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Anonymous Poster

Size of Hole for 1 Litre/Minute Flow Rate?

09/16/2010 5:53 AM

Hello,

Could anyone inform me if there is a formula/ratio for working out the size of hole required for a 1 Litre/minute flow rate?

The case in question is a non pressurised pipe with a head of water of 3-4 m which needs to be drained at a constant rate of 1 litre/minute by drilling a hole in the bottom.

Any thoughts would be welcome,

Thank you.

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Guru
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#1

Re: Size of hole for 1 Litre/minute flow rate?

09/16/2010 6:05 AM

No, there isn't. The flowrate will vary with the drop in head as the pipe empties.

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Anonymous Poster
#20
In reply to #1

Re: Size of hole for 1 Litre/minute flow rate?

09/17/2010 5:28 AM

But if the tank of fluid is being replenished at the same rate as you need to empty, then head pressure should remain quite constant me thinks???????

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#29
In reply to #20

Re: Size of hole for 1 Litre/minute flow rate?

09/17/2010 4:06 PM

If the tank fluid was being replenished at the same rate as it is being emptied there would be no need for the tank, right?

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#2

Re: Size of hole for 1 Litre/minute flow rate?

09/16/2010 7:08 AM

1L/m is pretty slow.
You will only get a constant flow if you have a constant head.

A standard 15mm plumbing fitting easilly exceed 1L/m. at that head (I'd guess you'd get about 3or more L/m) So use that and put a stop cock or valve on it so that you can adjust the flow.
Cheap simple effective.
if you want even cheaper just drill a 3mm hole, measure the flow and enlarge or drill more holes until you reach the desired flow.

Doing it empirically or adjustably is the only sensible way. All the calculation in the world won't actually make it happen.

Del

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#22
In reply to #2

Re: Size of hole for 1 Litre/minute flow rate?

09/17/2010 6:40 AM

Good answer Del

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Anonymous Poster
#3

Re: Size of Hole for 1 Litre/Minute Flow Rate?

09/16/2010 8:21 AM

Purpose?

How constant the flow you want to be?

As mentioned the rate will be dependant upon the static head If you want the flow to be constant, force it (put a pump of 1LPM to drain the water may be PD Pump if you want it to be really constant)

UD15

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#4

Re: Size of Hole for 1 Litre/Minute Flow Rate?

09/16/2010 8:44 AM

Listen to the Cat. Just install a cheap ball valve and throttle it as need be.

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Anonymous Poster
#5

Re: Size of Hole for 1 Litre/second Flow Rate?

09/16/2010 9:12 AM

I should have said a maximum flow of 1 Litre per minute, its a environmentally related project to drain a lagoon at a set rate. I believe it does not matter if the flow falls below that rate just that it doesn't exceed it.

Also have a project that needs draining at a Litre per second! Any rough ideas on the size hole that would need? Again drop off in rate towards the end isn't a problem just that it doesn't exceed a maximum.

Thank you for your help gentleman.

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#23
In reply to #5

Re: Size of Hole for 1 Litre/second Flow Rate?

09/17/2010 7:14 AM

I make it a 1.97mm dia. orifice at 4m head. I'd have thought 2mm would be near enough.

Cheers...........Codey

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#25
In reply to #23

Re: Size of Hole for 1 Litre/second Flow Rate?

09/17/2010 12:21 PM

I hadn't noticed the other posts where it went to 1 litre/sec. For that flow orifice dia comes to 15.2mm. Coefficient of discharge is close to 0.62.

Cheers.........Codey

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#6

Re: Size of Hole for 1 Litre/Minute Flow Rate?

09/16/2010 10:15 AM

Of course if you want a constant rate, you simply attach the hole to the end of a flexible pipe.
The end of the pipe is mounted via a rod or some shuch linkage to a float so that as the water goes down so does the end of the pipe thus maintaining a constant head.
(Yes really, trust me I'm a cat...it will work)
Del

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#33
In reply to #6

Re: Size of Hole for 1 Litre/Minute Flow Rate?

