3M recommends pressure tank size for their CBF100 carbon filter

Discussion in 'Water Softener Forum, problems, installation and r' started by hcw3, Oct 13, 2011.

  1. hcw3

    hcw3 Member

    Messages:
    30
    Location:
    western NY
    I have a new water system, including a new pump & pressure tank, chlorinator & carbon filter, and softener.

    The carbon filter is a 3M CBF100 "Backwash Filtration System".

    3M's documentation for the carbon filter specifies the following:

    "A PROPERLY SIZED PRESSURE TANK WILL REQUIRE A MINIMUM PUMP CYCLE OF 60 SECONDS TO REFILL FROM PUMP ON-TO-OFF PRESSURE"
    link: http://www.3mwater.com/media/catalog/product/pdfs/3MCBF_Manual.pdf

    Can anyone tell me what problems might occur if the pump-on to pump-off period is generally only 12 seconds (with all taps closed)?

    Thanks.

    --
    Harry
  2. Gary Slusser

    Gary Slusser That's all folks!

    That will burn up the pump motor very quickly and run up your electric bill.

    To solve the problem adjust the pressure switch too provide at least 20 psi between on and off.

    Check the well and pumps forum for instructions if you don't know how to do that.
  3. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,185
    Location:
    NW Ontario, Canada
    A pump motor builds up heat during the start current draw phase and should stay running for at least 60 seconds to cool off. Install a Cycle Stop Valve to stop the pump from short cycling and to give you higher constant pressure.
  4. hcw3

    hcw3 Member

    Messages:
    30
    Location:
    western NY
    Well, I apologize for not seeing your replies guys, thanks. I guess forum notification isn't working for me.

    I'm still struggling with the problem, and I hope I haven't damaged my pump by now.

    Gary, my pump is operating with a 20psi on/off differential. I believe the problem is that the pump and pressure tank were sized improperly. I'm thinking the installer simply screwed up.

    He's now installed a 5gpm 'flow reducer', that's got to go. It has an awful scream, which calls for hearing protection, when it comes on and for the 1st 20 seconds or so. After that the sound drops to tolerable, but still pretty noisy. Noise is one reason I installed a submersible!

    And still, the duty cycle is only 45 seconds or so. Argh.

    Is a flow reducer the right answer? Can it be installed in the well instead? It looks simple enough, about the size and shape of a 1" coupler.

    LLigetfa, I've looked into the cycle stop valve a little. From what info I could find, they seem like an excellent solution. Why are they so controversial in the plumbing world?

    Is a CSV going to be noisy like this nasty 'flow restrictor'?

    Thanks again for your help.
    Last edited: Mar 21, 2012
  5. Gary Slusser

    Gary Slusser That's all folks!

    Your pressure tank is too small. It's draw down is too few gallons for the pressure the pump is being operated at; I.E. 30/50 psi.

    Your driller or plumber that installed the 5 gpm flow control needs to remove it and refund all the money you paid for it. All it does is limit the volume of water you get out of the pump. He did that to make the pump stay off longer but you see it still isn't off for a minimum of 60 seconds (that is also required by all sub pump manufactures for regular less than 1.5hp pumps AND he should have seen that his 'fix' didn't fix anything after installing it and testing it.

    You probably have a 20 gal nominal captive air pressure tank, at 3/50 it will have a draw down of about 5.x galls. You need a larger tank that has a draw down of like 10 gals. Or you use a lot more power and eventually burn up the pump motor.
  6. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,185
    Location:
    NW Ontario, Canada
    The flow reducer is not the right answer. The CSV is a much more adaptive flow reducer that lets you use all available GPM.

    You would be best to ask CSV questions in the pumps and wells forum where valveman will see them. They do make a model that fits in the well if noise is a concern.

    Your current tank size would be OK if you used a CSV.
  7. hcw3

    hcw3 Member

    Messages:
    30
    Location:
    western NY
    Thanks much for your inputs. I'm interested in the CSV, but am cautious because I've seen disagreement about them.

    Gary, I can't tell from your comments. What size tank does your figuring suggest? The way I figured it, the tank would need to be 4 times larger, because the pump runs for 15 seconds now with the 20 gallon tank and needs to run for 60 seconds. Is an 80 gallon tank appropriate then?
  8. Gary Slusser

    Gary Slusser That's all folks!

