Well Tank Type / Size

Discussion in 'Pumps and Tanks Well Forum & Blog' started by devans175, Jun 21, 2011.

  1. devans175

    devans175 New Member

    Messages:
    66
    Location:
    Maryland
    I need to replace my well tank. The existing tank is a 32 gallon well x trol. I have very acidic water so I thought it would be best to replace it with a composite of fiberglass tank.

    What is the proper size tank? The existing 32 gallon one seems to do just fine, but would there be an advantage to going a little larger? My house is 2/2 baths and it's just me living there. It's unlikly that there will ever be more than 2 people. I was looking at a 30 gallon or 40 gallon Wellmate. Any thoughts?

    Note: I'm in the middle of installing an acid neutralizer and I noticed the tank and surrounding fittings are in rough shap.. starting to leak. I decided I should go ahead and replace the tank "while I'm at it"..
    Last edited: Jun 21, 2011
  2. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    3,833
    Location:
    NW Ontario, Canada
    A tank is not sized to the number of people or the number of bathrooms. It is sized to the GPM of the pump with the intent of reducing excess cycling. Rule of tumb is that a pump should run for more than a minute, so a 10 GPM pump should have a tank with 10 gallons of drawdown. Of course you could also limit cycling with a CycleStopValve.
  3. Drewmcg

    Drewmcg New Member

    Messages:
    17
    Location:
    Ann Arbor, MI
    I'm no expert, but doubt that fiberglass would be an advantage, given that quality metal tanks have linings to keep the water from ever touching metal. With most of these tanks, the water is in contact only with a butyl (if a quality tank) or vinyl bladder or diaphram. Of course, if you install an acid neutralizer upstream of the tank, then acid should not be an issue in any event.

    I just finished diagnosing a storage tank problem at my house (flotec sourced Sears captive air tank). I would steer you away from a flotec model toward a higher-quality tank. The Amtrols have a seven year warranty, and should last 1.5-2 times that (or more, in your low-use application). The other brand that I read a lot of good things about was Flexon (though they seem to be harder to find).

    From my research, the proper sizing of a tank depends mostly on the flow rate of the pump. To determine this, you need two pieces of data: (i) how many seconds the pump runs from the time it kicks in to the time it stops; and (ii) the number of gallons (incl. partial gallons) it pumps during that time. For me, it was easiest to get these data in two steps. I took a one-gallon pail to my laundry sink, let the water run (fast, then slow) until the pump kicked in (light flickers when this happens), quickly close the faucet, and then start filling up pails and dumping them until the pump kicks in again (flicker). I did this a couple of times and took an average. Then I put away the pail and got out a clock with a second hand, and slowly drained the system until the pump kicked in (flicker), and counted the seconds until the pump stopped (flicker; click). I did this a couple of times and took an average. Number of gals divided by number of seconds times 60 = GPM "flow rate" of your pump.

    Next, calculate tank size by multiplying the flow rate by between 1 and 2 (assuming you have a 1/2 or 3/4 hp pump, as most homes do). The principle is that the pump wants at least a minute to cool between cycles, for best service life. The longer, the better (1 minute is a minimum recommendation). For example, if you have a 10 gpm flow rate pump like mine, you want at least 10 gals "draw down". The draw down is the number of gallons the system/tank will put out until the pump has to kick in again.

    Draw down is determined by (i) the size of the tank, (ii) the cut in/cut out pressures set by the switch, and (iii) some more esoteric factors such as elevation, etc. I found a factor on the web that told me that with a typical 40/60 cut-in/cut-out pressure such as mine, the draw down will be approximately .26 X "total volume" of the tank (expressed in gallons). Total volume is the total physical volume of a tank (the water side and the air side of a bladder/membrane tank; IGNORE the "equivalent" figures published by some web sites, which just confuses things to no end). So, a 44 gal tank will have a drawdown of 44 X .26 = 11.44 gallons. The pump will run a bit more than one minute each time the switch calls for more pressure, and will get at least a minute rest between runs (assuming not more than 10 gpm draw at all the faucets at one time).

