Horrible Pool Accidents, Pump Covers

I just read an article about a horrible injury to a little girl in Minnesota. This happened in a wading pool and it is difficult to read about. Here is a link to the story: http://wcco.com/topstories/local_story_185085504.html
It is summer and pool time, so take care of the little ones.
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Norminn wrote:

Someone's head(s) should roll over that kind of sloppy oversight and maintenance.
But, I was puzzled by this line from the story:
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In most public pools the drain cover is screwed in and cannot be pulled off. According to the Consumer Product Safety Commission, the pressure on some pool drains can be as strong as 300 pounds per square inch.
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I don't see how a pool drain could suck with a force of more than one atmosphere (14.7 psi) plus about another 1/2 psi for every foot of pool water depth above the drain.
I think they must have meant a "total force" of 300 pounds sucking something down against a drain opening of about 20 square inches or so.
Jeff (Hoping he hasn't forgotten his high school physics.)
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Jeffry Wisnia
(W1BSV + Brass Rat \'57 EE)
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Jeff Wisnia wrote: ...

... In large pools certainly, they're not atmospheric drains, they're inlets to recirculating pumps so it's dependent on the suction head plus the static head.
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dpb wrote:

Yes, and if that's the case, how come a suction well pump can't lift water more than about 25 feet and you have to use a submerged pump for a deeper well?
300 psi is the equivalent of about 660 feet of water depth.
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Jeffry Wisnia
(W1BSV + Brass Rat \'57 EE)
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Not really. Each 33' equals 14.7psi, therefore, each foot is .4545454545 psi. The psi for 660' would be 294. Slightly different in salt water.
However, you did say "about", so you're pretty close.
Steve
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You're close Steve. Fresh water is 0.433 psi/ft. I believe that 0.45 is commonly used for salt water.
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Commercial diver's training school was many years and many brain cells ago. I knew there was a .433 in there somewhere.
Steve
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wrote

There aren't very many folks that have to be concerned about the small differences.
Where'd you dive? I worked with divers in the GOM a few times.
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I think you folks missed the "300 pounds per square FOOT" That is a couple PSI, 55-60" of water, certainly well within the suction head of a pool pump. The fix is simple, a vent to air and/or a second drain path. That's why one or both are required in the code. In my pool I have 3 parallel drain paths and a vent.
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snipped-for-privacy@aol.com wrote in wrote

is
Who are you addressing? We're discussing gradients at this point, well past the design problem.
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wrote

Once you have your face underwater, it's all pretty much the same.
Steve
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wrote:

The point is, if you have multiple drain paths and /or a vent you are only fighting the water column, not the pump.
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On Fri, 06 Jul 2007 11:01:04 -0400, snipped-for-privacy@aol.com wrote:

Actually after playing in my pool tonight and screwing with the vacuum port I change my vote. You also have to take into account the inertia of all that water in the pipe. The static suction is limited by the head at the vent or other opening but the instant suction while that water is slowing down is much higher than even the pump can create approaching one atmospherre plus the water column. That is the water hammer effect
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wrote

I worked in the Gulf of Mexico for Norman Industries and Global Divers from 1974 to 1980. A couple of years sprinkled in there as crane operator for Reading and Bates, and welding for assorted companies.
Steve
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wrote

Ah, well before me then. I was in the gulf in the early 90's.
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Jeff Wisnia wrote:

I came back to check and of course(!) you'd already beat me, Jeff... :)
I realized after walking away I had _read_ 300 but _thought_ 30... :(
Me culpa...
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Suction head plus hydrostatic cannot exceed atmospheric pressure plus hydrostatic. In fact suction head really can't get near atmospheric 'cause you'd get cavitation. Remember, there are no negative numbers on an absolute pressure scale.
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What kind of building code can you have if you don't require multiple drain paths and vents to air on a commercial pool? Are the underwater lights mechanic's drop lights?
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What about the suction being added by the pump which sends the water to the filter?
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On Thu, 05 Jul 2007 20:17:01 GMT, "JoeSpareBedroom"

I believe that even if there were a total vacuum below the water drain, the maximum pressure would be the weight of the water and air above the drain. That's the principle of a mercury barometer (except that there is a vaccum in the tube above the mercury instead of below it), and if water barometers were made 600 feet tall, that would be the principle there too.
I don't think suction really exists. All there is is unresisted pressure, and the pressure is caused by the weight of the atmostphere (and the water, when something is under water.)
Sort of like centrifugal force doesn't really exist (that is equal and opossite to the centripetal force, as elementary school science books sort of said). All there is is inertia that tends to make the something go straight ahead, perpendciular to its axis of rotation, not away from teh center of rotation.
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