    The draw down gals at the pressure you operate the pump dictates the size of tank and that all depends on the gpm rating of the pump and the static water level in the well. So you need to know the gpm and hp of the pump and what depth it is set at in the well, then find the pump chart for it and plug in those figures to find out what draw down gallons you need, then you find the tank that provide them at the psi you run the pump at.
  9. valveman

    valveman Moderator Staff Member

    Messages:
    4,583
    Location:
    Lubbock, Texas
    The CSV is a globe pattern, and only makes about as much noise as a ½ open faucet.
    Last edited: Mar 22, 2012
  10. hcw3

    hcw3 Member

    Messages:
    30
    Location:
    western NY
    Well, if that isn't a lot to chew on.

    What would a residential csv cost me, roughly?

    I've found that a new tank would cost me @ $ 450 not installed, as would a new pump, but the pump should be a bit easier - less pipe work to deal with.
  11. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,185
    Location:
    NW Ontario, Canada
  12. hcw3

    hcw3 Member

    Messages:
    30
    Location:
    western NY
    I've looked into the CSV, and the cost will be more than replacing either the pump or the tank.

    The cost of the CSV was quoted at $236, but then I would need to change my chlorinator pump which now simply turns on with the pump. Since the CSV would vary the flow rate, with the pump running all the while, I would need some kind of variable rate pump for the chlorinator. I spotted some in the $300-$400 range. Not sure how they work, but that's too much $$$.

    It looks like switching out the pump would be the best place to start (and then hoping the pressure tank is the right size).

    Is the well-driller's GPM rating the appropriate way to determine the correct pump size for my well?
  13. ditttohead

    ditttohead Water systems designer, R&D

    Messages:
    1,941
    Location:
    Ontario California
    Check out the Chemilizer HN55 pump, it uses the water flow to pump, and it has a set ratio. it is approximately $200 plus a chemical storage tank. The most common is 128-1 ratio. For every 128 gallons of water the house uses, it will pump 1 gallon from the chemical tank. Mixing a gallon of bleach with 35-45 gallons should get you into the 5-10 PPM range.
  14. hcw3

    hcw3 Member

    Messages:
    30
    Location:
    western NY
    Thanks Ditttohead. That one looks promising.

    How would I know what the ratio should be in my system? I can test the water coming out of the contact tank, which will tell me what ppm chlorine I have now in the tank, but the way the installer set it up was totally unscientific ("oh just mix a gallon with 3 or 4 gallons of water"). I called the guy who designed the system, and he said 'if you're getting 0ppm chlorine out your tap, then don't worry about it.'

    The water coming out of the well is high in iron and sulfur, though I couldn't tell you how high.

    Can I figure this out using the water test results that the designer used (if he still has them), or is it trial and error?

    Thanks.
  15. Gary Slusser

    Gary Slusser That's all folks!

    Finding the correct size tank to get the right draw down gallons is much easier than replacing a pump while hoping the too small tank will be OK for at least a minute off for the pump between starts.

    If the gpm the driller has is for the pump yes, but if the recovery rate gpm is for the well then no. That's the gpm of water refilling the well after using water. That has nothing to do with how many gpm the pump can deliver to the house. Call the driller and get the gpm and hp of the pump you have and ask him what size tank you need to get the pump to stay off for 60 seconds.
  16. ditttohead

    ditttohead Water systems designer, R&D

    Messages:
    1,941
    Location:
    Ontario California
    The basic calculation is simple on paper, but a little more difficult in the field. That is why I recommend the Chemilizer pump system, they are not affected by varying flows, pressures, etc.

    Clorox bleach (not generic) contains approximately 60000 ppm of chlorine. You need to reduce that to below 10 ppm. We use water to reduce that 60000 in the chemical storage tank. We then inject that dilution into the water stream in a controlled amount depending on the water condition. I am travelling for a few days so I do not have my charts in front of me, in general, if you keep the total chlorine level below 15 ppm, the carbon tank should have no problem. Of coure, you have to consider a few variables such as contact time, what type of storage, water quality, etc. to know the proper amount of chlorine to inject. Chlorine in a storage tank will also lose effectiveness over time, so mixing a huge batch that will last for several months would not be a good idea.

    I apologize if my calculations are off a bit, but these should be close. With a Chemilizer HN55 1-128 ratio pump, a dilution of 35 gallons water to 1 gallon of bleach should give you between 10-15 ppm chlorine after the pump/injection system. Other pumps, stenner, LMI, etc are usually adjustable in some way. The math is fairly simple if you can determine what the ratio of pumped/injected chemical to water used is.