    Tank manufacturers also publish drawdown for their tanks. Amtrol's figures seem generous; perhaps they have designed their tanks to yield slightly more drawdown per total volume than other tanks. More drawdown is nothing but good for the pump and for your electrical bill -- it means the pump cycles less. The only disadvantages to a bigger tank are: extra up-front cost; slightly more space requirement; the extra weight for whoever has to carry it to the basement/garage/etc. Another advantage of a larger tank is that the fewer cycles (theoretically) will result over time in less flexing of the diaphram, so that the tank should last longer. I do not know of any empirical data to back this up, but it makes intuitive sense to me.

    There is a whole other debate (kind of exhausting, actually) about using CSVs (Cycle Stop Valves, a proprietary pressure regulator) and smaller (e.g., 4.4 gallon) captive air tanks, rather than the traditional layout described above. The moderator of this forum (valveman) is the inventor of this device and has a web site dedicated to it, and extremely knowledgeable. If you have a heat pump and/or do lots of irrigation, you might find this to be a better setup, and the time to make that decision would be before you replace the tank. For me (2 people; 1.5 bath; no irrigation or heat pump; renting) I preferred the lower electrical usage of the traditional set-up, and have asked the landlord to install a 40+ gallon Amtrol or Flexon tank. Good luck!

    p.s.: You probably want to nail down any modifications to your set-up before installing the new tank (e.g., acid neutralizer; chlorine-injection pump), so that those fittings can be plumbed in at the same time. Moreover, a union installed between the "T" and the tank would make future service/change of the tank much easier.
  4. valveman

    valveman Moderator Staff Member

    Messages:
    4,381
    Location:
    Lubbock, Texas
    Drewmcg, I applaud you for all the research. You have certainly done your homework, but I disagree with your conclusion. You should have noticed during you draw down and run time testing that the “flicker” is not a good thing. Even with no irrigation or heat pump, you would still benefit from a CSV and a smaller tank. With the CSV your pressure would stay constant while taking a shower instead of cycling on and off and “flickering” the lights several times while you are in the shower. Showers are much better and more enjoyable when the pressure stays at a constant 50 PSI with a CSV, instead of cycling on at 40 and off at 60 over and over again.

    The electric bill for a pump used strickly for a house is only about 5 bucks a month. The CSV should not increase the electric usage, but the worst case would be to add about 3 bucks a month to the electric bill. It would take many years to make up the difference in cost of a 44 gallon tank compared to a 4.4 gallon tank at 3 bucks a month. And that is not even considering the extra life the CSV will add to your pump, pressure switch, and everything else in the system that cycling normally destroys. Your landlord would be wise to do his own research and install a CSV to make his pump system last longer. As a renter you would like the constant pressure. But if you have never experienced constant pressure, you don’t know you are missing something.

    The debate is “exhausting” because there is nothing intuitive about a pump system. Everything is opposite of what you would think. Pump installers with many years of experience still do not understand, as they also think it should be intuitive, and its not. Pumps are not suppose to cycle on and off, they are made for “continuous duty”. Restricting a pump with a valve actually makes its work easier, not harder as you would think. And smaller tanks are now better than large tanks, so you don’t experience such long intervals of high and low pressures.

    A so called “properly sized tank” is what the pump, motor, and tank companies want you to do. That way they can predict a short life span for your pump system, and get to sell you about 3 or 4 pumps and tanks instead of one in 20 years. If I were doing a bucket test and trying to be intuitive, I would probably come to the same conclusion. However, decades of experience and replacing thousands of pump systems has taught me that eliminating cycling is the best thing for a pump system.
  5. devans175

    devans175 New Member

    Messages:
    66
    Location:
    Maryland
    I tested my flow rate according to instructions I got when I purchased my acid neutralizer. It's 4 GPM.

