Heads have Low Flow, Pressure, Throw Distance (not sure which is correct term!)

Hello,

I've been a lurker on here for a little while, and decided it was time to register and just throw my question out there. I sure can't figure it out on my own, and figure the kind pros on here might take a stab at it! Thanks so much in advance, if you do. I really appreciate the amazing wealth of knowledge that is made up of all you regular posters on here.

Going by the subject line, you can see I have an issue with the heads in my system reaching the originally planned radius of throw. The system is original with the first owners of the house, from 1993. A few heads have been replaced over the years, including 2 by me (one each of the last 2 years). 1" main poly pipes for each zone and 3/4" outlet threads at each sprinkler head location. 3 zones, 5 heads on each. Most are really old Rainbird and there have been a few Orbit/Hunter replacements. Since I've moved in 4 years ago (and I can't put my finger exactly on when) I noticed the throw is just not where it used to be. These heads that claim 30-50 feet are doing maybe 20 or 15 in some cases! The streams of water that used to be nice fanned "rain curtains" are now just streams even when I adjust the mini screw for that. So that tells me the pressure is low, but also that the volumetric flow rate is low? I'm not sure what to check. I've taken various heads off, on the low ends of each zone, thinking that's where debris might be, and i've never found anything significant. Even if that was the case, wouldn't only one head (the lowest altitude one) show blockage behavior and the rest would throw even farther since one on the zone was blocked? That isn't happening.

In short, it seems like a system-wide issue, and not individual heads or zones. My well pump is set for the 50-65psi cut-on/cutoff range, but I can't say what the pressure is at each sprinkler location. When I put adapters on a garden hose and put heads onto it, the throw seems correct, so I get plenty of flow/pressure out of a hose spigot. So it's not the heads themselves.

What can I check besides digging up every single head and letting things flow for a while (in which case, how on earth do I prevent an even worse infiltration of dirt and mud going back into the system while they're off? Do one at a time? Wouldn't that allow me to miss debris, if there was any?)

Does the age of the system indicate I could have problems at the manifold and in each of the valves? Pretty much the same degree of problem on each of the valves would be possible? I'm not even sure where that stuff is, as there was no literature left, and I'm hesitant to just start digging as I don't know exactly what the shape is and where there might be loose wiring that I would cut into. I imagine this underground stuff is near the outside Febco main valve right off the house. My water is fairly rusty, and I have Manganese and Calcium at probably an average level. Is there a way to "blow out" debris in valves without blowing up the whole system? Speaking of, the only other thing that crosses my mind is leaks in the main lines? How would I ever identify where those would be, since the line is a good 12" down in most cases? I blow my system out myself each year, with a homeowner compressor at about 40 to 50 psi, which I'm told is still in the safe zone, knowing air is way more viscous than water and could rip stuff apart if I wasn't careful.

I know, lots of questions, and lots of detail, but I wanted to answer anything I could think of that might be relevant here, before anyone takes a stab at a reply. If I failed to mention something that is key, please let me know. I don't have pressure or volume readers/gages, although I could somehow measure flow/hour with 5 gallon buckets, I suppose.

Where would someone look first in this case, knowing what I've already tried?
Thanks much, in advance!

Just a quickie as I have not yet made coffee. Get a water pressure gauge, about 0 to 80+ lbs and put a female thread coupling on it. Take a sprinkler head off and put on the gauge and see what is what. Is there a water filter between the Febco valve and your irrigation line. If there is, good chance it is clogged.

I would get a pressure and flow reading at the hose bibb where you blow out from. See what the pressure and flow is from that hose bibb. Those rates will be what the system uses. You can compare that to what you get at the heads, but expect a drop by several pounds by the time that water reaches the heads.

Water pressure may have come down over the years in your neighborhood, Talk to you local water department to find out what kind of pressures that you 'should' be getting at your home. They will tell you what the municipal pressure is.

You could have a faulty Pressure Reducing Valve (PRV). When the PRV fails, you will get a huge pressure drop in your home. If there is a big difference in municipal pressure and what you are getting at your hose bibb, I would look at your PRV.

You also could have damaged your pipes (by freezing) by using a homeowner compresser. When I blow out I only use 55 lbs., but I have an unlimited supply of air at that pressure. Normally small compressures don't have the volume of air to push out a water colume that big in one shot. A small compresser will have to blow out a zone multiple times, and still not get all of the water out. The water will find a level, and have water in the lower part of the pipe. A small compresser will have enough pressure to create an air gap at the top of the pipe, and the rest of the water might not come out properly.

Mick