[SEL] O.T. O.T. Need Help On Water Flow Problem

[Jerry Evans]

At 06:00 PM 04/06/2009, you wrote:
>Date: Wed, 3 Jun 2009 12:50:27 -0500
>From: "Elden DuRand" <edurand at mchsi.com>
>Subject: Re: [SEL] O.T. O.T. Need Help On Water Flow Problem
>Paul:
>I think what I'd do would be to use the PVC pipe as a manifold to which I 
>would attach a number of irrigation drip heads.
>
>Go to a big box store and look at the Rainbird and other systems.  You can 
>get drip heads that can be used with 1/2" NPT (I think) PVC nipples which, 
>in turn, are screwed into 1/2" NPT holes in the manifold.
>They are adjustable so you can balance the system close enough for Mother 
>Nature.
>What, me engineer??!!
>Take care - Elden
>http://www.oldengine.org/members/durand

Hi Paul,
         I'm getting into this thread a bit late but have been following 
it. It would appear that you are following plans from some "Greenie 
Magazine" :-) - have the Tomato plants read the same article ?
         I liked Ron Carolls answer as well as many others.
         If I remember correctly (I'm not going to read all the replies 
again) you have 2 main pipes going down the length (which is not very long) 
and they are closed on the ends.

         This is what I would do:

         1) I would use a slightly bigger pipe for these lengthwise pipes 
(lets just say 3/4") (it reduces friction and increases volume) (I also 
think that at the volume/pressure you are using that this will not make any 
appreciable difference to the tomato plants) and I would NOT have them 
closed at the end - I would join them (maybe with another piece of the same 
size pipe) which would in effect give you a "circuit" ie. (with no holes 
yet) the pressure would be equal throughout the circuit.
         2) Then drill your holes (but I prefer the adjustable microjet 
nozzles or Ron Carrol's idea using screws and washers). When deciding on 
the size holes (assuming you are NOT using aforementioned adjustable 
microjet nozzles) you should drill go for something like this.
         i) The "area" of the inlet pipe. (I'm going to change to metric 
here - it's easier for me to work out but the principle is exactly the 
same.) 3/4" inch pipe is (as near as dammit) 19mm pipe. (I'm also going to 
use this as an internal measurement for the sake of not letting this turn 
into an encyclopaedia).
         The mathematical formula for working out the "area" of a circle is 
"pi" X radius squared) (I do not know how to write this correctly on my 
keyboard).
         Now I'll try to explain this as easily as possible (apologies to 
all others for this "long winded explanation").
         To all you guys who understand these things I do apologise but I'm 
gonna try to explain this thing in a way that someone who does not 
understand will get the picture.
         "pi" is a mathematical formula described by some ancient Greek - 
you do not need to know how he arrived at it - just use it. Roughly it is 
(22 divided by seven) or "the answer"  (3.1428571)
         Your 19mm pipe has an internal diameter of 19mm (surprise). So the 
"area" of this opening is ("pi" X  (times) the radius) (if the diameter is 
19 mm then the radius is half of that or 9.5 mm
         This equals pi (22 divided by seven) or 3.1428571) multiplied by 
the radius of the 19mm pipe
         3.1428571 x 9.5(the radius - or 1/2 of the diameter of the pipe) 
equals 29.857 (unless my cheap Taiwanese calculator is lying to me). This 
is the delivery area of your pipe. 29.857
         Now divide this by the number of "delivery points" that you need. 
In your case you mentioned 16 (tomato plants). So divide the answer above 
by 16 - ie. 29.857 divided by 16 = 1.8660625. and this will give you your 
answer for the area of the holes you need. Now you need to convert this 
"area" back to a diameter (so you know what size drill to use). Now, for 
tonight, I've forgotten the formula  needed here so I will use "Google" (to 
work out the "diameter of a circle" from the area").
         This gave me an answer of "1.5414099285872527" - If "Google" was 
correct then you need to drill all your holes "1.5 mm".
         What I would do is to drill these holes approximately half of this 
size and put a bucket under any one of the holes and measure how long it 
takes to provide your required amount of water (always trying to bear in 
mind that the tomato plants have read the same article.) It's more accurate 
to have "half size" holes and leave the tap (faucet) open for twice as long.
         Sometimes "maths" or "science" can baffle us all - have the tomato 
plants also read this article?
         Now, the above method will only work if your delivery (where the 
water comes from) pressure is always exactly the same. Do you really think 
that the tomato plants give a damn?

Understand that this answer will only be relevant if your water pressure is 
always exactly the same ie. "all things being equal".

         Paul, I've been there, done that and bought the "t"shirt. Fresh 
"homegrown" veggies are really great and they are also "so green". But, at 
the end of the day, they will always cost you more than you can buy them 
for at the local vegetable shop. The reason is that you will grow veggies 
"in season" at the same time as the "big producers" put theirs on the 
market. Unless you are planning to produce "out of season" (which involves 
major investment in greenhouses and similar) you will not win financially.
         Just my opinion. Be prepared to have that "They came from my 
garden" expression cost you Bucks.
Jerry

Keep the revs up (or down)
Jerry Evans
Near Johannesburg in Sunny South Africa.
Etched Brass Engine Plates made to order:
<www.oldengine.org/members/evans/plates/index.htm>