    The fittings are where I'm running into problems. The calcite/corosex neutralizer I settled on and purchased instructs you to install it after the tank, thus leaving the tank vulnerable. Even if the tank itself is impervious, the point that you connect to the tank may not be. I'd prefer to eliminate the metal fittings and connections on the untreated side of the system.

    I found a web site that performs the calculations. Here's the link:
    http://wellmate.com/en-US/support/calculator/

    Based on what I've read here and elsewhere, I think I'm going to go with the 40 gallon.
    Thanks!!
  6. valveman

    valveman Moderator Staff Member

    Messages:
    4,381
    Location:
    Lubbock, Texas
    No problem. Like I said, if you have never had constant pressure, you will never know how good it could have been anyway. BTW, a CSV will still work with a 40 gallon tank. But after you see how a CSV works, you will know the 40 gallon tank is excessive.
  7. Drewmcg

    Drewmcg New Member

    Messages:
    17
    Location:
    Ann Arbor, MI
    Not to quibble, but if the landlord pays $500 for a quality 44 gal tank (plus installation), rather than $250 for a CSV + quality 4.4 gal tank, then the delta is $250. (I acknowledge that these figures might be off a bit.) In S.E. Michigan, marginal electricity costs 12.5 cents/KwH. I've seen you use 7 cents and 10 cents/KwH for your dollar/month calculations, so do not know what figure you used for $3/mo. Assuming $5/month penalty with the CSV and a 15-year tank life, the extra $150 for the 44 gal tank setup would pay for itself in 50 months (50 X $5 = $250); or in 83 months at your $3/mo. figure (83X $3 = $250). If the tank lasts 15 years, the extra investment will pay for itself two or three times over in that time frame.

    Of course, this does not consider pump replacement costs. In a low, intermittent use context such as mine, I know of no empirical data on pump failure differentials. The difference in pump cycles in my application between the 44 gal tank and the CSV/4.4 gal tank setup would likely be minor (maybe only 3 cycles a day). That's a thousand cycles a year, which seems minimal in pump life expectancy terms.

    As far as the shower goes, I use a low-flow showerhead (under 2 GPM) to save energy; I do not expect the pump to cycle more than once per shower--which it would do with a CSV setup anyway. The flicker is seen on basement incadescent, not my shower CFCs. That leaves the pleasure of constant pressure v. average pressure with a 20 psi differential. Not a big deal to me, but others might disagree. (P.S. If I had a high/persistent water use situation, I'd be sold on a CSV.) Cheers!
    Last edited: Jun 21, 2011
  8. valveman

    valveman Moderator Staff Member

    Messages:
    4,381
    Location:
    Lubbock, Texas
    It has been my experience that the time it takes for a big tank to pay for itself in energy savings is about how long the tank last. So the big tank is not really saving anything. I have also tested systems with low flow shower heads and have found that they don't really save water. People with 2 GPM shower heads just take showers that are twice as long as people with 4 GPM shower heads. With low flow shower heads it takes twice as long to get the soap rinsed out of my hair. But I know people who use a hand wand and take a Navy type shower. Now that is conserving water. I want a shower with good pressure and feel cheated when I don't get it.
Similar Threads: Tank Type
Forum Title Date
Pumps and Tanks Well Forum & Blog Replace pneumatic tank with bladder type tank without removing bleeder valve? Jun 26, 2014
Pumps and Tanks Well Forum & Blog Best type of earthquake resistant connection from pitless to tank? Nov 10, 2013
Pumps and Tanks Well Forum & Blog hp vs. bladder type tank May 8, 2011
Pumps and Tanks Well Forum & Blog Air leak at valve stem in bladder-type pressure tank Oct 18, 2004
Pumps and Tanks Well Forum & Blog Question about WellMate pressure tank Yesterday at 5:47 AM

Share This Page