Question
Hi Jeff, I have scanned all your "answers" trying to find an answer to my Q, didn't find what I was looking for.
My Q is about Back Pressure in an irrigation system when it's operating. As I understand it, the sprinkler heads provide back pressure on the pump and that it must somehow "balance" up with the suction pressure on the inlet side of the pump??

The problem I am having is to do with my pump failing to continue to supply water. This has been ongoing for two years now and as I have had some experience with domestic garden irrigation as an electrician in Australia, I am inclined to think that the problem is either lowering water table or a back pressure problem.

Lowering water table occurs to me because the system doesn't always fail early in summer but later in summer! However, this year it is failing earlier in summer. On the other hand, back pressure I think can be increased with manual valve in the supply line prior to any sprinkler head which I suspect may solve this problem??

I found this comment; "Too many heads is what cause the most problems" in one of your "answers"; and would like your further comments about this idea in particular.

My system has no "zones" and perhaps if I halved the sprinkler heads into two zones the back pressure would "balance" up better??
We have been in this house for 6 years and had no problem until 2.5 years ago. We are now watering on our allotted days getting 20 to 40 seconds prior to failure at a time every 15 minutes. The electrics are all AOK

Thanks for all ideas and assistance offered,

David

Answer
Probably the most effective way of solving your problem would be to install a pressure tank in the system.  This would maintain consistant pressure and would likely solve any "backpressure" issues.  I would check the system for leaks though, as even a small leak can create a loss of suction. Remember as well that the demand in gallons or liters per minute of the sprinkler system cannot exceed the pump output.  In fact it should be well below it.  Check out this link for some good information:

http://www.irrigationtutorials.com/pump.htm