Shallow well plenty of flow, but takes time to build pressure

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Waybe

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Last year I installed a sandpoint shallow well (galvanized pipe) that is 30 feet to the bottom and and the water level is 21 feet down (for my sprinkler system)
It uses a 2 HP red lion pump with a 2 inch brass check value.
The gpm last year and this year are the same: ~20 gallons per minute.
Last year it would take about a minute are so for the system to build pressure and send water the sprinkler heads.
This year it has been progressively getting worse. Took about 2 mins in spring and then 3 mins a few weeks ago.
This morning I started it up and noticed after a couple of mins it was sending water to the sprinkler heads but there wasn't enough flow to push them all up. After 10 mins there was no change. I noticed the pump not to be at full prime. I could feel the cold water passing through the check valve but there wasn't enough flow to full open the valve and get the pump to catch full prime. I open the water tap a couple of feet from the pump and closed the main valve that runs to my sprinkler system. I could see the pump was producing water then after a minute it caught full prime. I measure the flow and it was 20 gpm, the same as last year.
What puzzles me is why the pump couldn't catch full prime when sending water to the sprinkler system, but could when a cut the main and sent it through the tap a couple of feet from the pump?
When winterizing the system last year, I removed the check valve and reinstalled it this year. Could it be a air leak before the check valve that was cause by me during reinstallation this year? When the pump is running to the sprinklers I don't notice the sound of air in the pump or any cavitation.
The first zone the pump sends water to runs uphill probably an elevation of about 15 feet and a total distance of 60 feet. Could the pump be having problems over coming the friction loss causing it not to have the beef to pull that 2 inch check valve fully open to draw the full volume of water?
The pump is only a year old.
I was thinking about switching the first zone to a zone that is at the same elevation of the pump.
If I shut off the pump and restart it an hour are so later there are no issues. If I were loosing water down the pipe given the distance wouldn't lose prime after an hour?
 

Valveman

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It does sound like a suction leak in that the longer it stays off the more likely to lose prime. But it is always easier to prime when there is no restriction on the discharge like the 15' elevation. Since 24' is the max you can draw with a shallow well pump, your 21' to water is getting close to not working. If the water level gets any deeper you will have a problem, and might be the problem now.
 

Waybe

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It does sound like a suction leak in that the longer it stays off the more likely to lose prime. But it is always easier to prime when there is no restriction on the discharge like the 15' elevation. Since 24' is the max you can draw with a shallow well pump, your 21' to water is getting close to not working. If the water level gets any deeper you will have a problem, and might be the problem now.
I reinstalled the check valve and Teflon taped the hell out of the threads. I also changed the first zone to a zone that is the same elevation as the pump. After sitting overnight and starting the pump, it took about a minute for the pump to catch full prime and pressurize the system. This is what I was seeing last year. I am guessing this is typical behavior with shallow wells pumps when connected to irrigation systems because the irrigation lines do not stay fully pressurized after being off overnight. So the pump has to ramp up refill the lines with water until the pump has enough back pressure of water to fully pull that 2 inch check valve all the way open. Please correct me if my assumption is wrong.
 

Valveman

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If you don't have any leaks the check valve on the suction should have water on both sides and open immediately when the pump starts. If it takes time to prime, the water is not there. But the pump may have primed and started pumping and what you are seeing is the time it takes to fill the discharge lines and get water to the sprinklers.
 
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