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Troubleshooting Old Residential System

Discussion in 'Irrigation' started by kellanv, Feb 28, 2014.

  1. kellanv

    kellanv LawnSite Bronze Member
    Messages: 1,147

    Howdy folks,

    I ran into a situation today that I could use some input on. Last week I was called to client's property to take a look at their system. The zones were broken up into 4-5 rotors per valve (varying types, nozzles etc due to haphazard replacement). When the zones ran, they were dribbling out with no pressure. Static pressure was 54 psi at the bottom of the hill. PRV was wide open, with 92psi at the street so we had a plumber replace it and had it set for 75psi as per his recommendation.

    Now, the rotors are a lot better/closer to their correct radii but I'm only getting around 16-20psi using a pitot tube at the nozzle.The spray zones I'm getting a bit less. They are both still throwing a bit short.

    I'm starting to wonder if there isnt another issue going on. I did a bucket test at the hose bib and got 3.5 GPM which seemed pretty low.

    Meter is 5/8"
    3/4" copper line to house (from what I could see leaving the meter/entering the PRV)
    1" PVC irrigation main line
    1" DCA

    Is this just a case of a lot of dynamic loss? My thought is to switch to MPs everywhere to drop the flow but I dont want to repair by replacement if its something bigger.

  2. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,246

    If the backflow preventer is a DCVA (make and model number?) with testcocks and isolation valves, when was the last time it got a proper inspection?
  3. 1idejim

    1idejim LawnSite Fanatic
    Messages: 11,094

    I get 52-54 psi after meter-prv-dcva so that's in line. You say "at the bottom of the hill" so what's your rise/run?
    What was your demand before R&R of the heads? What's your current nozzle demand?

    Again you have to answer what the demand is?

    You're getting 3.5 gpm at what pressure, gpm without a dynamic pressure measurement doesn't tell you much? What is your static at the same bib?

    It sounds as if you have two separate issues to work through.

    1) you seem to be losing 50+/-psi between the meter and the nozzle.
    2) the meter should have no problem supplying 20gpm yet you're measuring 3.5 at the HB.

    I would tap and install a HB at the bottom of the hill for the comparison test. Once you have a dynamic measurement of the supply just after the prv&dcva you'll have more of an idea of what's going on under the ground.
    Posted via Mobile Device
  4. kellanv

    kellanv LawnSite Bronze Member
    Messages: 1,147

    Few more details:

    Basically, in text diagram form:

    Meter --2' 3/4 copper --> 3/4" PRV --~30' 3/4 copper--> irrigation tap (1"PVC) --5' 1" PVC-->1"DVCA-->zone valves. There is probably another 70' of 3/4" mainline between the irrigation tap and the bib at the house.

    Hose bib is on the house supply, not through the DCVA.That is where I tested it previously at 52 PSI. There is a ~20' (possibly a bit more) drop from street to where I measured 75 static on the hose bib after the repair. PRV is 2' from the meter at the street, so likely is outputting somewhere around 66 psi, then increasing to 75 at the bib due to elevation.

    Each rotor zone is setup for ~3.6-5 gpm

    DVCA was partially buried so only got the size. Ill get that information when I go back. Probably hasnt been tested in many years as most aren't here unless broken. I do not have my BPAT license yet but I should have it soon so I can test/repair legally.

    I didnt have a dynamic pressure setup for the hose bib so I will likely build one then return to see what I can do there.

    I was thinking that I might be able to do a dynamic pressure test after the DVCA to see if the issue is between the irrigation tap and the meter or something later on.

    That being said, when I do the dynamic test and adjust for say 30psi at the bib, that flow rate would be less than 3.5 considering that was wide open, correct?
  5. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,246

    Allow for the likelihood that the system will be non-functional until the DCVA is dealt with.
  6. Without A Drought

    Without A Drought LawnSite Bronze Member
    Messages: 1,084

    sounds like you're over zoned. Like the original installer did a bucket test for GPM without having a dynamic pressure reading (a la wide open). he then sized the system based on that reading (your zone demand and GPM reading are pretty close).

    like jim said get a dynamic reading, test the DC and rule out any other possible restrictions. if you do that to no avail, you have the choice of nozzling down or splitting the zones or eliminating heads or other options.
  7. ArTurf

    ArTurf LawnSite Platinum Member
    Male, from Ark
    Messages: 4,257

    Can the customerr tell if the system ever performed properly (I know, most of the time they can't)?

    Is there a shut off valve after the tap for irrigation? Maybe this valve is not open all the way or faulty. One time I had a similiar situation and found a gate valve the customer never knew about. The valve had failed and the gate was only half open.
  8. 1idejim

    1idejim LawnSite Fanatic
    Messages: 11,094

    Bingo. There seems to be two successful ways of finding the source of any problem. One is to qualify yourself to run the proper tests and the other is to hire someone more qualified to test it for you.

    Varying test results within a system really speak loudly.
    Posted via Mobile Device
  9. kellanv

    kellanv LawnSite Bronze Member
    Messages: 1,147

    Will do. Hose bib flow rate of 3.5 should not have been affected however.

    Apparently I am the 4th irrigator to try to figure this out so no, it likely hasn't been working well in recent years.

    I believe I have done most of them but I am obviously still learning. I'm trying not to half-ass and actually learn how to troubleshoot these sorts of things which is the reason I asked here. I have not seen such a disparity between static/dynamic before. I found the bad PRV as part of my investigation so at least I'm making progress.
  10. kellanv

    kellanv LawnSite Bronze Member
    Messages: 1,147

    Oh, and I checked all the shutoffs in between POC and the remote valves. Nothing seemed askew and all operated.

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