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Pressure Loss Question

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m7317

Active Member

Posts: 11

1

Friday, April 9th 2004, 3:15pm

Pressure Loss Question

Is there a major pressure loss when you have a barbed 90 or tee in a zone, or any kind of 90 or tee?!? Example: If i come off the first head with a tee and goto another head on the left and 2 on the right.


Example: H------H--------H
| |
| |
| H
|
Valve Manifold
Thanks.

HooKooDooKu

Supreme Member

Posts: 685

2

Tuesday, April 13th 2004, 6:46am

I don't fully understand your example, but I can tell you that there are charts that will indicate pressure losses through various fittings. It's usually expressed as an equivilent number of feet of pipe.

As an example, I think a typical 90 elbow is equal to adding an additional 1 foot of pipe. You'd have to find charts for the pipe you are using (for the real answer might be something like 3ft).

m7317

Active Member

Posts: 11

3

Tuesday, April 13th 2004, 2:04pm

I have found tables, but i'm not sure if i understand them correctly. Example, say you loose 2 psi for every 100 feet of pvc pipe, would the pressure loss for a pvc 90 be something like (2/100=.02psi assuming that a 90 is equal too 1 foot of pvc pipe)?!? Am i understanding this correctly?!?

HooKooDooKu

Supreme Member

Posts: 685

4

Thursday, April 15th 2004, 12:43pm

Yes, that's how I understand the tables/charts to work. The charts for the fittings indicate what the equivilent in feet for a fitting, then you use the pressure loss for the type pipe you are using.

So as an example, let's assume that for a given gpm, the tables tell you that a 90 elbow = 2ft and pressure loss is 5psi/100'.

You run a pipe across the front yard for a distance of 50', then you turn 90 to the right and go strait for 10', then you turn 90 to the left and go strait for a distance of 5' (your trying to go around an obstical), then you turn left for another 90 and go back 10', then turn 90 to the right (so that you are back on your previous course). You then have to go another 40' to reach where ever you are trying to go.

Total distance is 50 + 2 + 10 + 2 + 5 + 2 + 10 + 2 + 40 = 123ft

123ft * 5psi/100ft = 6.15psi pressure loss.

m7317

Active Member

Posts: 11

5

Friday, April 16th 2004, 11:59am

Excellent, that is the way I understand the fittings charts. If you can help, I got one more questions reguarding pressure. Is it better to connect all the heads in one run of poly pipe, or is it better to split the zone up with a tee into two halfs?!? Meaning, if i have six heads in a zone, should they all be connect in one run after the valve, or should they be split into two, three head sections after the valve?!?

HooKooDooKu

Supreme Member

Posts: 685

6

Friday, April 16th 2004, 6:54pm

The best answer is that you want the pipe to be as short as possible from the valve to each head. Of course to accomplish that, you'd might have to run 6 pipes strait from the valve to the heads.

So the comprimise is to run as many tees as needed so that the total pipe used is minimized. (i.e. the pipe should be in H and T shapes, Not S shapes.
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