SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

Thanks for the info.

Hi, It has been a while and I have been busy setting up my system. I have learned friction loss is not as big a deal in drip irrigation (as Dr. Pete pointed out earlier) since you must reduce pressure to keep from popping off the emitters from the main and sublines. I'm not real sure the guy who took me to task on my naive pressure statement above really knows too much about drip irrigation. I think he is a sprinkler guy where friction is a big concern.

Altitude from the water source I think has more of an impact on pressure variation in low pressure drip. As far as distance check out the link above at Nebraska it addresses many of these questions. The length you can run is much much longer even if you go up another 1/4" in diameter say from 1/2" to 3/4" the carrying capacity of the system dramatically increases from 150 ft to well over 300.

Take Care, Dripman

I have installed a few drip systems and found that the Rainbird xerigation control zone kit works very good. It is designed for drip systems and includes the recommended filter(very important).

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">if you turn the water on on a hose no matter what length it is - it has to come out (at the same pressure) at the other end. So unless you are using many emitters (drippers) on the line, the pressure is the same at both ends.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

It sounds like this comment may have already been discussed via emails, but just in case, I figured I'd discuss this in the forum.

These statements are false, mainly about the pressure being the same at both ends of the hose.
The pressure will only be the same at both ends of the pipe if no water is flowing. Once you start making the water flow, there will be friction losses as the water "rubs" against the side of the hose. This friction loss results in a drop in water pressure along the length of the hose.

So the bottom line reason you will see "rules" of drip irrigation design say something like "no more that 200' of hose and no more than 150pgh of emmiters per circut" is to make sure these friction losses stay low enough that you don't have a huge difference in pressure from the first emmiter to the last emmiter.

You will get different "rules" from different sources because they are all trying to find simple ways to explain how to build a drip irrigation system without forcing you earn an engineering degree in fluid dynamics.

dripman, you never mentioned what brand of drip you are laying down. What type is it? And what is your psi and flow at point of connection?

any time .... glad we could help!

Ray and Dr Pete,
I appreciate the information. Just in case someone else is inclined to do drip irrigation check out this link http://ianrpubs.unl.edu/irrigation/g525.htm It is a University of Nebraska release that pretty well answers most questions about pressure and system capacity. Not much on specific product brands and pipe friction. That's where you guys were a big help. Thanks!! John

For the runs with the emmitters you only have 15 psi in the lines, so yeah its overkill....as far as your main lines to your valves, you cannot use poly because once poly is put under pressure it POPS!! As far as the valves and the controller those are the best ones on the market today so definatly use them!

Pete,
The table was very helpful on friction's effect on water flow, I appreciate you sending the link.

Still waiting to hear back from Ray on solving my problem and answering my pipe question on 'is 160 PSI poly really needed'. I'm going with the valve and controller products Ray recommended unless another expert has a recommendation.
Thanks again

The reason for the loss is due to friction of the fluid passing through the pipe. I think with drip irrigation this is probably negligable due to thefact that you wont be pushing 10 gallons per min through the 1/2" pipe. The fricion becomes a problem as the distance increses and as the diameter of the pipe decreases. See this link for further info http://www.sprinklerwarehouse.com/LawnCare/frctn_ls.pdf