Question
hi Jim,

  I'm just starting design of a system.  To start with, I'll be running off county water [70psi and 10gpm measured]but hope to drill a well in the future and switch over to a well based system then.  Main piping as well as some laterals would be underground [1" PVC], but after the zone valves, the pipe would be ON the ground serving drip emitters or micro-sprinklers.  Can i run piping, valve control wires, LV landscape lighting wires, and high voltage wires [such as to the well pump] in the same ditches?  
  The future well pump would be a submersible [1/2 horse?].  Can i run this pump without a pressure tank?  The pump would only run when the irrigation control opens a valve and turns on the pump via a pump control relay and box...then, when the cycle is complete, the controller would turn off the valves AND the pump.  It seems like this would be better for the pump as there would be no cycling.  There would be no other hydrants or hose bibs on the irrigation system.  How can i ensure that the pump will not deadhead if a zone valve fails to open?  I know I would need an in-line pressure reducing coupling at the beginning of the irrigation main, whether it was at the county mainline or the well mainline.
  I admit to being a little baffled by back flow prevention:  I know it's necessary but don't want a bunch of valves sticking up all over the yard.  wouldn't an underground check valve [same one required by the county at the water meter] serve the same purpose...I would put another one upstream from the main irrigation line cut-off valve where it tee's off the main line [underground].  Of course, when I change to a well based system, I would have to sever the connection between the new well and the county water meter and, at that time I would move this check valve to the top of the well.
  I may be WAY off base here...i hope I'm not wasting your time with stupid questions.  I am somewhat new to some of this, but not all of it.  Thanks for your time; i look forward to seeing your answer.

Dean

Answer
Hey Dean, I hope this helps. As for your first question, yes you could run all your pipes and electric in a common trench. But what I would recommend is putting any 110volt or 220 volt lines in a conduit, and burying them about 18" deep, then filling in some dirt and bury the other pipes and wire between 10 to 12 inches. As far as a pump goes, I am not real familiar with running off pumps, but any controller you buy for the sprinkling system, should have a pump start terminal that hooks up to your pump relay. The other thing you might consider, is a cistern or holding tank to draw water out of. Lets say you design a system between 8 and 10 gpm. If you run the system continuously for an hour, your going to draw about 600 gallons of water. Depending on how good your well is, you could draw down the level of your well fairly fast.If you had a holding tank, you could slowly fill this up at any time, and then run the system knowing that you had an excess supply of water to draw from. As far as a pressure reducer goes, if your only getting 70psi from the county, you shouldn't need one in the mainline to the valves. Now if you're going to be running a drip system, then you would need one, but it could be installed past the automatic valve with a filter assembly. Going back to pulling from a well, if your only running a drip or micro- spray system, you might only draw 1 to 2 gpm. and maybe you could draw directly from the well. You are correct on the backflow prevention device. Check with your county building department. Most the time you can get away with a double check valve assembly, and it can be installed below the ground in a valve box. The brand Febco also makes various backflow prevention devices. Depending on what the county requires, some of these devices need to be installed 12 to 18" above the highest output ( head, drip emmitter, etc.). But once any of these devices are installed at the beginning of your mainline, then the valves can be installed below the ground in a valve box (using an inline automatic valve). It sounds as if you're on the right track on everything you have told me. Again I wish I could be of more help on your well pump. I believe there is a blow off valve that could be installed in the mainline, just in case a valve doesn't open. I think it will open up at a certain pressure, and this line could be directed back into the well. The only other thing I would suggest, is that you don't run your drip pipe on top of the ground.  Even if you only bury them two inches, anything to keep them out of the sun will help the pipe from getting sunburned and crack, and will last alot longer. By no means are your questions stupid. It sounds as if you have already done your homework. Let me know if you have any more questions. Thanks and have a great day.