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Old January 14, 2008   #1
tuk50
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Default Water Hydraulics?

I need some engineering help! Setting up a water system in tomato patch. I have a couple of 55gal barrels 2ft off the ground gravity fed through a 3/4in hose connecting them to a pvc 1/2in system. The 5 30ft 1/2in pvc lines are connected at one end with pvc T's and capped at the other 5 ends. The 1st 30ft row to the 5th 30ft row has about a 10in drop over 25ft. Question is where do I drill small holes and where do I drill larger holes to keep some sort of equal pressure in all the lines. Do larger holes need to be at the capped ends of the 30ft lines or at the 5th row, which is the fartherest away from the 3/4in hose supply. I'm sure it is obvious for a hydrologist, but I ain't one. .. LOL..
Also I thought about starting with 1/4in holes every 2in and using progressively smaller bit sizes toward the higher pressure side, is this about the right size holes or should they be smaller.
I have to put so much water on my maters here in the desert that I want to let the water dechlorinate for a day or two prior to irrigating, plus making a weak compost tea each day. 8)
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Old January 14, 2008   #2
Worth1
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I don't have a license But I have a lot of knowledge on hydraulics.

What you are thinking is (I'm sorry to say) a little off, let me get my mess picked up and I will be back with you later and I will tell you what you need to do.
What you need to do now is tell me where the line is connected to the barrels, top or bottom.
I would also like to know how much pressure you THINK you have.

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Old January 14, 2008   #3
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Holey mackerel! That’s a tough one!

First of all, water pressure in the pipes will vary. “Hydraulic head (water pressure)” or “static head” will go from high to low as water level drops in the tanks. Water flow is directly proportional to pressure, so it will be very difficult to control flow in the pipes if pressure changes.

Assuming the branch pipes are level relative to ground, as long as water pressure is maintained, then water pressure will be equal throughout the pipe from one end to the other (water friction and viscosity should not be too important for a 1/2 pipe 30’ long) , therefore the holes need not vary in size for even flow.

To maintain even water pressure within the pipes, the total flow from all the holes in all the pipes should not be more than the flow from the main pipe from the tanks, otherwise equal pressure inside the pipe cannot be maintained.

In you case, there is one pipe that’s lower at the end by ten inches, therefore the water pressure will be higher at the end of the pipe and more water will come out from the holes.

It will be very difficult to control water flow by varying hole sizes, I would suggest instead, use same size hole but vary the distance between holes. You will need to drill very tiny holes so that you don’t lose water pressure. ¼” is way way too big.

You can try using these micro drill bits:

http://www.harborfreight.com/cpi/cta...emnumber=34640

50 PC.SOLID CARBIDE MICRO BIT GRAB BAG

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Last edited by dcarch; January 14, 2008 at 08:58 PM.
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Old January 14, 2008   #4
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So dcarch how much water pressure do YOU think he will have at the head end of the pipe?

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Old January 14, 2008   #5
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Quote:
Originally Posted by Worth1 View Post
So dcarch how much water pressure do YOU think he will have at the head end of the pipe?
Worth
I guess it would be, when the tank is full, the total weight of the water column which would be 24" + 33" (approximate height of a 55 gallon drum).

I forgot the weight of water . Stop pressuring me

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Old January 14, 2008   #6
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I put the faucets at the bottom of each barrell and the top is not sealed, just gravity with the barrells setting 24in's high on platform. The pressure or flow rate is not as important to me as even distribution over the mater patch. Is 1/8in holes small enough, I was just concerned about plugging up from dust and etc. that will blow into open barrels. I plan on just opening the valve each morning to let the water drain at its leisure while I go on to work. That way each barrel will have time to rid itself of some of the chlorine before I need it. 8)
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Old January 14, 2008   #7
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So, 5th row 1/8in holes 6in's apart, 4th row 5in's apart, 3rd row 4in's apart etc. ?8)
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Old January 14, 2008   #8
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I would just install pressure compensating drip emitters designed for gravity fed systems where you want them (they will all emit at the same rate as long as you hav the source high enough and don't kill the pressure with excessive friction loss due to long runs. ) 1/2" poly tubing and emitters are cheap and they take the guesswork out of the job. .