09/19/2010 11:41 PM

GA Del. Good old simple idea

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#7

Re: Size of Hole for 1 Litre/Minute Flow Rate?

09/16/2010 10:52 AM

I have to agree with the furry one. I'd use a ball valve to adjust the flow in both cases.

I think debris will be your enemy. A small hole will be more prone to clogging, too.

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Anonymous Poster
#11
In reply to #7

Re: Size of Hole for 1 Litre/Minute Flow Rate?

09/16/2010 11:56 AM

Lynlynch, where you been sir,i didn't see you discussing the threads for more than week.

Are you busy with your neighbor wireless connection?

Ragab - Syria

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Anonymous Poster
#14
In reply to #11

Re: Size of Hole for 1 Litre/Minute Flow Rate?

09/16/2010 12:52 PM

How you know Ragab,are you prophet then ?

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Anonymous Poster
#17
In reply to #11

Re: Size of Hole for 1 Litre/Minute Flow Rate?

09/17/2010 1:53 AM

Ragab,

the only one messing with the neighbors wireless is you.

O sorry I forgot, you did ask the forum to help you becaue you could not work it out yourself.

Ashame on you!

Werner

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Anonymous Poster
#26
In reply to #17

Re: Size of Hole for 1 Litre/Minute Flow Rate?

09/17/2010 1:05 PM

Thank you sir for your advice.

What is the website available for help?

Ragab - Syria

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#27
In reply to #17

Re: Size of Hole for 1 Litre/Minute Flow Rate?

09/17/2010 1:35 PM

Thank you sir for your help.

You can help me by sending me PM.

Ragab - Syria

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Anonymous Poster
#8

Re: Size of Hole for 1 Litre/second Flow Rate?

09/16/2010 11:26 AM

We had already thought of that, drilling the hole in the top and gravity will do the rest and hopefully the sediment in the bottom will stay there.

For a rate of 1 Litre per Second we have calculated a hole of 20mm any further thoughts on this?

And I thought cats didn't like water?

Cheers!

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#9
In reply to #8

Re: Size of Hole for 1 Litre/second Flow Rate?

09/16/2010 11:37 AM

yeah, my thought is you've suddenly increased your spec' by a factor of 60!
You say 1L/m in the OP and now it's 1L/s.
I get plenty of customers like you at work.
That's what happens when you talk/write about stuff instead of doing it.
Try it, see what happens, they you'll be your own expert.
Del

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#12
In reply to #9

Re: Size of Hole for 1 Litre/second Flow Rate?

09/16/2010 11:57 AM

Relax, el gato, he's draining two different swamps.

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#13
In reply to #12

Re: Size of Hole for 1 Litre/second Flow Rate?

09/16/2010 12:09 PM

I jus hope some big ol gator bites his ass

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#10
In reply to #8

Re: Size of Hole for 1 Litre/second Flow Rate?

09/16/2010 11:52 AM

You might look here:Pipe Flow Calculation | Pipe Pressure Drop Calculation

There are lots of free flow calculators on the web.

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#15

Re: Size of Hole for 1 Litre/Minute Flow Rate?

09/16/2010 11:02 PM

Theoretically

Flow velocity V = (2gH)^0.5

Thus for 3 m head it will be 7.67 m/sec and for 4 m it will be 8.86 m/sec

Now you can calculate the hole size for 1 lit/min with these velocities.

But as Cat says in real world, the calculations do not work as we do not know perfect coefficient of discharge.. sort of hole property.

The hole diameter of around 1.6 mm will be sufficient for the required flow rate.

(With little higher coefficient of discharge the hole diameter of 2 mm may be required

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#18
In reply to #15

Re: Size of Hole for 1 Litre/Minute Flow Rate?

09/17/2010 3:34 AM

Damn, I suggested he start with a 3mm hole, never mind he can always use a KriDelTM hole reducing drill and drill it back to 2mm.
Del

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#32
In reply to #18

Re: Size of Hole for 1 Litre/Minute Flow Rate?

