[Norminn]

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.

[dpb]

Jeff Wisnia wrote:
....

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.
....
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.

--

[Jeff Wisnia]

Norminn wrote:
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.


Someone's head(s) should roll over that kind of sloppy oversight and
maintenance.

But, I was puzzled by this line from the story:

********

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.

********

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.)

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.

[JoeSpareBedroom]

"Jeff Wisnia" wrote in message
...
Norminn wrote:
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.


Someone's head(s) should roll over that kind of sloppy oversight and
maintenance.

But, I was puzzled by this line from the story:

********

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.

********

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.)

--
Jeffry Wisnia


What about the suction being added by the pump which sends the water to the
filter?

[beecrofter]

On Jul 5, 4:15 pm, Jeff Wisnia wrote:
Norminn wrote:
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.

Someone's head(s) should roll over that kind of sloppy oversight and
maintenance.

But, I was puzzled by this line from the story:

********

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.

********

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.)

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.

wanna bet 300lb/sq ft

[Jeff Wisnia]

dpb wrote:

Jeff Wisnia wrote:
...

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.

...
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.

--

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.

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.

[Jeff Wisnia]

beecrofter wrote:

On Jul 5, 4:15 pm, Jeff Wisnia wrote:

Norminn wrote:

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.

Someone's head(s) should roll over that kind of sloppy oversight and
maintenance.

But, I was puzzled by this line from the story:

********

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.

********

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.)

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.


wanna bet 300lb/sq ft


I'll bet WITH you on that one...

That's why some poor souls have gotten "stuck" onto a pool drain and
couldn't generate enough push or lift to get themselfes freed before
they drowned.

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.

[SteveB]

"Jeff Wisnia" wrote in message
...
dpb wrote:

Jeff Wisnia wrote:
...

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.

...
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.

--

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.

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.


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

[SteveB]

"Clark" wrote

You're close Steve. Fresh water is 0.433 psi/ft. I believe that 0.45 is
commonly used for salt water.

Commercial diver's training school was many years and many brain cells ago.
I knew there was a .433 in there somewhere.

Steve

[dpb]

Jeff Wisnia wrote:
dpb wrote:

Jeff Wisnia wrote:
...

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.

...
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.

--

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.


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...

--

[Nancy Young]

"Jeff Wisnia" wrote

That's why some poor souls have gotten "stuck" onto a pool drain and
couldn't generate enough push or lift to get themselfes freed before they
drowned.

Because of this problem, where I live places had to replace their
pool drain covers with the type where long hair could not get
caught, and they couldn't trap people the way that little girl was,
either. Why aren't they mandatory everywhere, you'd think the
insurance company would have insisted on it.

nancy

[mm]

On Thu, 05 Jul 2007 20:17:01 GMT, "JoeSpareBedroom"
wrote:

What about the suction being added by the pump which sends the water to the
filter?

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.

[Norminn]

Nancy Young wrote:
"Jeff Wisnia" wrote


That's why some poor souls have gotten "stuck" onto a pool drain and
couldn't generate enough push or lift to get themselfes freed before they
drowned.


Because of this problem, where I live places had to replace their
pool drain covers with the type where long hair could not get
caught, and they couldn't trap people the way that little girl was,
either. Why aren't they mandatory everywhere, you'd think the
insurance company would have insisted on it.

nancy



I know there was an accident similar to the one in Minnesota not long
ago...a year or two? Another child, I believe, had their abdoment
ruptured and their intesting sucked out. The little girl in Minnesota,
afterwards, asked her mom if she would be on the news. She wondered
because she didn't want it to happen to anyone else. That is a heroic
child...traumatized beyond belief and then thinking of others. I can't
imagine how the parents feel. So, I thought readers might take her
hopes to heart and make sure it can't happen where they live.

[Norminn]

mm wrote:

On Thu, 05 Jul 2007 20:17:01 GMT, "JoeSpareBedroom"
wrote:

What about the suction being added by the pump which sends the water to the
filter?


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.

Atmospheric pressure in this case is irrelevant.....it was the pump that
did the damage. Once her body sealed off the inlet, the pressure would
continue to increase unless there was some sort of limiter on the pump
or the pump failes. They found her intestines in the pool filter, for
gosh sakes!

[mm]

On Fri, 06 Jul 2007 01:29:17 GMT, Norminn
wrote:

mm wrote:

On Thu, 05 Jul 2007 20:17:01 GMT, "JoeSpareBedroom"
wrote:

What about the suction being added by the pump which sends the water to the
filter?


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.

Atmospheric pressure in this case is irrelevant.....

You made the article sound upsetting and I didn't look at it. But we
've been discussing water pressure and pumps and partial vacuums, and
if there were no atmospheric pressure, or if it were low like on some
planets, I don't believe the pump would have been able to suck as
much, no more than the atmospheric pressure plus the water pressure.

Even some bigger and more massive planets than ours, have, I believe,
less atomospheric pressure, because that pressure increases as the
mass of the planet inceases, but decreases as the mass of the
atmosphere decreases.

it was the pump that
did the damage.

Atmospheric pressure is invisible, but it's there.

AFter going to to the trouble to warn me about how depressing the
artcile would be, you then had to print some of it below, snippped.

[SteveB]

"Clark" wrote in message
...
"SteveB" wrote in
:


"Clark" wrote

You're close Steve. Fresh water is 0.433 psi/ft. I believe that 0.45 is
commonly used for salt water.

Commercial diver's training school was many years and many brain cells
ago. I knew there was a .433 in there somewhere.

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.


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

[SteveB]

wrote in message
...
On 6 Jul 2007 00:08:26 GMT, Clark wrote:

"SteveB" wrote in
:


"Clark" wrote

You're close Steve. Fresh water is 0.433 psi/ft. I believe that 0.45 is
commonly used for salt water.

Commercial diver's training school was many years and many brain cells
ago. I knew there was a .433 in there somewhere.

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.


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.

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

Steve