New poster here. Need some help sizing a pump. I am not a well guy but a mechanic . Not scared to tackle the job but lack the knowledge and experience with wells. Also trying to learn what I can from this board. Lots of good info here. May be kind of long so bear with me and take it easy on me. I have a 4 in well used for irrigation, 2 garden sections with drip irrigation and 8 sprinkler heads throughout the yard. I do not know the age of the well. It is 4 in pvc casing. Seems to pump a bit of very fine sand(almost like silt) but water is very clear. Last fall the pump went out. Had my well guy who lived next door replace the pump. The old pump was a Grunfos brand. Labeling was almost unreadable except it looked to be 1.5 hp and could not determine the gpm rating. I decided to cheap out with a 1 hp pump, 10 gpm. Knew within a couple weeks that that was not enough volume from what I had before. Used the same Grundfos brand as he said it would tolerate the sand better than the other brands. He was working on finding me a replacement pump head with more gpm, was going to do it for free for me. Short story at 54 years old he passed 3 weeks ago. So now I'm going at it alone. I pulled the new pump and checked my well as there are no records on it at all. It is 62 ft deep. Water level is at 22 ft deep and the pump is set at 48ft deep. So I have roughly 25 ft of water. I don't know what the gpm rating of this well is. I do know that the old pump would run 3 sprinkler heads and cycle on and off. Couldn't keep up with 4 going at once. These are just the regular Lowes type cheap replacement heads. The well never once acted as if it was overpumped, even with 4 heads going at once. The new 1hp pump will barely cycle off with 2 going, 3 is just too much. I know this is long but I feel the more info I can give the better you guys can answer. I have been looking to just replace the whole pump again and install a Grundfos 4 in. 1.5 hp rated at 16gpm. Does this sound like a good choice? Also wondering is there anyway to pump the silt from the bottom? It feels like it may be about 8-12 in. deep. Thanks.
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From that depth a 25 GPM, 1.5HP would pump over twice as much as you are getting now.
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It depends on how much the well can make. If you have a 25 GPM pump and the well only makes 24 GPM, you could pump the well dry. But if the well makes 25+ GPM you won't.
Is there a simple way to figure well supply rate? I have no specs on this well other than what I have measured myself. My well for the house is quite different even though it is 20 ft away. It is 110 ft deep and records show water level is at 70 ft and supplies 15gpm. Kind of odd I think for 2 wells that close to be so different.
You just have to test it. Run the pump wide open for a few hours, if it will do that, then measure how many GPM's you get with a bucket test. If the production falls off while testing wide open, use a ball valve to restrict the flow so the well doesn't go dry, then do the bucket test.
Finally got to test my well. Flow rate was at 14.5 gpm. That is all my pump would go I guess since it is a 10 gpm. If I do go with a 25 gpm and it is too much flow is there a way to restrict it or cut the flow back? . Thanks for the help.
Yeah 15 GPM is about max for a 10 GPM series pump. But at least you know it will make 15 GPM. You can still use a much larger pump and a Cycle Stop Valve will restrict it for you if/when needed. A CSV will restrict the pump to match the amount you are using, which is how it stops the cycling. So if you put in a 25 GPM pump and your well will only make say 18 GPM, just never open more than 18 GPM, and the CSV will turn the 25 GPM pump into an 18 GPM pump.
Now if the well really only makes 18 GPM, then you could also use a Cycle Sensor to protect the pump from dry run if you do happen to open more than 18 GPM.
Now if the well really only makes 18 GPM, then you could also use a Cycle Sensor to protect the pump from dry run if you do happen to open more than 18 GPM.
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In the Trades
You stated that with 2 sprinklers going the pump barely shuts off and with three it never shuts off. This is not a bad thing. As long as the pump can maintain decent pressure continuously running is ideal. I realize you had more zones running before but since you already have the pump and equipment in the well why not just use what’s already there.
I realize cycling on and off is hard on a pump, just like an ac compressor but frankly it's just using more electric to run. The old pump had longer off cycles and a fairly quick recovery to the 62psi cutoff while delivering more volume. I guess I'm just hung up on the most pump with the best efficiency. That said I can water more at once and have it done sooner rather than taking all day to do so. All of my garden is on timers but all my sprinkler heads are manual shutoff valves
It is always more efficient to "water more at once and have it done sooner", even with a CSV. But the CSV will keep the pump from being destroyed when you are not using enough water to keep the pump from cycling. Pumps are not like compressors. The higher the pressure the harder a compressor works and the higher the amperage. With a pump the higher the pressure the lower the amps, so the pump is doing less and working easier.
Most people just do not realize how many times a day their pump cycles, or how bad it is for the pump. When I pin people down who say they don't think they have a cycling problem, they will say the pump only cycles maybe every 5 minutes. Then I remind them that there are 1440 minutes in a day, and a cycle every 5 minutes is 288 cycles every day.
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