PGP "Leakage" When Adjusting Radius

Discussion in 'Irrigation / Sprinkler Forum' started by vivona, Sep 1, 2010.

  1. vivona

    vivona New Member

    My lawn spray company told me I needed to replace my Hunter PGP 4" rotors because they were leaking. Indeed, there was water trickling down the side of the riser section on several of the rotors. I went ahead and replaced all seven since they were 8 years old. When adjusting the new PGP rotors to reduce the radius of the spray, I noticed that as soon as the screw contacts the water stream, water begins to trickle down from the nozzle. It appears that the "leak" was not a leak at all, but simply a characteristic of water hitting the radius adjustment screw. In fact, the only old rotors that were leaking were the ones that had the adjusting screw in the water stream, so my old rotors were not really leaking after all.

    I do need to reduce the throw of several of my PGP rotors, but the water trickle does flood the area around the head leaving the ground soggy afterwards. Is there any other way to reduce the radius of a PGP rotor without going to a smaller sized nozzle? Do the low angle nozzles really make that much of a difference in stream radius?
  2. Fireguy97

    Fireguy97 Irrigation Contractor

    That's what happens when the screw hits the stream.

    To answer you first question, No. If you have to shorten the stream that much, you need a smaller head in those spots, not PGP's.

    Low angle nozzles will drop the height of the stream, not so much the radius.

    What is the coverage distance that you are looking for? Do you know what your head pressure is? Depending on the pressure that you are working with, your distances will be from 22' to 50'. If you require a shorter coverage area, you will have to install a smaller (shorter distance) head.

  3. vivona

    vivona New Member

    I do not know what the head pressure is. This is an existing system I had installed eight years ago and I have simply changed out the rotors, which were all PGP units. Two of the PGP rotors were set at 23 feet to fit the intended area and to keep from hitting the house. They both had a Red #7 nozzle cranked down with the stream adjustment screw to get the 23 foot radius. That created a lot of splash at the nozzle and I am trying to reduce that.

    I have printed out the nozzle performance data for the PGJ and PGP series. The new PGP rotors came with the Blue series of nozzles with the Blue #4 nozzle pre-installed. The Red #7 used previously used about 3.4 gallons, and with 7 units the zone consumed about 24 GPM. So, I already see that I probably need to change out some or all of the nozzles because the 7 new units are using 28 GPM.

    I have created a spreadsheet that calculates the inches of precipitation per minute for each head and see that the original system was all over the place. In fact, before changing the heads I had set out pans to measure coverage and the results were very varied, with some areas getting four times the water as others. I also drew up the spray patterns and see that some areas had four sprinklers hitting them.

    I am currently trying to balance out the system and by adjusting the patterns and nozzles of each head, and adding one head in an area that only was served by one, I think I can get the coverage much more smoothly distributed. But... unless I tear out and start from scratch (don't wanna do that) I need two of the heads to fit a 23 ft radius. I did check the chart on the smaller PGJ head and to get a 23 ft radius without using the adjusting screw, I have to use a 1.5 GPM nozzle. A low angle nozzle on a PGP doesn't give me much more GPM, since I would have to use the Gray #4 nozzle and would only get 1.75 GPM. I suppose I could drop the GPM of the entire zone to match and increase run times to make up for it.

    So, unless there is a different brand or model of rotor that gives the GPM I need, but keeps the water in a smaller radius, it looks like I have to crank down the adjustment screws on those heads and live with the soggy area around the heads. Or, I could look at dropping the GPM output of the zone so I can use the smaller nozzles.

    Any recommendations?
  4. Fireguy97

    Fireguy97 Irrigation Contractor

    It looks like you have a mess. Common industry practice dictates that all water is projected away from a home or building. From the sounds of it, the person that installed the system put the pipes in the wrong spot. The heads should have been installed so that they spray away from your home.

    You are doing right by trying to balance the heads for even output. That is another thing that should have been done from the start. Hopefully you don't live in an area that is charging you for every drop of water.

    The difficult part is that I don't know what your layout is, and I don't know what heads you have facing hour home, and if heads are on the same zone that are in other spots. It almost sounds like you really should start over to do it properly, and to separate the heads into zones that can be balanced easier.

    From your description, you have some heads that you are dialing down that are hitting your home, and some other heads that are on the same zone that are spraying free. With this design, you will always have problems, because you will never be able to balance the zone properly.

    I can't recommend anything without at least knowing what your water pressure is, and what your flow rate is. For water pressure you will have to place a pressure gauge on a hose bibb near or attached to your irrigation system. For flow rate, if you don't have a gauge, the easiest way is to time how long it takes to fill a 5 gallon bucket.

    I'll also need to find out how many heads are on your zones.

  5. vivona

    vivona New Member

    Thanks, Mick, for your thoughtful reply. Yep, I am using city water and pay for every drop.

    The irrigation system tees off from my city water meter. I cannot easily measure the pressure or GPM going into the irrigation system, so I measured at the hose bib at my house’s water supply line. The pressure was 60 PSI with no water flow and 50 PSI with the irrigation system running. The specs say I am losing about 7 PSI through my Wilkins 950XLT backflow preventer. I don’t have a gauge that I can fit to a sprayhead, so I don’t know what the PSI is by the time it gets to the sprayheads.

    I measured the main supply capacity at 16GPM.

    To clarify, I am only dealing with one zone of my 6 zone system. That zone had 7 PGP rotors that covered the entire back yard with a little help from the shrub heads along the back of the house which are on another zone. I have added one PGJ rotor because there was an area only covered by one sprinker. So, I now have 8 rotor heads on that zone. Even if I assume that the irrigation system is running at 30PSI, the original configuration of this zone would need 17.6GPM, so it was running at less than that. I need to redesign the zone to use less than 16GPM and adjust the run times accordingly.