    65000 / 35 / 128 = ppm chlorine

    Since I dont do these calculations daily, hopefully somebody on this forum who is familiar with proper chemical injection systems, (not the chlorine pellet systems) will add some better information for you.
  17. hcw3

    hcw3 Member

    Messages:
    30
    Location:
    western NY
    Well, tell me if my math is wrong, but from your figures (using 60000ppm for 6% Clorox):

    .06/35gal = .0017143...
    1:128 = .00001339...
    or 13.4 ppm

    So I figure the concentration/solution that my injector is doing right now is approx. 11ppm. Previously it was maybe twice that, before I reduced it, using a trial and error approach.

    Thanks ditttohead, for helping me to understand how to figure this!

    So 10 to 15ppm is the common concentration in most systems?

    How would I know if I could do less than that?

    Here's another whopper:

    When the system was first installed, no one thought to install the carbon into the tank. The installer blamed the supplier, and the supplier blamed the installer.

    It ran this way, at perhaps 24ppm, for two weeks (maybe at even 3 times that concentration for a few days).

    Any ideas what kind of damage was likely to have been caused to the rest of my system with the high chlorine concentration, esp. to the resin in the softener tank?

    If the resin fails, will it be obvious to me, perhaps in the shower?

    Thanks again!
  18. hcw3

    hcw3 Member

    Messages:
    30
    Location:
    western NY
    Gary, I should give you the whole picture about my system. (Sorry, it's kind of long...)

    Our well was probably drilled in the early 80s. The driller's long gone. The old pump was a Red Jacket that sat on top of the 20gal pressure tank. The pump was rated for @ 5GPM.

    We've updated with a new submersible and softening system.

    - the well is 47 feet deep
    - "10GPM" is marked under the well cap with a 6" casing
    - the water level in the casing is 5 to 8 feet from the surface of the ground
    - the pressure tank is @ 4 feet below ground level

    The plumber ordered an 8GPM 1/2hp submersible with a 20gal pressure tank. 8GPM was out of stock, so the plumber got the 12GPM 1/2hp - I questioned it at the time, though my knowledge is nil about these things.

    The new submersible hangs @ 10 feet from the bottom of the well - 25 to 30 feet below the surface of the water.

    We now have a brand-new 12 GPM pump (the cost of which I've deducted from my final payment to the plumber), and a new 20gal bladder pressure tank.

    If we were starting where the plumber should have, trying to figure out what pump to put in: the well recovery rate was rated at 10GPM by the driller, doesn't it make sense to put in a pump that pumps no more than 10GPM (or even 8GPM because of the well's age), and then size the pressure tank to match the pump's capacity?

    A couple of reasons I'd prefer starting by replacing the pump, rather than the tank:
    - The existing 12GPM pump will pump the well dry if it runs any amount of time, judging by the driller's capacity rating.
    - Isn't it easier to pull the pump and reinstall a new one, than it is to disconnect/reconnect all the plumbing that's necessary to remove and replace the tank?
    - doesn't the draw-down measurement depend on the pump being sized right?

    One other question. You're now mentioning a 60 second OFF time with the pump cycle. This conversation started with the question being about a minimum 60 second ON cycle. What amount of time should the OFF time be?

    Thanks for your patience here.
  19. ditttohead

    ditttohead Water systems designer, R&D

    Messages:
    1,941
    Location:
    Ontario California
    Thanks for doing the calculation with a calculator, I was doing it in my head in the middle of the night.

    The softener resin can handle a certain amount of resin, over time, the exposure is cumulative, so for arguments sake, lets say that standard resin can handle .5 PPM for 1 million gallons, Not knowing what type of resin you have, I am not sure of its total tolerance. A simple calculation and you can see that you may have used up a few months of the softener resins life in a week or two. Fortunately, resin is fairly inexpensive and easy to replace Assuming you get no more Chlorine into it, then it is only subjected to normal wear and tear which include sudden pressure changes, backwashing (physical damage), etc. All of these cause additional wear to the resin, but for the most part, they are almost nothing compared to oxidative damage. I would not worry about it considering how minimal the exposure was.
    Last edited: Mar 27, 2012
  20. hcw3

    hcw3 Member

    Messages:
    30
    Location:
    western NY
    ok, that's nice to hear.

    I really didn't want to make time to learn about changing the resin right now.

    Thanks.
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