Oxygen infusion through pump seals

JohnNY1

Is it only the people at Spirovent that claim the water in hydronic systems can become O2 starved and pull air in through various apurtenances? Or is it common knowledge?
Does anyone know where I can get some info on this? Believe it or not, there is a lot riding on it.

Thank you in advance.

Tony Conner

You Can Even...

...get this happening on big-BIG feedwater pumps pushing water into high pressure industrial steam boilers the size of two story houses. It's not so much oxygen starved water, as it is the suction pressure on the pump is too low, which is a mechanical problem, not a chemical one. (It'll show up as a chemical/corrosion problem, though.) The suction pressure falls just a little below atmospheric. Not enough to really show up in pump performance, just enough to suck a little air in around the pump seal.

In large plants, there's a tank affair called the deaerator. It's job is to get rid of dissolved air (specifically oxygen) in water before it gets pumped to the boiler. If it's set up properly, it'll take out 99.999% plus of the oxygen. Normally, sulphite is added to eat up any remaining oxygen. The chemical test for this is, surprise, the "sulphite residual test". You're ususally looking for 30 - 50 PPM of sulphite, then you know there's no loose oxygen. The feedpumps are installed below the deaerator, and pull water out of it, and discharge into the boiler. I've seen boilers get fed this water, and
STILL have oxygen pitting when they're opened for inspection. How could this be? The deaerator is working fine, the sulphite tests (usually run at least 3 times every 24 hours) are routinely right on. Improperly installed/piped feedpumps is the reason. High discharge pressure, multi-stage pumps will have the shaft packing/seal located at the suction end. This way, the seal only sees low pressures, as opposed to the pump discharge pressure, which is very often several hundred PSI. If the pressure at the suction falls below atmospheric - in comes the air, full of oxygen. And it goes right into the boiler, because all of the oxygen removal stuff happens BEFORE the water gets to the feedpump.

I have no doubt whatsoever that the same thing happens in little circ pumps on hot water heating systems.

Mark Eatherton1

Good point, except...

most residential wet rotor pumps don't have mechanical seals. They use an O ring. But even in that case, an O ring in not impervious to the transfer of oxygen. If there is an imbalance of 02 between the inside and the outside of a pipe, mother nature WILL find a way to balance it out. Either thru diffusion through non oxygen barier materials (which includes pretty much everything except metallic materials) or through the rubber diaphragm of the expansion tanks.

I am aware of some research that was done regarding the use of microbubble resorbers versus conventional scoop type air seperators, and the research found that both devices took the oxygen levels down to the same point. The resorber got there faster, but they both took it down to the same point.

Don't ask me how I know, I can not tell...

In the case of a conventional carbon ceramic seat style of pump seal assembly, yes, it will allow molecules of oxygen to pass through, while holding molecules of water back. There is usually an O ring seal around the base of the mechancial seal, and that too allows the transfer of oxygen.

What do you win?

ME

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Tony Conner

If The...

... air doesn't come in around the pump seal, it'll find a way in at a valve spindle, air vent, flange gasket, etc. If there's something below atmospheric pressure, air will find a way in. Even in big absorption chillers, where there are elaborate measures taken to maintain the vacuum, they still have to have vacuum pumps installed on the units. And you'll need to run it about 10 minutes a week, on a tight machine.

JohnNY1

The way I understand it is there comes a point when the system is overvented. That is, the vents become not only redundant, but self-defeating. The water then seeks to draw air, for its oxygen, in from any permeable source that it can.
True that?

Tony Conner

Is The...

...circ pumping toward the expansion tank? If it is, the tank pressure won't increase. It just sits there. (Check out "Books & More" on the menu list on the upper left of your screen, for "Pumping Away" - all will be explained.)Water still flows through the system, however, because the suction pressure of the pump falls. You'll still have a pressure differential due to the pump working. When the pump shuts off, pressure equalizes, and flow stops. If any part of the system falls below atmosheric pressure, that's when air will get sucked in until the pressure equalized to atmospheric. If you have an air vent located where the system pressure drops when the pump is running (assuming that's your situation) then air could be sucked in at that point.

hr

An interesting paper on this

was written by Dr. Kilkis and Mike Chiles. Written when the O2 barrier, or lack of, was big news. Apparantly in Europe there was a problem with thin steel pressed radiators being attacked when piped with "non metallic" tube. The report lists 7 sources of O2 ingress into radiant systems.

