Recently went downstairs to find a floor full of water near my HW Heater, softener and well pressure tank. Checked all 3 units and found multiple pinholes in the side of the pressure tank. Time for replacing. Also possibly time to increase size. Want some answers/opinions before I do it. **Current tank is a Goulds V200 (65 gallon). According to their site the drawdown for my 40/60 switch is 17.4 gallons. **Current pump is 3/4 hp Jacuzzi that produces 18 gpm according to the installation tag on its disconnect box. Researching how to size a tank lead me to understand 18 gpm should be sized at 1.5 gallons of drawdown per 1 gpm. That's a drawdown of 27 gallons. Seems like I'm short cycling my pump with its current 17.4 drawdown.

Looking at sizing up to an 86 or 119 gallon tank. The 86 has a drawdown of 23.03 gallons and the 119 has a drawdown of 31.86 gallons according to the manufacturer specs. My pump seems to be right smack in the middle of these. Would it be fine to move all the way up to the 119 gallon almost doubling my drawdown capacity? The pump would run longer per cycle but cycle less often. Drawbacks? Pros and cons? Assumptions: Not concerned about tank cost at this time. There is proper space for the 119.

Thank you.

2 Answers 2


As large as you can fit and afford is sensible. Fewer cycles and longer run-times is best for pump life. You can also use multiple tanks, but if you have space and can afford the big one, go for it.

  • I just bought a new WX-251 62 gallons Amtrol pressure tank. I have a 45 gallons Amtrol pressure tank. I thought the same that a larger tank would make sense sine fewer cycles and longer run time would put less strain on the pump but then heard about the need to size pressure tank and was worries I didn't do that. So just wanted to confirm that I should be ok? Anything I should be concerned about since I just went with a larger pressure tank without thinking about sizing it. Jan 10 at 2:40

You need to change from the old time diaphragm tank to a bladder tank. The diaphragm tank really is not efficient (are they even sold any longer? ). The bladder tank draw down is close to its entire volume. A 30 gallon bladder tank will be more effective than your diaphragm tank because ~1/3 of the tank total volume is used where the bladder is close to its entire volume in the high 90% range. The one thing I noticed after replacing a few of the old time tanks is they were full of mud in the bottom 4-6” below the drain port was solid mud, bladder tanks fill and drain from the bottom so they do not accumulate silt / mud in the bottom of the tank. If you want a larger drawdowns or longer between pump cycles go larger. The difference I have noticed is the bladder tanks are wider than diaphragm and usually 1/2 as tall for the same drawdown.

  • The Goulds V200 I am replacing has the fill/drain at the bottom so I'm confused with your thought process Ed. Appreciate the response.
    – Uwtriguy
    Oct 31, 2020 at 18:33
  • There are 2 types of tanks diaphragm and bladder a bladder tank uses almost its entire volume diaphragm do not and an additional negative with the diaphragm tanks I have dealt with is the mud issue if you have a bottom drain great but a bladder tank is smaller and will allow a larger drawdown. Gallon for gallon.
    – Ed Beal
    Oct 31, 2020 at 19:09
  • Thank you for the clarification Ed. Recommended line to look at?
    – Uwtriguy
    Nov 1, 2020 at 1:25
  • Heck, even plain tanks (no diaphragm or bladder - fun with waterlogging) are still sold - as are jet pumps. Perpetuating the archaich seems to be a thing in well systems... Anyway, good call on the tank type.
    – Ecnerwal
    Nov 1, 2020 at 13:13

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