You may find this link very helpful http://www.dripirrigation.com/drip_i...hp?pgv=Gravity
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Old January 14, 2008   #9
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Also is you have holes in a pipe at different elevations (You said it runs downhill)and a low pressure system the water will not fill the pipe entirely on the uphill side before it drains out of the downhill holes. That is why I recommend an emitter over a simple hole. You may also need to raise the barrell(s) Higher to get optimal pressure.
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Old January 14, 2008   #10
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thanks bryan, but I've got the pvc and barrels already set up and just trying to decide how many and the size of holes so they won't do what you said and empty from the lower end without filling the top end. I may have to just drill hole every couple of feet and experiment till it works. 8)
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Old January 14, 2008   #11
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Good luck, I hope you get it to work, just don't strip those reverse gears out until you are certain you have a working system. I love to experiment too. In this case you may not just want to modify the size of the holes but also the radial location of the holes in the pipe. For example, 12 oclock at the farthest downhill position rotating downward toward 4 or 5 ocklock towards the uphill side. This may help with the partially filled pipe.
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Old January 15, 2008   #12
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Dcarch and others,
Head pressure at 2 feet will be 2.60 psi at sea level and that is if the water level is 6 feet above ground and the place where the gauge is on the ground.
It doesn’t matter what the water weighs.
The formula I use is this.
At 10 feet above the ground the head pressure will be 4.33 so if the water tank was 100 feet off of the ground the pressure would be 43.31 psi.

This would be the pressure on your body if you were 100 feet under water too. (43.31 psi)
Psi doesn’t care if its ¼ pipe or 12 inch pipe it’s all the same.
What will be effected by pipe size is flow.
Sometimes you can cheat by going up on the pipe size to make up for the psi so you will get more flow.

So let’s say that one of the lines tuk50 has is lower by 10 inches the difference would only be about .43 pounds psi.
That’s less than 1/2 pound.
The easiest thing tuk50 can do is get a gallon jug and time how long it take to fill it from one hole of lets say 1/6 inch.
Then he can multiply this by how many holes he has and in this way he will be able to find out how long it will take to empty the tanks.

But there is a problem with this, the lower the tank gets the less pressure he will have.
Thusly the slower the water will come out.
If the tank is 2 feet above the ground then the pressure will only be .87.

Do you guys see where this is going?
There is another thing to consider, the siphon effect.

Let’s say that if you had at the faucet 100 psi and you had to go up 50 feet what would your pressure be?

Since 5X10 is 50 I would multiply 4.33 X 5 and come up with the answer of 21.65.
That’s how much pressure you would lose at 50 feet.
So the pressure 100- 21.65 would be 78.35.
Now here comes the siphon effect. If you then went back down 50 feet the pressure would go back up to 100 psi, SWEET.
This lerts you go up a hill then back down and have the sam pressure.

If you went down 60 feet instead of 50 feet the pressure would be 104.33 psi.
I won’t get into the friction loss in the pipe or the K factor of the emitters, tee’s and 90’s.
I do have manuals for this but I can’t find them right now.
It will be real easy to find out what these will be by experimentation.

Tuk50 if I were you I would forget the tanks and filter the water through 2 large carbon filters to get rid of the chlorine.

Put in a good drip system and forget all of the homemade pipe and holes.


You can get a nice drip system for a lot less than you will pay in the long run by trying to do it with a lot of home made stuff around the house.

I love to make all f my own stuff but even I have to draw the line somewhere.

DIG make a nice mid range affordable system and you can go on line and get every thing you need for a lot less then you think
Home depot sell DIG but they don’t sell everything the DIG makes.

I would suggest you get the ½ pipe 90’s and tees and what not from home depot and the ON OFF drip emitters from DIG direct as the home depot where I live doesn’t sell them.


You guys can check my math but I know I am dead on.
Not bad for a hillbilly kid that hated math.


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Last edited by Worth1; January 15, 2008 at 11:46 AM.
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Old January 15, 2008   #13
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The more I think about it, the slower I take it the better the results. I will start with a 1/32 drill and only drill a hole where the plants will be set out, this should easily fill the pipes and help me estimate how much pressure I will have so that I can add more holes as long as the pressure holds up.8)
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Old January 15, 2008   #14
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Quote:
Originally Posted by dcarch View Post
I guess it would be, when the tank is full, the total weight of the water column which would be 24" + 33" (approximate height of a 55 gallon drum).

I forgot the weight of water . Stop pressuring me

dcarch
A gallon of water weighs 8 1/3 pounds or 8.33

There are 7.5 gallons of water in 1 cubic foot.
55 gallons of water would weigh around 458.15 pounds and contain I think 7.3 cubic feet.

worth
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Old January 15, 2008   #15
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If I'm reading this right my head pressure will be from about 2.5 psi to about 1 psi, so at 1 psi how many 1/32 in holes can I drill before I have no pressure? Or is this optimistic and the holes need to be much smaller.
And I thought this was going to be an easy project.. LOL... 8)
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