The DIN standard specifies three measures to prevent corrosion from O2 diffusion. One being barries tube, use of corrosion inhibitors, and the use of corrosion resistant pumps, valves, boilers, etc.

Barrier pipe alone may not be providing adequate corrosion protection. Probably why Tony watches the quality of inhibitors in the large, expensive systems he is involved in. If I were installing thin steel panel radiators I would be keeping close watch on the fluids!

I use corrosion inhibitors or inhibited glycol in every system I install now.

hot rod

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JohnNY1

Perfect. Any idea where I can find such a report? Perhaps on the web?

Thank you.

hr

I'll ask the authors

tomorrow if they mind me faxing to anyone interested. It can be found in the old Heatway binders, around 94-95 if you have access to any.

hot rod

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paul kiernan

heatway binder

good morning hr&master p,

i own a heatway binder dated 1995 that will be yours if it might help you. i am not sure if it contains the material you want. The majorityof the binder is devoted to there products. ther is one research report/ NO. 90-61 category 30. and there is a copy of conversion imformation information from a MR David Wirig to a MR Morty Schiff. It refers to mocon transmission rates among other things and is full of equations that frankly i do not understand. If this is what you need it would be my pleasure to pass it along. let meknow on the wall please, ill be around.
as always with respect
pk

ScottMP

Very interesting

All of this information is very interesting and important to our trade, but I dont think this was master plumbers reason for the question.

The party line from spirovent is that they remove SO much air form the system that the water is starved and will draw from anywhere it can. They claim you MUST use a diagphram tank or the system will "drain" a stell expansion tank.

Am I wrong M. Plumber, is that the root of the question.

By the way the response on commercial steam was quite informative but as ME said very few residential systems fall below atmosperic preasure on an average.

HR what type of inhibiters do you use, we install quite a few panels ?

Scott

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Tony Conner

Check Out...

...pages 12 & 13 in "Pumping Away" for the explanation on how you can have parts of your system run at less than atmospheric pressure, if you arrange the mechanical components the right (wrong?) way. I don't think anyone deliberately sets out to have their hot water heating system run in a partial vacuum.

ScottMP

your right Tony

> ...pages 12 & 13 in "Pumping Away" for the

> explanation on how you can have parts of your

> system run at less than atmospheric pressure, if

> you arrange the mechanical components the right

> (wrong?) way. I don't think anyone deliberately

> sets out to have their hot water heating system

> run in a partial vacuum.





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ScottMP

your right Tony

ands thats why I said on an average. Your right it is possible, I just felt his question sounded alot like what Spirovent told me. They felt they removed SO much water that it became " Horny " for air.

Scott



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hr

Okay to fax

If you would like a copy e-mail me your fax #

hot rod

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Tony Conner

I'd Like To Hear...

...the explanation behind the Spirovent claim.

I'm looking at my "Water & Wastewater Treatment Data Book" by Permutit. There's a graph on page 16 of my edition that shows the solubility of oxygen from air water at atmospheric pressure. It's in cubic centimeters per litre. At the freezing point, it shows "10". At about 120*F, it shows "4". At 212*F, it's "0". Take water to the boiling point, at whatever the pressure is, and you've driven out pretty much all of the dissolved oxygen. You can do this with just a pot on the stove. Granted, water moving in a pipe is different, in that the liberated air/oxygen will want to sail past an accumulation & discharge point. I can believe that the Spirovent unit can catch smaller bubbles faster than it's competitors, but I'm having problems with their claim of an end result that's "too much of a good thing". If you get from "A" to "B" in a minute, and the competition takes an hour to get to the same place, then that's good as far as it goes. If all you're looking for is the end result in reasonable time, then why care? As long as you're not adding make-up water that's full of oxygen, sucking air in, or having oxygen migrate through non-barrier tubing, then I'm not sure the harm is there. You may get a little bit of surface rusting from the tiny bit of oxygen that's left running around longer. Once the oxygen is eaten up by that small amount of corrosion, it should be insignificant in a tight system.

If nothing else, why would anyone state that "Our product is SO EFFECTIVE at removing oxygen from your heating system, that more oxygen just has to leak in. We're so much of a good thing, that our product will actually CAUSE the problem you've installed it to prevent!"

Maybe I'm missing something...

JohnNY1

Yes. But I was told at Wirsbo class in MN that it was the reason for things like 02 barriers. So I thought there would be more to it.