09/19/2010 11:37 PM
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#16

Re: Size of Hole for 1 Litre/Minute Flow Rate?

09/17/2010 12:49 AM

For storage facilities with fixed head of liquid, there are a lot of handbooks which derive a different equations which lead to find the velocity at the end of that system (point 2). One of those systems is that one attached.

And simply we can prove that the velocity at the end of the pipe shall be computed as follows:

......................................

where,

L = Length of pipe (ft)

d = Inside diameter of pipe (ft)

V = Velocity (ft /sec)

g = Gravitational constant (ft/sec2)

f = DARCY-WEISBACH friction loss coefficient [f is a function (Re * e/d)]

K = Entrance or Exit Coefficient

Z = Elevational Head (ft)

If we considered length of pipe L = 0, the equation shall be:

From which V depends mainly on elevation Z...............

And by assuming a flowrate Q = 1 Lit/min.

The hole cross-sectional area, A can be calculated as A = Q/V

And the hole diameter, D can be calculated from simple equaion of area, A = ∏ D2 / 4

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#19

Re: Size of Hole for 1 Litre/Minute Flow Rate?

09/17/2010 3:46 AM

1) Draining a lagoon would probably involve water less than clean - not easy to maintain flow.

2) Who in the world uses a ball valve for metering - a gate or globe would be better.

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#21

Re: Size of Hole for 1 Litre/Minute Flow Rate?

09/17/2010 5:30 AM

Just stick a needle valve on the end of the pipe and adjust accordingly, require more flow ? use a larger valve.

Guaranteed to work save you having to reduce the size of the hole if you overdo it.

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#24

Re: Size of Hole for 1 Litre/Minute Flow Rate?

09/17/2010 10:01 AM

Hi

At 34 feet of head and approx 15psi of pressure:

with orifice of 1/16" you will have a 0.45 USG/min Actual rate will be 92-94% percent of this value depending on drill length and shape, and water velocity over the orifice. I have based my calculations with velocity factor of approx 38'/second.

If water are containing any solids you are in trouble at this rate of drain.

Also, these calculations are theoretical and may vary

Hope it helps

Wangito.

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#28

Re: Size of Hole for 1 Litre/Minute Flow Rate?

09/17/2010 2:48 PM

You put a little tank with a ballcock so it doesn't overflow, at the bottom of your pipe. And you have a tap near the bottom of the tank. Open the tap until you get the 1 liter per minute.

The ballcock gives you constant head in the tank, the tap gives you adjustable constant flow.

If you want more accuracy that that, you can use a half 90 vee notch to measure the flow.

or you can have a rubber tube on the end of your tap. Not quite 1 lpm? Then raise or lower the end of the tube a tiny bit until it is.

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#30

Re: Size of Hole for 1 Litre/Minute Flow Rate?

09/18/2010 6:46 PM

All we need to know is how do we make a constant current source out of plumbing.

Bill

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#31
In reply to #30

Re: Size of Hole for 1 Litre/Minute Flow Rate?

09/18/2010 7:45 PM

Then just use the ballcock method. All items can be bought in a plumbing store.

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Anonymous Poster
#34

Re: Size of Hole for 1 Litre/second Flow Rate?

09/20/2010 6:05 AM

Thanks for all your help gentlemen,

The draining of the first lagoon at 1 litre per minute unsurprisingly didn't work as the 2mm hole just clogged with crud despite drilling at a location of 3 O'clock. We have asked the environmental agency if we can readdress this, probably take them a few weeks to make there minds up.

We are going to use the tried and tested technique of trial and error for the larger second lagoon. As both people on this forum and myself have suggested holes from 15-20mm we are going to start with a 10mm hole and work are way up. Would also like to thank everyone who suggested piping ideas I shall try to incorporate them to avoid turning the surrounding area into a bog.

Thanks again and Dev the cat I apologise if I caused you stress.

Paul

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Anonymous Poster
#35
In reply to #34

Re: Size of Hole for 1 Litre/second Flow Rate?

09/20/2010 6:06 AM

Del the cat even

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