Unusual pressure tank question

phredo
phredo Registered Users Posts: 11
I decided to use a SimplePump to provide my household and garden water from my well. Although these are usually hand-powered, I am going to use the electric motor driven version as a stand-alone system, and it will give me about 7 gal/min from a 1/3 hp motor. The SimplePump is a type of pump often called a "windmill pump". It has a long rod linkage that goes down inside a water pipe to activate a piston that brings water up the pipe each time the handle is pumped. The electric motor at the top will take the place of hand pumping, but the effect is the same: water will come out in spurts, rather than a steady flow, each time the linkage goes up and down.

This varying output will have some effect on how a pressure tank will behave, I am sure, and the manufacturer agrees. He suggests that to keep the pressure switch from registering "false positives" or "false negatives" due to sudden, but temporary, increases and decreases in pressure, I should try to mount the pressure switch "downstream" of the pressure tank so that the pressure tank will act as a sort of buffer for the sudden pressure changes. He also suggested that I might want to install two pressure tanks, with the switch between them.

These suggestions sound reasonable, but I would like to get some further input from people who have some knowledge of how water behaves and/or have had some experience with such a problem. By the way, I installed the pump with the hand operated handle today with a friend's help. It took us about 35 minutes for the 45' deep installation, with me doing about 30 minutes of prep time first.

Comments

  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Unusual pressure tank question

    Just as a quick thought, I would install a small expansion tank between the pump and the rest of the plumbing. I would then install a check valve between that tank and the larger useable tank. That way the expansion tank takes the surge from the pump, and the check valve doesn't allow that pressure to bleed back through. I would then install the Pressure switch on the bigger tank. (An expansion tank is just a much smaller pressure tank)

    Sounds good to me,, but if I think of it some more and figure why it is a bad idea, I'll let you know.

    Tony
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Unusual pressure tank question
    icarus wrote: »
    Just as a quick thought, I would install a small expansion tank between the pump and the rest of the plumbing. I would then install a check valve between that tank and the larger useable tank. That way the expansion tank takes the surge from the pump, and the check valve doesn't allow that pressure to bleed back through. I would then install the Pressure switch on the bigger tank. (An expansion tank is just a much smaller pressure tank)

    Sounds good to me,, but if I think of it some more and figure why it is a bad idea, I'll let you know.

    Tony

    Absolutely 100% correct, Tony! :D

    EDIT: Forgot to mention; set the first tank's bladder pressure at least 2 psi lower than the main tank.
  • phredo
    phredo Registered Users Posts: 11
    Re: Unusual pressure tank question
    icarus wrote: »
    Just as a quick thought, I would install a small expansion tank between the pump and the rest of the plumbing. I would then install a check valve between that tank and the larger useable tank. That way the expansion tank takes the surge from the pump, and the check valve doesn't allow that pressure to bleed back through. I would then install the Pressure switch on the bigger tank. (An expansion tank is just a much smaller pressure tank)
    Tony

    Thanks so much. That's pretty similar to what the pump manufacturer said, except I don't think he mentioned placing a check valve after the first tank, and I couldn't quite get the concept. With a check valve it makes more sense to me. Do you think I would also need to install a check valve between the pump outlet and the expansion tank as a general sanitary precaution, or is that overkill? Also, do you have any sizing or brand ideas for the expansion tank? Small pressure tanks seem to be fairly expensive for what they are, and I thought I may be missing out on some of the types or sizes or models or brands.

    And thanks, Cariboocoot, for the 2 psi difference advice.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Unusual pressure tank question

    You don't need a check valve between the pump and the small tank. That tank needs to be at least 2X the volume produced by one stroke of the pump. Since these "Simple Pumps" are quite low in volume, a standard 5 gallon or even 3 gallon tank will probably provide enough 'shock absorbing' to even things out. You can take the pressure of the small tank's bladder down as low as 10 psi below the main tank if necessary.

    I actually have a similar set up on my house, which is connected to a badly designed 'community' water system. As the last house on the line (they didn't loop it as they should have) my water pressure is subject to wide variations depending on how many other taps are on and can 'bounce' up and down fairly quickly. The check valve and tank keeps the pressure consistent, as it only fills when the line pressure is higher than the tank pressure - no dropping house pressure bank into the main, as it were.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Unusual pressure tank question

    Contact your local wholesale pluming house, (Ferguson/Woolsey/Keller etc) or even you local Home Depot and look at a hot water heater expansion tank,, perhaps 2 gallons.

    Pretty common, fairly reasonable.

    Intuitively, I would still keep a check valve between tanks, and perhaps one at the pump. They're pretty cheap.
  • phredo
    phredo Registered Users Posts: 11
    Re: Unusual pressure tank question
    icarus wrote: »
    Contact your local wholesale pluming house, (Ferguson/Woolsey/Keller etc) or even you local Home Depot and look at a hot water heater expansion tank,, perhaps 2 gallons.

    Pretty common, fairly reasonable.

    Intuitively, I would still keep a check valve between tanks, and perhaps one at the pump. They're pretty cheap.

    Thank you. This is such a great forum! I have been thinking about all of this for 6 weeks and didn't know who to ask. :D