Huge pressure drop with 1 sprinkler

Discussion in 'Irrigation / Sprinkler Forum' started by h22lude, Aug 30, 2020.

  1. h22lude

    h22lude Member

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    I'm using a Hunter Pro-Spray (non regulated) body as an above ground sprinkler. At my spigot (3/4" pex), I get 70psi. If I connect a 6ft 5/8" hose with 1 spinkler, I'm getting 30psi. How can that be? That seems like an awful lot of pressure drop
     
  2. WorthFlorida

    WorthFlorida The wife is still training me.

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    Is this 6' hose by chance a washing machine hose? How are you taking the reading and where? What type of sprinkler?

    When water is not flowing the pressure will be the same everywhere. As the water flows is when pressure will drop. The faster the water flows the lower the pressure will be. The same as an aircraft wing. Air flowing over the top is faster causing air pressure to drop, therefore the higher pressure under the wing pushes up and causes lift. Washing machine hoses may have a filter screen at the faucet connection.
     
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  4. h22lude

    h22lude Member

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    No the hose is a regular cheapo garden hose. Readings were taken with a Rain Bird spigot pressure gauge. At the spigot was about 65psi. At the sprinkler with it running was about 35psi.

    The sprinkler is a Hunter MP Rotator MP3000 90°. I made a 3/4" PVC stand for it.
     
  5. Reach4

    Reach4 Well-Known Member

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    Can you measure the pressure at the spigot while the sprinkler runs?

    Can you measure the pressure at the other spigot, or at the drain on the water heater, while the sprinkler runs? The point is to find out where the pressure drop occurs.
     
  6. WorthFlorida

    WorthFlorida The wife is still training me.

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    I wouldn't worry about the pressure. I've used those MP rotors and they have a lot of built in restriction and don't expect a whole lot of water from them as they are designed for a low volume watering. The spec on these do state that the watering times need to be increased from a standard pop up spray head because of the low volume of water. Its designed to minimize runoff and overspray by giving time for the water to soak into the ground.
     
  7. Reach4

    Reach4 Well-Known Member

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    Low volume would seem to be a good reason to troubleshoot why 65 psi dropped to 35 psi.

    Maybe h22lude has a clogged cartridge filter that feeds not only the house but the hose spigots.
     
  8. h22lude

    h22lude Member

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    I just did some more measurements. Not sure what to think.

    Testing the backyard spigot. This is the one I just replaced the spigot and PEX tubing from 1/2" to 3/4". Tested at the spigot I got 80psi (I have a 40-60 switch so I'm not sure how that is possible). Adding one sprinkler, the pressure is 50psi. Adding a second, I got 30psi.

    Testing the front spigot, which is a longer run of PEX and it is 1/2" PEX. At the spigot I got 60psi. Adding one sprinkler I got 50psi. Adding another sprinkler I got 30psi.

    With the meter on the front spigot, I was right about 60psi. If I turn two sprinklers on in the back (inline) the front spigot went down to 40psi.

    I was hoping to run 4 MP Rotators on one spigot. Doesn't seem like I can. Not sure why. If I got inground sprinklers, I would probably need 50 zones with 2 heads each. This seems really bad to me.
     
  9. Reach4

    Reach4 Well-Known Member

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    If that spigot is 46 feet lower, that could explain a 20 psi difference.

    I infer you have a well. Does the pipe to your backyard spigot tee off between the house and the well, or does the backyard spigot water go through the house?

    Where are you reading the pressure? At the spigot, or at the pressure gauge at the pressure tank?
     
  10. wwhitney

    wwhitney Active Member

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    +1. And if you have a 20 psi difference in static pressures, while no water is running, and you don't have a 46' elevation difference, then something is wrong with your pressure measurements, or you have a pressure reducing valve somewhere in there.

    A simple diagram show the locations of the spigot, pipe sizes and lengths, and source of water would be helpful.

    Cheers, Wayne
     
  11. h22lude

    h22lude Member

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    46ft lower, as in a 46ft longer PEX run? The length of the piping difference is probably 20ft. Height wise, they are roughly the same height off the ground.

    Yes, on a well. They both tee off right after the pressure tank. 3/4" PEX goes after two big blue filters (this issue was happening before the filters were installed), the front spigot tees off pretty much right after the filters. The back spigot tees off going to the water heater which isn't far from the pressure tank in the basement.

