Question
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Followup To
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Followup To
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My lawn irrigation system gets its water from a well. The well is 310' deep. The pump is located 163' down. The pump works only when the irrigation system is on. The water goes directly from the pump to the irrigation system--there is no tank.

When I started up this spring the pressure for the water was about 8 to 10 psi higher than it is now (went from 50 psi to 40 psi for a typical watering zone). I am interested in knowing what could cause the pressure to go down that much. Could the water table have gone down enough to cause it? Could the pump be suffering from old age (it's 14 years old)? I suppose there could be a leak somewhere but I don't see any water pouring out (of course the leak could be inside the well in the pipe that brings the water up). It would need to be a leak that would affect all zones.

Thanks for your input.";

Answer -
Ted,
Here are my thoughts regarding the drop in pressure. The pipe  that draws the water up is not the problem. If that was leaking the pump would lose prime and it would not pump any water at all. The water table level is not the problem -the same thing would happen. The pump is rather old and in the pump there is something called an impeller that will wear out  and cause it not to be efficient any more. I am assuming that you have not modified the irrigation sytem since you started it up in spring. If you added heads or changed nozzles to larger sizes, then that could be the cause of a drop in the operating pressure, because you are asking the pump to pump more water. I do not know if your irrigation system is zoned, where you have a timer that turns valves on and off the different groupings of heads or if it all just comes on at one time. I kind of need the answer to that question. Then I can maybe have you look for a leak on the system or at least determine if that is the problem.
         Let me know,
         Thanks, Jim


Follow up:
1.  Yes I have a zoned system.
2.  The pressure drop is on all zones.  I have a pressure guage on the main line and watch the readings as the system goes from zone to zone.  I have recorded the readings and note an across-the-board drop since the season began six weeks ago.
3.  Perhaps I misunderstood, but my pump does not pull the water.  The pump is located 163' down in the well shaft and it pushes the water up through an 1.25" pipe.  If there were a leak in that pipe the water would just return to the well and I would never know it is leaking.  In any event, I don't think this can be a priming problem.

Even with the reduced pressure I have sufficient pressure to service the system.  My concern is that this may be a warning of problems to come and that led to my question.

Many thanks for a careful analysis.
Answer -
Ted,
I guess I didn't read the question correctly. My fault. I think you are correct and that it does indicate something is going on. It may be the old pump. I don't know if you have any shut off valve on the piping or where you have the gauge in relation to the valves, bit if you could take a pressure test and watch the gauge and see if it drops under static pressure that would tell you whether you need to worry about the pump or the piping. You need to pressurize the pipe, then close the shut off valve, and watch the gauge and see if it drops quickly. A very slow drop will not cause a 10 PSI presure drop when running. Also the shut off valve needs to be tight and shut off the water completely. If it's an old gate valve it may not do that.

         let me know
         Jim

Jim

You certainly are putting alot of time and thought into this.

The pump is at the far end of a vertical 163' pipe that goes down the well.  That pipe goes through a pitless adapter and is connected to a horizonal pipe about 55' long.  The guage end of that pipe.  The pipe then continues out to the field valves which control the flow of water to the various zones.

There is a shut off (ball valve) about half way along the horizontal pipe.  There is also one just beyond the guage.  That's it.  To do the test you suggest I would need a shut off at the bottom of the vertical well pipe so in order to isolate it while under pressure.  Not having that I won't be able to do the test.

I'm afraid if the pressure down trend continues I will need to pull the pump and check the pipe.  If I go that far it may be economically reasonable to replace the pump (and maybe the pipe too).  After all, how many years can I hope to get from it, especially given that I have hard water (about 15 or so)?

Note:  The pressure drop occurred over the six weeks from initial spring start up until about a month later.  It could be the pump.  Or it could be a developing hole in the vertical pipe.  In either case, time will make it worse and treatment requires pulling the pipe and pump in both cases.

Thanks again.

TED  

Answer
Ted,
You're right about a presure test and your gauge set up and 15 years is a very good life span for the pump. You probably don't own any thing else that old that is still working. So, I guess just continue to keep an eye on that gauge and also keep an eye out for a main line leak on the system.
         jim