Typical or allowable air in pumped water system 1

[mrelet]

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?

 

[BigInch]

Sorry, but I've got no idea what you are really trying to do or why. Want to explain it a little better?

http://virtualpipeline.spaces.msn.com

 

[Artisi]

Are "The tested products" some sort of pressure relieving device that will open if and when the inlet is suddenly blocked, does it open to atmosphere or is it submerged underwater?

Is the entained air a product of these devices and if so where do you expect the entrained air to come from?

 

[mrelet]

BigInch and Artisi--
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.

 

[BigInch]

I would think that you would want to allow for entrained air content of the water to somewhere around 1-2% by volume. At 5% you might have noticable degradation of pump performance, depending on type of pump you're testing. "Normal leakage" through pipe joints should be close to zero if well fitted. If your pump suction can get all the way down to 0.5 psia, you'll start cold boiling and making vapor yourself, but probably cavitation will start well before that, but that vapor is not "entrained air", its water vapor.

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

 

[mrelet]

BigInch (Petroleum)

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?

 

[BigInch]

I have no idea. You say you are testing "products", but don't tell us anything about what exactly you are testing. All we know is, "The tested products are designed to eliminate the ensuing suction pressure drop as fast as possible.", but have no idea about what they are doing, or how those devices are supposed to perform. Do they let air into the suction pipe? Are they another suction line with a solanoid valve to allow water into the suction from another source? Are they connected to a water reservoir? I don't know. Otherwise, why are you getting any pressure rise? I wouldn't expect any in a closed off system. Is air and water backflowing from pump discharge through the pump into suction? Is air or water leaking in from an incompletely blocked drain inlet? Why would you expect leakage of air or water into the suction? Bad pipe joints???

http://virtualpipeline.spaces.msn.com

 

[mrelet]

BigInch (Petroleum)

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.

 

[BigInch]

quantity of soluble air in water is here,

http://www.engineeringtoolbox.com/air-solubility-water-d_639.html

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 20ºC for 24 hours.

http://virtualpipeline.spaces.msn.com

 

[mrelet]

BigInch (Petroleum)

Thanks for the very helpful threading. One more question: how do I build a bubble column?

 

[BigInch]

Sorry about the apparent backflow in the diagram, but I'm sure you get the idea. If you can locate the column so the vent outlet is near the pump maximum discharge head, you can probably eliminate the pressure control (letdown) valve going to the bubble column.

This is gonna' look great on the C.V.

http://virtualpipeline.spaces.msn.com

 

[EdStainless]

I have seen systems where there is a simple "T" in the line with a vertical pipe on it. The simple ones use clear material for the vertical pipe. If you install a larger diameter section of pipe after the pump discharge the flow will be very slow and any non-disolved gases should separate and rise in vertical leg.
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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[Artisi]

My questions are ' how much air leakage is "normal" for the suction side of a water piping system'? Is this measured? How?

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.