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Thread: Pump Life

  1. #1

    Default Pump Life

    I was reading another question here about Tank size and the bigger tank = fewer-longer cycles and a longer pump life.

    I have a 3/4 hp F&W sub with a 62 gal and a 20 gal Well X Trol tanks. It is set at 40/60. I was wondering if I would get more life out of it if I set my pressure at 40-70 or 30-60 or would I really not get that much more run time with either setting compared to 40-60? This furnishes water for 2 houses and about 40 cows. The pump is 13 years old and only had 1 problem and that was a split in the pipe right above the pump about 2 years ago. I hope it last 20 yrs or longer!

    Thanks for any input you might have.

  2. #2
    DIY Senior Member VAWellDriller's Avatar
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    You are absolutely right, that the fewer pump cycles, the longer the pump life. You would get a little more drawdown time by setting the pressure down some and adjusting the tanks, but I wouldn't change a thing. It sounds like the system is working well, and as long as the bladders don't fail, your pump should be fine for a long time to come. I've seen plenty of pumps last 20 years or more....hopefully yours will too. You should check the system periodically to make sure it is not short cycling, as that will cause pump failure.

  3. #3
    Moderator valveman's Avatar
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    I agree with VA. A 20 gallon size tank only holds 5 gallons of water. I am guessing you have a 10 GPM series pump. With a 10 GPM pump, I would have put in a tank that holds at least 10 gallons of water (44 gal size tank).

    You have already gotten twice the 7 year average life from that submersible pump, so you are doing something right, or your just lucky. Normally a 10 GPM pump would cycle itself to death quickly with only a 5 gallon tank. But it has a lot to do with how you use the water.

    Houses don’t normally use much water. About 300 gallons per day per house is common. So even if the pump cycles on/off for every 5 gallons used, it would only cycle 120 times per day to supply 600 gallons to the houses. That size pump has a maximum of 300 cycles per day, for which it should last about 7 years. So it doesn’t surprise me that it has lasted 13 years doing 120 cycles per day or less.

    It is the outside the house watering that usually cycles a pump to death prematurely. If you water the 40 cows with a full open garden hose (10 GPM), the pump should not cycle much, if at all. But if you have float valves on multiple watering tubs, that pump could cycle a lot. The same thing for irrigation demands, if you use 10 GPM the pump won’t cycle. But if you use one 3 GPM sprinkler for hours at a time, the pump/motor would quickly be damaged from the excessive cycling.

    Yes the fewer times the pump cycles the longer it will last. But increasing the size of the pressure tank is not always the best way to eliminate cycling. As you have seen, even with the small tank you have, pump cycling for just two houses is not that much of a problem. But if you ran a 3 GPM sprinkler 24/7, the pump would be cycling about 500 times per day, and it wouldn’t last long. Doubling the size of pressure tank would make it cycle 250 times per day, which is still not good.

    Even with a very small tank, if you used a Cycle Stop Valve the pump would run continuously 24/7 when using that 3 GPM sprinkler. Pumps are made for continuous duty. It is the cycling on and off that destroys them. Also with the small tank and a CSV, the pump would only cycle about 40 times per day for the houses, instead of 120 times per day as it is now.

    So if you want to stop the pump cycling, use a Cycle Stop Valve. A larger pressure tank would only reduce the number of cycles, which is good, but not as good as eliminating excessive cycling as when using a CSV.

  4. #4
    DIY Senior Member VAWellDriller's Avatar
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    Quote Originally Posted by valveman View Post
    I agree with VA. A 20 gallon size tank only holds 5 gallons of water. I am guessing you have a 10 GPM series pump. With a 10 GPM pump, I would have put in a tank that holds at least 10 gallons of water (44 gal size tank).

    You have already gotten twice the 7 year average life from that submersible pump, so you are doing something right, or your just lucky. Normally a 10 GPM pump would cycle itself to death quickly with only a 5 gallon tank. But it has a lot to do with how you use the water.

    Houses don’t normally use much water. About 300 gallons per day per house is common. So even if the pump cycles on/off for every 5 gallons used, it would only cycle 120 times per day to supply 600 gallons to the houses. That size pump has a maximum of 300 cycles per day, for which it should last about 7 years. So it doesn’t surprise me that it has lasted 13 years doing 120 cycles per day or less.

    It is the outside the house watering that usually cycles a pump to death prematurely. If you water the 40 cows with a full open garden hose (10 GPM), the pump should not cycle much, if at all. But if you have float valves on multiple watering tubs, that pump could cycle a lot. The same thing for irrigation demands, if you use 10 GPM the pump won’t cycle. But if you use one 3 GPM sprinkler for hours at a time, the pump/motor would quickly be damaged from the excessive cycling.

    Yes the fewer times the pump cycles the longer it will last. But increasing the size of the pressure tank is not always the best way to eliminate cycling. As you have seen, even with the small tank you have, pump cycling for just two houses is not that much of a problem. But if you ran a 3 GPM sprinkler 24/7, the pump would be cycling about 500 times per day, and it wouldn’t last long. Doubling the size of pressure tank would make it cycle 250 times per day, which is still not good.

    Even with a very small tank, if you used a Cycle Stop Valve the pump would run continuously 24/7 when using that 3 GPM sprinkler. Pumps are made for continuous duty. It is the cycling on and off that destroys them. Also with the small tank and a CSV, the pump would only cycle about 40 times per day for the houses, instead of 120 times per day as it is now.

    So if you want to stop the pump cycling, use a Cycle Stop Valve. A larger pressure tank would only reduce the number of cycles, which is good, but not as good as eliminating excessive cycling as when using a CSV.
    You missed the part about the 62 gal AND 20 gal tanks...that's why its working so well.....he's got about 20 gallons of drawdown...so using you're numbers of 300/house and 10 gpm pump, he's only cycling 30 times a day for the 2 houses.

  5. #5
    Moderator valveman's Avatar
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    Quote Originally Posted by VAWellDriller View Post
    You missed the part about the 62 gal AND 20 gal tanks...that's why its working so well.....he's got about 20 gallons of drawdown...so using you're numbers of 300/house and 10 gpm pump, he's only cycling 30 times a day for the 2 houses.
    Yes I did! Thanks VA! Life makes sense to me again. I couldn't see how he got 13 years life with only a 5 gallon draw.

  6. #6

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    I had a multi-stage jet pump before with a Sta Rite 20 gal tank. When I got this new F&W sub(10gpm) the well guy changed the tank too because it was about 20 yr. old. He put in the 20 gal Well X Trol tank and it worked fine but then I timed it and it took only 23 seconds for it to fill up. I decided I should add another tank so I bought the 62 gal Well X Trol and added it next to the other one. Glad to hear I have a pretty good set up. It will be 14 yrs old in March 14 and only had one problem with a split in the pipe at the bottom where it connects. I hope it does last a long time yet. I dont water any grass and the cow waterers are on automatic floats.

    Thanks for the info and comments. I will just leave it all as is.

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