    I made a drawing of the system, but the overlaps do not show well so I am reworking the drawing and will post it later.
  6. vivona

    vivona New Member

    I have completed my first try at tweaking the sprinkler head types, nozzles, and layout to get the system down to below 16GPM and improve distribution. I haven't measured actual pressures at each sprayhead, so I am assuming (for now) the pressures listed in the table below the graphic. The system is fed starting at head #1 but I don't know the piping layout. Once I get a pressure gauge rigged to measure sprayheads, I can adjust accordingly.

    The original setup had rotor heads #1 through #7, all PGP's with Red-7 nozzles, most cranked down with the radius adjustment. With the installed nozzles that original system would have needed more GPM than available, so I don't know what the actual distribution was. All I know is the irrigated part of the back yard is 3100 sq ft and at 16GPM it would have taken 90 minutes to get .75" of water over that area assuming even distribution. The installer set that zone to 50 minutes, so I was only putting about .42 inches of water down overall, with some areas getting less than half of that. It is no wonder half of the lawn kept dying.

    My diagram shows the setup after my planned changes. Any area shown with a pebbled texture is a shrubbery area. The two brown squares are a shed and patio. What I plan to do is move heads #2 and #5 each two feet closer to the back fence and change them out for PGJ's with minor radius reductions, then add head #8, a PGP, to provide overlap for sprinkler #7. All heads get smaller nozzles than the original setup had. The lawn areas near the shrubbery around the back of the house do get coverage from shrub nozzles which are not shown on the diagram. Since head precipitation charts assume proper head layouts, I had to compute coverage by measuring the GPM and sq ft of each head. I then looked at the coverage diagram and added up the inches per minute for each area based on how many heads were hitting that area and the inches per minute of each of those heads. The distribution runs from .006 to .009 inches per minute for most areas, with a few hot spots getting up to .014.

    My planned changes should vastly improve the distribution though it is far from ideal. Other than dig up the system and start over, I don't know how to make it better. I welcome your input on my proposed system changes. I haven't started digging or bought parts yet, so feel free to suggest any level of changes.

    By the way, after quotes for replacing the dead sod (front yard has issues too, but I am not working on that yet) versus replacing the entire lawn, I have decided to stop fighting Floratam turf and have ordered a new Empire Zoysia lawn which is claimed to be a better grass for Central Florida (more drought and chinch bug resistant) so I have about a week to dig and change the irrigation system before the new grass gets put down.

    Sorry for the quality of the graphic. I did my drawing in MS Word and had to do a screen capture to get it as a graphic file. Each head is where the # is shown on the diagram. Head #4 (yellow) is the hardest to see the pattern for because it is blocked by others. It's pattern is close to a half circle which extends all the way to the shrubbery in the top right corner. Head #2 is shown in red with most of its half circle pattern covered by head #1.

    Back Yard Sprinkler Chart-New Rotors & Config.jpg
    Last edited: Sep 15, 2010
  7. Fireguy97

    Fireguy97 Irrigation Contractor

    I only have a minute to look at this, but it's easier with a diagram. What are the grey/brown areas outside of the sunroom and at the top right? Could you move #6 the the outside of that area, to the inside corner?

    Have you taken into consideration that #2 and #5 360's will take twice the time to run their coverage areas as the 180 at #4, and four times as much as the 90' at 1,3, 6, and 7?

    How many zones is this?

    You do realize that head-to-head coverage is what you shoud be going for. I do know that with this lawn it'll be very difficult to do that.

    Would there be any way of adding a head (at the hump below #5) in the future?

    Last edited: Sep 5, 2010
  8. vivona

    vivona New Member

    All of the irrigation heads shown on the diagram are on the same zone.

    The grey/brown pebble-textured area outside the sunroom is landscaped with a patio immediately to the right of the sunroom and shrubs/mulch in all other areas. This shrub area is served by sprayheads on another zone. Those sprayheads do extend their pattern for about 8 feet out from the shrub area so there is some help filling in the lack of coverage in the lawn rotor zone.

    The pebble-textured area in the top right corner is another shrub/mulch area. It doesn't have its own sprayheads other than #6 and depends on the lawn rotors for additional coverage. That is why I cannot move #6 out of the area, though I have considered moving it diagonally out some from the corner some, perhaps 4 or 5 feet.

    Head #2 is a 180, so #5 is the only 360. My calculation spreadsheet takes into consideration size of the area covered, so a 90 degree rotor only needs 1/4 the GPM as a 360 to get the same inches of of precipitation. Or, with the same GPM a 360 rotor will need four times the run time as the 90. The only other consideration would be if the rotors ran so slowly that on the last rotation the 90 completed three sweeps while the 360 only made it 3/4 the way through its pattern. With this zone having to run at least 90 minutes, I am figuring that all heads will make enough rotations through their pattern to make rotation less of a consideration. I need to measure the rotor speed to see how long a full turn takes and see how that plays out.

    As I see it for head-to-head coverage:

    #1 gets coverage from the shrub nozzle in the shrub/mulch area to its right.
    #2 is covered by #1, #3 and #4.
    #3 is covered by #2 and #4.
    #4 is covered by #3.
    #5 is covered by #4.
    #7 and #8 cover each other.

    That leaves #6 as the only one not getting coverage and it is in a shrub area and hard to get coverage to.

    Interesting idea to add a head at the hump below #5. With 8 heads on one zone and 17 GPM to work with, it may not be possible to add another head, particularly since I have found the piping serving #7 and #8 to be 1/2 inch PVC. I will look at at moving #8 near that area and extending its radius and expanding its pattern to 180. That might allow me to reduce the 360 pattern of #5.
    Last edited: Sep 6, 2010
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