any math or engineering folks around?

[Kali]

looking for an on-line pressure calculator, or just the answer to this question/situation:

3/4 mile length, inch and a quarter PE (so I think that is inside diameter) pipe flowing by gravity down a 100 foot elevation. what is my water pressure at the bottom?

[Throck]

1. PE may be the type of pipe?

Polyethylene?

vs PVC.

[Kali]

2. correct

black thick walled plastic. heat-welded joints

[Throck]

3. Water static pressure problem.

43 psi or so.



https://www.google.com/amp/s/www.engineeringtoolbox.com/amp/pump-head-pressure-d_663.html

The length has no impact on a static system, only the 100' elevation differential.

[Kali]

4. thank you!

my well guy said it was probably around 40, but he was driving and I wasn't positive on the elevation until I got back to house and checked the topo. got the wrong kind of float valve. sigh. 3 day project turning into a month. LOL

[Throck]

5. Well system?

[Kali]

10. indirectly

the line in question starts at a 20x20 storage tank and flows by gravity to a drinker

[Yonnie3]

6. It depends on flow

With no flow it would be about 42 PSI

It would be less while flowing.

It has been three decades since I needed to make such calculations.

[JT45242]

7. Pressure at depth is an easy formula

P = Pnormal air + density of fluid*gravity acceleration* depth

P =1.013E5 pascals + 1000*9.8*30.5 meters = 400.2 kPsacals or just under 4 times normal atmospheric pressure (101.3 kPas)

In american units (thanks Reagan for taking us off of the metric system) 1 atm=14.7 lbs per square inch

So, really close to 58 pounds per square inch

The more 'junk' in the water, the greater the density of the water which would make the calculation go up.

[Kali]

11. uh...

that pretty much just confused me more. also we are talking about an elevation of 4000 feet above sea level - does that complicate it even more? and the pipe is on the surface of the ground in the sun, I am guessing the water is getting close to 150 degrees F.

[Takket]

8. Is your pipe open to atmosphere at top? Is it open at the bottom allowing water to flow out?

Water imposes 1 foot of head for every 1 food of elevation. 2.31 feet of head equals one psi. If your pipe is open at the top and closed at the bottom the pressure is 43psi. If the pipe is open at the bottom the pressure is just atmospheric.

[Kali]

12. sort of

it is flowing by gravity out of a big 20 x 20 foot tank.

[genxlib]

9. I think you got the answer you need but let me correct one thing

The relationship of nominal pipe diameter to actual pipe diameter is a little misleading. It depends on the thickness of the pipe.

Pipe comes in various thickness so it can be used for various conditions such as high versus low pressure. However, it is the outside diameter that is held constant so that fittings can be standardized to work with all of the versions. So when the thickness of the pipe wall varies, the inside diameter is the dimension that changes. For thick wall pipe, it can be significant.

The easiest place to recognize this is in PVC. If you compare Schedule 40 to heavier Schedule 80, the inside diameter of the S80 is only 3.75"

PE pipe is sold in a whole range of strengths based on the DR which is a measurement of the ratio of the diameter to the wall thickness. At the weakest end, that inch and a quarter pipe actually has an inside diameter of 1.53" while the heaviest version is 1.186". Meanwhile the outside diameter remains constant at 1.66"

The differences can get really significant in larger pipe. At 12" , the ID is actually close to 9" because the walls are so thick.

https://www.engineeringtoolbox.com/ASTM-D3035-PE-pipes-d_2138.html

[Kali]

13. I stand corrected

we bought the pipe well over a year ago and I am sure I knew more at the time. that stuff does not retain well in my brain AT ALL.

in fact I think I had the DR more recently because we had to find the metal ends fast once the guy with the welder was ready. lots of new learning that fades quickly if you don't need it again regularly.

[panader0]

14. I'm no expert but I believe that if you want to increase the pressure at the bottom,

you can if you reduce the diameter of the pipe as it goes down.
Off topic, how's the water supply at your place? I've had so little rain it's pathetic.
I looked up a USGS site on line and entered my zip code and nearby registered wells have fallen between
10 and 12 feet in the last ten years. When I bought my forty acres here in '78, I had the only well around.
Now there are many neighbors and all have to have wells. I fear for the future of my well. Have you ever
had a well deepened? If so, how much did they charge? C'mon rain.

[Kali]

15. no, the opposite actually.

bought a big bronze float valve and it wasn't holding because of too much pressure, so had to get a different type.

Actually we are doing ok, knock on dry wood. I just did a zoom ranchers meeting last night and two people have completely destocked and wells gone basically dry. we partially destocked and I need to do more, as we are just about out of old dry grass now and the cows left are happy to be eating mesquites at the moment. If we don't get rain this July-August it will be time to start a trailer park I, am afraid.

I have not had to lower a well (though we lost two hand dug wells in the last decade, but they were 25 to 30 feet deep and basically surface water) but I understand it is pretty expensive. I hope yours holds out! Hauling water SUCKS, even if just for household use.

We are pretty (overly) dependent on rain filled stock ponds and one deep well that is FAR away.

[Kali]

18. clouds, THUNDER,

and ten sprinkles this afternoon!

[Klaralven]

16. Water weighs 62.4 pounds / cubic foot.

So column of water 100 feet high would weigh 6240 pounds.

To convert from the 6240 pounds / square foot at the bottom of the column divide by 144, the number of square inches in a square foot.

6240 /144 = 43.3 pounds per square inch of pressure.

Since water is a liquid, it doesn't matter whether the column that is 100 feet tall is straight up and down, or really slanted like your pipe. If the water is standing still all that matters is the difference in elevation.

If the water is flowing freely, then the pressure at the outlet is essentially zero, and all the pressure difference is taken up by friction between the flowing water and the wall of the 3/4 mile long pipe.

[Ptah]

17. This thread is a great example of DU Knowledge.