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Double acting hydraulic water pump

  1. Jun 14, 2009 #1
    I want to build a pump system using the water pressure from a 36 inch deep pond (up to 96" weather permitting) to pump water to a holding tank 100 feet above the 36" water level. after reading thru 15 pages of posts "water pumps" etc. on PF my head is spinning.
    At the dam there is access to a 6" drain supply 3 ft. below the water level. If I use a 100 ft. length of .750" plastic water line, i calculate i will need 19.13 psi (+ friction loss= ?). A 6" pvc pipe used as the cylinder is 5.50" ID. ,with a bobin piston and the addition of two 2" supply check valves and two .750" outlet check valves (one each at each end) I calculate around 30.64 psi.out of the homemade pump. If this is correct I will probably go to an 8" dia. pipe to cover any of my guess work.
    Is this plausable or am iI dreaming? Any comments would be much appreciated.
  2. jcsd
  3. Jun 14, 2009 #2


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    Staff: Mentor

    If I understand you correctly, you want to use (and discard) some water to drive a pump, pushing some water up 100'?

    Pumping water up to 100' requires 100*62.4/144=43 psi.
    A 36" deep pond has a pressure at the bottom of 3*62.4/144=1.3 psi.

    So to break even, not including friction and other losses, you'll need 43/1.3= 33 times as much water powering the pump as you can lift to 100'. Is that an acceptable ratio?

    I don't understand how you are trying to construct this, though. You'll need two pistons linked together, one 33 times bigger than the other.
  4. Jun 14, 2009 #3
    Picture three tennis balls in a sleeve, take two out, put the cap back on, add a 1/2 " and an 1/8 " hose on each end ,as water is pushed in the 1/2 " line the ball pushes to the opp end and expells the water out the 1/8 " line at that end, the 1/2 " line has a check valve on it(all four lines have check valves)

    the pump is constructed of pvc pipe, 5.5" id with a piston inside floating, each end cap will have a 2" supply with a check valve and a out going line with a check valve. the supply check valves are connected together and go to the 6" supply from under the pond. the outgoing check valves are tied together and feed the 100 ft. pvc pipe. other than trying to time the flow to get the piston to move one way or the other i figured the 5.5" piston with 1.3 psi of water pushing it to one end thus pushing the stored water out the .750 check valve and up the 100 ft .750 water line.

    please review this :http://tidalwaterpump.blogspot.com/

    if you would combine this system into one cylinder with one very large piston with the water supplied via a two inch water line at 1.3 psi. hope that is a little clearer.
    Last edited: Jun 14, 2009
  5. Jun 14, 2009 #4
    If you are interested in ram water pumps (water pumping water), google "ram water pumps". You will need running water to operate it. I used one for a summer. It had a 50 foot head, and pumped water over a 100 foot hill. I had to pull sticks out of it daily.
  6. Jun 14, 2009 #5
    Thanks, i'll do that now
  7. Jun 15, 2009 #6


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    Staff: Mentor

    Unless I'm missing something, you only have one piston in your setup and you are trying to manipulate pressure with the size of the connections. You can't do that. Pressure is a point property and is constant throughout a system at a constant elevation.

    It would help, though, if you could construct a diagram and/or actually show some of the math you used to get the numbers you have. Ie, by what calculation can 1.3 psi on one side of a piston create a pressure of 43 psi on the other? (or explain your numbers from the first post.... how did you calculate that 19.13 psi?)

    Notice in the link you posted, that there are two pistons, linked together, just as I described in my first post. Pressure times area on one piston gives a force on the linkage, which gives pressure times area on the other. Ie, for your setup, the big piston would need to be 33x bigger than the small one. But as in the link to a pump in a river, most of the water is discarded after it's gravitational potential energy (kinetic, in the case of the river pump) is used, not pumped away.
  8. Jun 15, 2009 #7
    hi, 3/4 " pvc water line: .750 id.
    h x pie x rxr

    1200 (3.1416 x .375 x .375)=530.14 cu inches
    530.14 / 234 =2.26555 gal
    x 8.4 = 19.03 psi

    the 5.5" piston has 23.758 sq. in.
    x 1.3psi =30.88 pounds

    sorry about the numbers , i've been looking at too many hydraulic sites.

    basically its like a hydraulic bottle jack, but with a 100 ft column of water .750 in dia. on top of the ram instead of a car axle.

    ok, i think i get it.... with a pressure of 1.3 psi pushing on the one side of the piston, the other side can only push 1.3 psi but can push a connecting rod with approx 30 pounds of force. i was thinking the weight of the collumn of water was the connecting rod.
    sorry for all the go round, i usually build it then troubleshoot later and figure it out with trial and error. thankyou
    Last edited: Jun 15, 2009
  9. Jun 15, 2009 #8


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    Staff: Mentor

    Ok, there, you just calculated the weight of the column of water, not the pressure at the bottom. Pressure is per square inch and you don't have a square inch at the bottom, you have 3.14*.375*.375= .44 sq inches. To get pressure, you have to divide that weight by the area: 19.03 lb/ .44 sq inches = 43 psi.
    Yes.... 30.8 pounds of force pushing on it. But on the other side, it has 23.758*43 = 1024 pounds opposing it!
    You got it now....

    If you can accept the loss of some of the water, you might still try this, though...
  10. Jun 16, 2009 #9
    thank you, got to go to work
  11. Aug 29, 2009 #10
    Hi. I just happen to be considering these types of pump (ram pumps and, for lack of a better name, double-piston pumps) for my water system. I'm trying to decide which is best for my particular situation.
    So far, I have found a great deal of information about the ram pump, but I have found very little hands-on information about the double-piston pump, although I have found one company selling what I think is the same pump (http://high-lifter.com/). I'm afraid that I have not yet discovered the common name for what I'm considering.

    Here are the characteristics of my site. The 2.5 gpm spring is about 35' above the house, giving me 15 psi, but I would like more pressure. The hillside above the spring goes up another 300' vertically (along about 500' of distance), which would give me more than enough pressure. I would like to use a pump that does not require any energy other than that of the falling water to pump my water up the hill to give me between 50 and 70 psi.

    I think a ram pump could do this, barely, but I am not confident it will be self-starting in the event that the flow rate goes down. I'm sure that a double-piston pump could be constructed to do this, but it is mechanically more complex than a ram pump. Finally, I live in Vermont, so the pump must be able to tolerate freezing weather or I will need to freeze protect it, probably by burying it in a tiny pump house below the frost line.

    Please comment on selection considerations of these two types of pump or any other pump that does not require external energy. Please also direct me to sites that describe the double-piston pump or compares it to other types of pumps. I have a solid understanding of the physics behind the double-piston pump, but I would like to see how others have solved the design issues involved in building one.
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