    The readings I posted are at the spigot using a Rain Bird gauge
     
  12. h22lude

    h22lude Member

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    Just about to head out but I can look into doing a diagram tomorrow.

    Wouldn't a longer run of smaller ID PEX cause the static pressure drop?
     
  13. Reach4

    Reach4 Well-Known Member

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    We meant altitude.

    Also look at the pressure at the pressure tank.
    1. This will give pressures before the filters. This is important measurements while the water is flowing.
    2. When no water is flowing, this compares the calibration of the gauges.

    Feeding lawn sprinklers via whole-house cartridge filters is unusual.

    For your studies, putting a garden hose thread pressure gauge on an indoor laundry tap or drain for the water heater should be a good measure of how much pressure drop occurs in the filters while you water the lawn. Compare with pressure at the pressure tank (before filters).

    You could also put your garden hose thread gauge on the drain valve at the bottom of your pressure tank. That would be good for comparing pressure gauges.
    Not at all. At that point (no flow), any differences are due to altitude.
     
    Last edited: Sep 5, 2020
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  14. wwhitney

    wwhitney Active Member

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    Ah, that accounts for the 60 psi versus 80 psi pressure reading. Presumably your pressure switch is set at 60/80? So one static reading was just after the pump had cut out, and the pressure tank was at 80 psi; the other reading would have been just before the pump was about to turn on, when the pressure tank pressure had dropped to 60 psi.
    No, in a static system (no flow), pipes don't cause pressure loss, only elevation does. When water is flowing through a pipe, there is frictional pressure loss, which depends on the flow rate and on the pipe diameter.

    Cheers, Wayne
     
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  15. wwhitney

    wwhitney Active Member

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    So, I've not considered a well source before, but I would think irrigation design would go like this:

    - Figure out how many how heads you'd like to run at once. For each head, look up the design pressure requirement and flow at that pressure.
    - If the well pressure switch is set at 60/80, then use 60 psi as your design available pressure. [Not sure about this, not so familiar with wells, but it should be conservative.]
    - Verify your well and pump can provide the required flow at 60 psi indefinitely. [Otherwise, reduce heads/flow.]
    - The difference between 60 psi and the sprinkler head design pressure is your available pressure "budget". That budget goes to (a) elevation difference between the heads and the pressure tank and (b) frictional losses on the piping from the pressure tank to the heads. If your actual frictional losses exceed your budget, then either reduce heads/flow, or enlarge pipes.

    Your procedure with the hose bibb lets you measure the frictional loss your existing piping is causing, with the caveat that the hose bibb and hose are causing some pressure loss that a permanently installed system wouldn't have (particularly the hose bibb, I would think, they have pretty small internal orifices). Not sure how big an effect this is.

    I assume you are using a wye at a spigot, with the pressure gauge on one side and the test sprinkler on the other side? Then the data you really want to capture, at some instant in time, is (A) the flow rate out of the sprinkler (B) the pressure at the spigot and (C ) the pressure at the well tank. The difference C - B is the pressure drop of your piping to the spigot (+/- elevation correction) and A vs (corrected) C - B characterizes your existing piping. The bigger the pipes, the smaller the (corrected) C - B for a given A.

    [If it is difficult to capture both C and B simultaneously, then there are way to infer C. For example, if you note B and turn off the spigot really quickly and then immediately note the pressure reading, that is approximately C (along with the correction for elevation difference, which is good). I say approximately because if the well pump is running, the gauge should be moving up to 80 psi (+/- elevation correction), so it will have changed somewhat while you were turning the spigot off.]

    BTW, drawing water at one hose bibb while measuring pressure at another isn't a useful procedure for a well fed system. For a city water fed system, measuring at a hose bibb right where the water lateral comes in plays the role of measuring at the pressure tank in your system.

    [Edit: second everything Reach4 said about filters, I hadn't considered those.]

    Cheers, Wayne
     
  16. WorthFlorida

    WorthFlorida The wife is still training me.

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    As I stated before, I think you are getting to much into the pressure thing. When your well pump kicks on, the pressure tank will take a some of the pressure. The pump is providing for the pressure tank, the irrigation system and any domestic water being used. With a city water connection it may barely be noticed but with a well system there is a limit. Connect up the number of sprinklers you want and give it a try. If the distant covered by one sprinkler is to your satisfaction then go with that number. What size pump do you have? WWHITNEY has very good suggests to follow.

