<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.
