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Thread: Pressure tank size

  1. #1

    Pressure tank size

    I am forced to install a new pressure tank at my summer home as the present one is shot. Our cottage does not have constant power and everything is powered by gas generators. It is on a mountain top lake. Constant power is not an option. I have a submersible jet pump in my well that supplies the water to the pressure tank. The pump is powered by a 4500 watt generator. Hence......the pump is only running when this very loud generator is turned on and the tank won't refill when the pressure drops without it being on.

    The water system only feeds a shower and a kitchen and bathroom sink. Hot water is provided by a Bosch propane on demand water heater. Model 125K.

    Now that it is time for a new tank....how large a tank should I install so that the generator does not have to be running full time for someone to take an average length shower? Keeping in mind that these Bosch water heaters will not heat the water once the pressure level drops below a certain point. I don't know what that pressure is off the top of my head and I am not at the cottage.

    Any assistance or recommendation will be appreciated.

    Thank you.


  2. #2
    Pump guy speedbump's Avatar
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    I am not too sure one of the largest bladder tanks made will do what you want. I would look at filling a very large tank, (3-5 hundred gallons maybe) then using a very small 12 volt RV type pump with it's own pressure switch used for showers etc. This can be done with a 12 volt battery.

    bob...

  3. #3
    Thank you for your reply.

    This has been a dilemma for us for years. Can I ask what this system might look like? We would still like the pressure tank for other applications. Can you pump from the well to the pressure tank and then have the pressure tank feed a 3-5 hundred gallon PVC tank. Would it require some type of shutoff to the 3-5 hundred gallon tank somewhere in the line between it and the pressure tank to maintain pressure in the main pressure tank? Would the PVC tank then just be connected to the hot water line of the plumbing and the main line from the pressure tank just go to the cold water outlets, or how would you go about running this chain of systems.

    And next...where in the lines would you place the RV pump for the hot water. Would this be between the 3-5 hundred gallon tank and the hot water heater? And maybe lastly....would the 3-5 hundred gallon tank have to be elevated substantially or would the RV pump make this not necessary?

    Thanks again.

    PJ Smith

  4. #4
    Pump guy speedbump's Avatar
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    I'm not really the expert on this, but for the most part, the
    pressure system would stay the same, with the exception of hooking to the house plumbing. It would feed the plastic tank. It would be controlled by a float mechanism. Like the one in your toilet. Then the RV pump would supply the house. I don't know what the biggest RV pump will do in gallons per minute these days. But with a little conservation, it should work well.

    bob...

  5. #5
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    I have seen this same type of situation on a peninsula that juts out into Massachusetts Bay with no power. All of the summer cottages there utilize generators to power a well pump. They like you do not like the noise of the generators and in fact have a suggested time of day to run the generators. Most of the cottages utilize multiple diaphragm tanks to store water under pressure. To determine the amount of storage you need, calculate the gallons per minute flow rate from the fixtures and add up the amount you will need between generator starts. Then use a tank drawdown table and use multiple tanks if you have the room.
    quote:Originally posted by speedbump

    I'm not really the expert on this, but for the most part, the
    pressure system would stay the same, with the exception of hooking to the house plumbing. It would feed the plastic tank. It would be controlled by a float mechanism. Like the one in your toilet. Then the RV pump would supply the house. I don't know what the biggest RV pump will do in gallons per minute these days. But with a little conservation, it should work well.

    bob...

  6. #6
    Pump guy speedbump's Avatar
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    If y'all really want to know how this all works, Hydropur (David) is the expert in this field and several others.
    Look for him mostly in water filtration instead of here.

    bob...

    Frequently asked questions at a glance.

  7. #7
    Ok. I will do that. Thank you all for your postings.

    Pat

  8. #8
    Past Newbie
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    PJ,

    1) What you need is a gravity tank. With a 500 Gal tank you can supply 4 persons for two days.

    2) You pump directly from the sub to the gravity tank. No more diaphragm tanks. You will need a level switch at the water tank (rotation molded polyethylene, not PVC), ball switch or electrode.

    3) If you can put his tank on a hill or tower 25' above your the level of your shower head you can get 10 PSI. No tower then go with the 12VDC RV pump. An Aquatec delivery pump can put out 3.8gpm (good for one thing at a time). These pumps are very compact and have their own pressure switch.

    4) When you run the generator for the sub you can also charge the battery or charge it with a solar panel. You didn't mention the production flow of the sub so I can't say how long it will take to fill this tank. But it will reduce the need for the noisy generator considerably.

    Hope this helps,

    David

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