Typical or allowable air in pumped water system
Typical or allowable air in pumped water system
(OP)
I am testing products in a swimming pool-type test facility in which self-priming pool pumps pull water from a bottom drain and discharge to a submerged level in an open tank. There are no other sources/discharges. The test is to suddenly block the bottom drain. The tested products are designed to eliminate the ensuing suction pressure drop as fast as possible. Air entrainment is an issue and I am set about to measure and record the amount of air that enters the suction side.
To measure, I drain and cap the suction pipe and evacuate with a vacuum pump to the level I expect to see when the drain is blocked (24-27 in Hg). I calculate a figure in cubic inches per minute.
My question is, what is a normal, allowable, suitable, etc., amount of air to enter such a system? Is there a rationale for a benchmark?
To measure, I drain and cap the suction pipe and evacuate with a vacuum pump to the level I expect to see when the drain is blocked (24-27 in Hg). I calculate a figure in cubic inches per minute.
My question is, what is a normal, allowable, suitable, etc., amount of air to enter such a system? Is there a rationale for a benchmark?





RE: Typical or allowable air in pumped water system
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RE: Typical or allowable air in pumped water system
Is the entained air a product of these devices and if so where do you expect the entrained air to come from?
RE: Typical or allowable air in pumped water system
I apologize. My questions are ' how much air leakage is "normal" for the suction side of a water piping system'? Is this measured? How? The rest of my post was background information to show what I was doing. The 'tested products' react to a blockage at the pool drain by, for example, stopping the pump. Performance can be susceptable to air entrained in the water.
RE: Typical or allowable air in pumped water system
Perhaps the easiest way to measure entrained air would be to try collecting the accumulating air bubbles at the top of a bubble column after discharge pressure letdown.
http://virtualpipeline.spaces.msn.com
RE: Typical or allowable air in pumped water system
So, if I evacuate dry pipes and get a pressure rise from 24.5 to 22 " Hg over 3 minutes, that's too much? You're saying there should be no measureable change in pressure over 3 minutes?
How is this Bubble column test performed? Do you know of a site?
RE: Typical or allowable air in pumped water system
http://virtualpipeline.spaces.msn.com
RE: Typical or allowable air in pumped water system
The devices are products that are designed to eliminate body entrapment on a pool drain.
But the products are incidental to what I need to determine: does my test facility pass along an unacceptable amount of air? Since my facility models a swimming pool, which is open, a certain amount of air is expected. This dissolved air and any leakage air from joints are comingled. I need to know the dissolve air part for an open tank/pool situation.
And yes, some of the tested products are designed to let air in to exact a cavitation-like loss of suction at the pump--this frees the drain blockage. But that is designed to occur. I must make sure I don't allow air in before this device operates so that my facility affects how the device operates.
RE: Typical or allowable air in pumped water system
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You're going to get that much air through the pump, exactly as would a swimming pool. But you're interested in entrained air, which could be anything, depending on how much mixing the water has undergone with air prior to being taken in to the inlet. And soluble air will stay in the water as long as its at the same P & T, so to measure entrained air, run the discharge stream at a very slow velocity and at atmospheric pressure through a bubble column. Measure the volume of air collected in the top of the column over a given time at a given flowrate.
So, now you will probably ask me how much entrained air is normal in swimming pool water. I don't have a clue, but if I needed to know, I'd go get some water samples from 10 different swimming pools and let them sit at 20ÂșC for 24 hours.
http://virtualpipeline.spaces.msn.com
RE: Typical or allowable air in pumped water system
Thanks for the very helpful threading. One more question: how do I build a bubble column?
RE: Typical or allowable air in pumped water system
This is gonna' look great on the C.V.
http://virtualpipeline.spaces.msn.com
RE: Typical or allowable air in pumped water system
We used to test gas separators and used this system to see how much gas was being entrained.
If you only find a couple of % then I wouldn't worry about leaks. There will always be some gas.
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RE: Typical or allowable air in pumped water system
I would offer the comment re the above, no air leakage in "normal" in a properly installed installation.
As for measuring the amount of air contained in a swimming pool I would suggest that you contact a company or engineer involved in water treatment, they can give you advice etc, on how to go about this.