed valve.

The original complaint was that the boiler needed continual refilling and the gauge responded instantly to his doing so. I told him his expansion tank was water logged and he had a leak somewhere. He found the leak in a failed Hoffman air vent associated with one of the fan coils and replaced the air vent. During that process he checked the air charge on the tank and it was 1 psi. He charged it to 15 psi but on further examination discovered there was no water at all on the water side of the bladder. In other words, both sides of the bladder had air.

The tank is oblong but is mounted vertically near the ceiling.. The air valve is on the high end at the ceiling and the boiler connection is on the low end. There is no mounting "base" or "stand" on either end. The writing on the tank is oriented along the long axis and so one has to turn ones' head sidewise to read it. I told him the tank was mounted upside down and too high and that he needed to move it to floor level, turn it so the air valve was on the bottom and the boiler connection was on top and reconnect it to the boiler. allowing boiler fluid to enter the tank.

But then I got to thinking and told him to hold off until I talked to you guys ……

What bothers me is the lettering on the tank.

If I were in the business of fabricating tanks I would definitely put my name on it so it could be read without standing on ones head or turning ones head sidewise. BUT IF THE TANK IS OBLONG, AND THE WATER INLET IS CENTERED ON THE TANK, HOW DOES THE WATER SIDE OF THE BLADDER GET FULLY PURGED OF AIR? I mean, during the filling process air WILL be trapped above the level of the water inlet of the tank on the wrong side of the bladder!

I'll quit now and let you guys think this over. Sorry to be so wordy but I'm trying to be precise and give you an accurate picture. (And the picture below should help)

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Jamie Hall

They can be mounted either way up. If the tank is precharged correctly, there will be little or no air on the water side of the tank, no matter which way up it is oriented.

EBEBRATT-Ed

What @Jamie said.

Although the orientation may not be right the tank will work no matter where it is mounted.

ccstelmo

Sorry, I'm still not getting it.

I. Both sides of the bladder were bone dry indicating there was a HUGE volumn of air in the tank.

2. When the operator attempted to put water in the system the gauge wanted to immediately peg, implying there was a HUGE vollumn of water in the tank. (WATER LOGGED Tank.)

3. These symptoms are contradictory.

4. If you can orient it any way you want and you orient it the way shown in the attachment, How is the water supposed to get into the tank? It's pushing against the air that is on the wrong side of the bladder, right? Where is that air going to go? The water the operator introduced to the system illustrates my point. It DID NOT go into the tank.

4. Why have a bladder at all if you're going to have air on both sides of it anyway?

5 Anyway you look at it, an upside down bladder tank will collect air on the wrong side of the bladder, defeating its intended purpose. (See picture attached.)

6. Yes! I understand that a gas compresses but this fact alone does not explain what was observed.

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psb75

A bit of confusion here. You have supplied two photographs and they contain a total of THREE different tanks. Please indicate WHICH tank in the photo you are having trouble with. Three tanks: 1. gray, 2. red. 3. blue. If the tank is entirely empty of water, that is not right. The side of the tank that has the pipe connection should have water in it. Your system pressure should be relatively low. Under 20 psi. The 'other' side of the tank should be hollow—when tapped or rapped on. You can only test the air pressure with the tank isolated from the system. An expansion tank can be mounted in any orientation. The writing on the tank orientation is meaningless.

psb75

The blue tank —not an "Extrol" tank (#PFX T121), appears to be on the supply side of a domestic gas heated water heater. It is NOT on the heatring system. The tank pressure on that system will should be higher—28 or 38 psi. i.e. 2 psi. below the "cut-in" setting on the pump switch.

Intplm.

When you take a pressure reading on the air side there should be NO pressure on the water side influencing the the reading. This is probably why the gauge when taking said reading "pegged".

Simply put, and as an example, the tank must be charged to the system water side operating pressure. In a residential, and on many commercial settings, the setting for air is commonly 12-15 psi. The water side should also be set at the same pressure through a pressure reducing valve.

I have seen many tanks installed with many different orientations. Up, down, angled, offset etc. When the tank is properly charged with air to the corresponding systems working pressure they work correctly.

GroundUp

There is nothing wrong with that mounting orientation. How did he determine that the water side was dry? There is no drain or test port there to check. If it's not taking water without spiking the pressure, something is closed, the bladder is compromised, or the charge is wrong. The water side needs to be dropped to zero before fiddling with the air side. Once that water side is open (maybe disassemble the union after the valve is closed), fill the air side to whatever the desired water side pressure will be. Use two different low pressure gauges, not a regular automotive tire gauge. When that's set, reassemble the water side and fill to desired pressure. All done, unless the bladder is compromised.

hot_rod

I spoke with a number of expansion tank factory folks this week, they are not concerned about orientation on diaphragm tanks

mattmia2

The precharge needs to be checked once a year or so, the schrader usually leaks a little and i'm not sure the bladder is completely non-permeable to gasses, it leaks out over time.

Any air in the water side of the tank should get removed by your air elimination if you have good air elimination. Water flows in and out as the system heats and cools and when the system is cold, if the precharge is correct, the bladder should be almost completely collapsed toward the water side. If the air elimination is correct then this flow of water in and out should scavenge any remaining air.

Kaos

I think the way it is installed it will collect air in the system over time similar to a compression tank. The issue is that since the bladder won't let this air rise to the top, each the system system cools down and the pressure drops, this air is pushed back into the heating loop. I guess over time the air eliminator will remove it but will take many cycles.

ccstelmo

Yikes!

I always get down in the dumps when I fail to explain a situation succinctly. Paragraph 3 of my original post was my best effort at describing the piping and I was sure the photo cinched it. The red tank is the expansion tank, the gray tank is the air separator and I wish I'd never mentioned the blue tank because it just created a distraction. I just thought it was a good example of how air could get on the wrong side of a bladder. Oh well.

I do appreciate all the input but frankly I don't find any of it really speaks to the issue. I'll just put my tail between my legs and walk off stage here but will offer one final question. If it doesn't matter if air is on the wrong side of the bladder then why do you all suppose anyone ever invented a bladder tank? My understanding has always been that it was because someone thought it would be a good thing to keep the water and the air from coming into contact with each other. What I get from you all is that you don't agree and, hot rod, that the manufacturers don't seem to agree either. Go figure.

As for me, I'm going to keep on piping bladder tanks so that air is not encouraged to enter the water side.

ccstelmo

Alan (California Radiant) Forbes

Whether air or water is on the water side of the x-tank is of no issue. The important thing is the air side that allows the water in the system to expand and contract when properly charged.

I've seen x-tank instructions that say that they should only be mounted vertically and I've called manufacturers that have said that this is for support considerations only. When properly supported, vertical mounting is considered fine.

mattmia2

A bladder tank allows you to use automatic air elimination in the system. without the bladder separating the air that is compressed to allow for expansion from the system, automatic air elimination would remove the air cushion from the tank over time.

hot_rod

the air in the tank is compressible, so as the water expands, pressure increases, it will push into the space regardless of the position of the tank.
The manufacturer doesn’t know which position it will be mounted when affixing the label

No reason the tank needs to be above the boiler, base mount styles are usually on the floor next to the boiler.

There have been instances where a new tank has the diaphragm stuck against the nipple and will not accept water. Increase the fill pressure until you hear it pop, or some suggest pushing a wooden dowel against the epfm.

GroundUp

If you're concerned about being succinct, perhaps answering the questions you've been asked would be a step in the right direction. We're all trying to help you, but that's impossible when you don't provide the necessary information which is requested of you. Again, how did he determine that the water side was dry? Was the described pressure adjustment process followed?