    If this is a well for domestic water, a CSV valve may be a good option for continuous water pressure. https://cyclestopvalves.com/ and it will also save your pump. It was design by a moderator on this forum the "valveman". He has thousands of post.

    If the pipe from the pressure tank is 3/4", use that size to feed the zones or increase it to 1", all depending on the size and type of irrigation system. To connect the sprinkler use a tee, and tee off with 1/2 " pipe and make the connection a foot or so before connecting the sprinkler. Most sprinklers are 1/2" connections that are used for residential work.

    I just did some extensive rework on my irrigation system installed in 2007. All pipes are 1" since 1" irrigation valve are used most of the time and provide less restriction than a 3/4" valve. My community has reclaimed water (3/4" water meter) and I have too much pressure. I just got some MP rotor popups with a built in pressure reducer valve designed at 45 PSI. On one zone I had nine popups, installed a patio and now I'm just down to four.

    Here is a website with about the best information put together for irrigation systems. They cover it all.
    https://school.sprinklerwarehouse.com/design-and-install/
     
  17. Reach4

    Reach4 Well-Known Member

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    I think that measuring the pressures (and therefore differences/drops) during flow are key to understanding and curing the problem.

    Can the pump and well keep up? If yes, where does the pressure drop occur?
     
  18. h22lude

    h22lude Member

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    They are roughly the same height

    Just checked both again. With no water running, both spigots were showing roughly 50PSI and the pressure tank was just under 50PSI. I'll call that even.


    No I have a 40/60. I think the 80 reading was off. I just checked again and both spigots and pressure tank read roughly 50 (give or take a few pounds).
     
  19. h22lude

    h22lude Member

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    I just tested them all again.

    Pressure tank and both spigots read about 50PSI with no water running (obviously this will change as the system uses water but I tried to measure it all quickly to get roughly the same pressure from the tank).

    With 1 sprinkler on, the pressure tank was reading 45PSI and the other spigot was reading 45PSI. At the sprinkler the pressure was reading 35PSI.

    With 2 sprinklers on, the pressure tank and front spigot were both reading 45PSI again but the pressure at the furthest sprinkler dropped to 25PSI.

    I didn't test three sprinklers this morning but I have before and I don't get enough distance at each head. Having three sprinklers is basically useless.

    This is what I'm not understanding. Does this mean my pump can't handle the pressure? I do have the well completion report from my town when the well was drilled in 2012. The well is 800' deep, the static water level is 42' and the pump is at 485'. The recovery rate is very low which is why I assume they put the pump down that low. Could that be causing the pressure issue when a lot of water is being used? The pump has to overcome the depth before actually being able to get pressure to the house.

    I recently had a new pressure tank put in with the two big blue filters and soda ash. They used 1" PEX from the pressure tank to the big blue filters. Post filters they used 3/4". I had them put a tee before the filters with a valve so I could install the spigots before the filters. That is also 1" PEX so I could increase my spigot tubing all to 1". I was also thinking that could be used for inground sprinklers but I'm not sure I'll be able to do that if I have pressure issues.

    Edit: I just put a sprinkler at both spigots and ran them both. Pressure tank was reading 50PSI now. The back sprinkler pressure was reading just about 40PSI. So I'm seeing the same pressure lose (10PSI) when two sprinklers are running at different spigots as I do with two sprinklers running at 1 spigot.
     
    Last edited: Sep 8, 2020
  20. h22lude

    h22lude Member

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    I posted about a CSV months ago when I was looking at getting a new pressure tank. Valveman said a CSV may not work as well for my system. I'll have to look back to those posts. If the issue is with my pump, I don't think a CSV will help as the pressure going to the CSV wouldn't be enough to keep it at 50PSI.
     
  21. Reach4

    Reach4 Well-Known Member

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    1. any well or pump limitations will show up at the pressure gauge at the pressure tank. When you say that gauge showed 45 psi, did the pressure stay a that amount, or did the pump still cycle on and off? If it stayed the same during irrigation, that showed a balance that is good. You would not want to use more than that many gpm.

    So pressure drops after the pressure gauge cannot be blamed on the well or pump.

    The pump's real work is pumping water from the surface of the water rather than the level of the pump. So as the water level in the well drops, the pump will need more work for each gallon.

    If you are in danger of pumping the well dry, there are devices that can sense running out of water, and will shut down the pump for a programmable duration.

    Did they put a number on your recovery rate?
     
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