Flow problem

255' well, water at 45 ft.
Just put in a new pump and motor: 1hp Grundfos 10S10-15 and 1hp 3W 1P Franklin 230V motor. 44gal tank @38psi and CSV1Z. Switch 40-60. Set up was for a sprinker system mainly.
I needed it to push my three Rainbird 3gpm(approx? is that right for this type of head??) Maxipaw impact/rotor type heads, 3 heads/station, 6 stations. So my requirement would be roughly 9gpm? 6 Stations usually run for 20min ea., so 2hrs total watering time.

The first 20-30min it runs fine, 40-50psi and pushes the heads. (By the way the CSV1Z only really holds at 50psi when I'm at less than 5gpm. That's frustrating! I thought it would hold 50psi at 10gpm? Why doesn't it regulate it at max flow? I even have it cranked way down) After 45 minutes of constant watering the pump struggles to keep up and slowly drops just below 40psi. The pressure gauge then takes a quick nose dive and will suddenly drop down to 10-15psi and hold for a few minutes. Then it will surge and go back up to 40 psi for a 15 seconds and after a 10 or so seconds it will drop back to 10-15. If I close a valve and restrict the flow the pump will begin to catch up and return back to 40-50psi and not have irratic pressure issues at all while doing so.
But when I open the valve up again to wide open the same thing happens. I'm not getting any air so I don't think it is running dry. I can't believe that would happen if my water is at 45' and well is 255' deep?

1. Is my pump the right pump for the job? The well guy said it was, but he just stood there 10 min and said, "look it pushes your heads nicely at 50 psi ", but didn't see what they do after 45min.
2. Am I asking too much in running it for 2 hrs at 40-50psi? (Course, it won't do that even if I wanted it to right now)
3. Should I really be trying 10min/6 stations for a total of 1hr. and just do that twice a day if I want to water 2hrs?
4. Am I running out of water? Again, I can't believe that would happen if my water is at 45' and well is 255' deep?


Any clues would be greatly appreciated!

Sorry, thought this was important too: They put the pump 15' off of the bottom.

A 10S10-15 will only deliver 10 GPM at 50 PSI from 160' deep. Until you pull the water below 160', you are getting 10 GPM at 50 PSI. As soon as the water level is deeper than 160', your flow rate starts decreasing. When the water level is at 220', that pump will only give you about 7.5 GPM at 50 PSI, or 10 GPM at 30 PSI.

You can either shorten the run time for the sprinklers so you don't pull the well down so far, or run only 7 GPM so the pump can give you 50 PSI when the water level is 220'.

Is that the pump that should have been put in? Or is there one that would do a better job for the well I have?

It sounds like that pump is perfectly matched to the well. If it were any larger, you would pump the well off. If it were any smaller you wouldn't get the flow you have now. If you reset your irrigation to 7 GPM, it may not even pull the well down. If you shorten the irrigation run times, and give a little time between zones, the well will recuperate enough to keep using 10 GPM. Either way should be fine. You just can't run 10 GPM for 2 hours at a time, or you are using more water than the well can supply.

valveman, so my water level is dropping from 45' to 220' in 45min? So only about 20ft from where my pump is at? I didn't think I'd have that much draw down. Or am I misunderstanding you?

Thanks! I will try to put the smallest nossle in the heads and see if I can reduce the gpm. (Although I think I might have the red ones(supposedly 2.5gpm @55psi) in already.) So if I have the red ones in already I will shorten the run times.

Thanks again.