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Thread: New Project: Water Cannon

  1. #1
    DIY Junior Member ?ukas H?u?t?ler's Avatar
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    Lightbulb New Project: Water Cannon

    Hi fellas,

    This may be an unusual question on this forum, but I thought I'd try posting it here. I hope I'm not violating your policies by doing so.

    I'm builing a water cannon for casual fun at the lake. I have a pipe with a diameter of 18 mm (≈4/5") that will serve as the "gun" which will project the water. The idea would be to use an electrical pump to suck water directly from the lake, which would be powered by a car battery or something similar.
    Now, I want this guy to be able to shoot a beam of a good 4 meters, or 12 feet.
    Let's say the hoses used from the water to the pump, then pump to gun, would be about 18 mm, what kind of power and output (gallons/h) will I be needing on the pump?

    I know nothing about this stuff, so layman's terms are appreciated. Also, if you have any tips to share on what is important to consider when doing this kind of project, I accept with open arms.

    Cheers,

    Lukas

  2. #2
    DIY Senior Member Smooky's Avatar
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    I have a 12 volt 5 gallons per minute flojet pump that I use on a 360 gallon portable tank. It will run one sprinkler head. I bought mine at a farm supply store.

    http://www.overtons.com/modperl/prod...hdown_Pump_Kit

    http://www.amazon.com/s/ref=bl_sr_sp...t&node=3375251

  3. #3
    DIY Junior Member ?ukas H?u?t?ler's Avatar
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    Quote Originally Posted by Smooky View Post
    I have a 12 volt 5 gallons per minute flojet pump that I use on a 360 gallon portable tank. It will run one sprinkler head. I bought mine at a farm supply store.

    http://www.overtons.com/modperl/prod...hdown_Pump_Kit

    http://www.amazon.com/s/ref=bl_sr_sp...t&node=3375251
    Awesome, thanks. You using this for a water cannon or a sprinkler? If the former, how far does it shoot with what beam diameter?

  4. #4
    DIY Senior Member Smooky's Avatar
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    I use the water tank and flo-jet pump to irrigate a garden. There is no power and no water at the location except what I bring in on a truck. I also use it to power a hose end sprayer for spot spraying. The tank gravity feeds the pump through a 50 mesh filter. I use the filter because the tank is corroding and I do not want to mess up the pump or clog up the sprayer etc. The pump is connected to a garden hose. It has about the same power as the hose at my home.

    http://www.northerntool.com/shop/too...ct_37142_37142

    http://www.amazon.com/SHURflo-255-31...ef=pd_sim_lg_3

    http://www.agrisupply.com/Flojet-Gar...28/&sid=&eid=/
    Last edited by Smooky; 06-04-2012 at 06:06 PM.

  5. #5
    DIY Junior Member ?ukas H?u?t?ler's Avatar
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    Quote Originally Posted by Smooky View Post
    I use the water tank and flo-jet pump to irrigate a garden. There is no power and no water at the location except what I bring in on a truck. I also use it to power a hose end sprayer for spot spraying. The tank gravity feeds the pump through a 50 mesh filter. I use the filter because the tank is corroding and I do not want to mess up the pump or clog up the sprayer etc. The pump is connected to a garden hose. It has about the same power as the hose at my home.

    http://www.northerntool.com/shop/too...ct_37142_37142

    http://www.amazon.com/SHURflo-255-31...ef=pd_sim_lg_3

    http://www.agrisupply.com/Flojet-Gar...28/&sid=&eid=/
    Awesome man, thanks. So I'm thinking of getting a 58 gpm pump. As far as I've understood, this baby would have a head of 28,5 feet, ≈ 14,25 PSI. How come smaller pumps that do like 26 gpm can produce 135 feet of head ≈ 67 PSI? Because the tubes have a smaller diameter?
    Which should I go by to estimate the power, i.e. the length and solidity of the water beam, the gpm or the PSI?

    Thanks,

    L
    Last edited by ?ukas H?u?t?ler; 06-05-2012 at 03:20 AM.

  6. #6
    Nuclear Engineer nukeman's Avatar
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    First we need to know under what conditions that you want to shoot 4m. I assume horizontal and held maybe 1m above ground.

    Acceleration due to gravity = 9.81 m/s^2

    distance (down) = 1/2 *a*t^2

    1m = 1/2 * 9.81* t^2

    Solve for t. t= 0.451s

    This means that the water needs to cover the 4m distance in less than 0.451s. If we neglect air resistance, that means the velocity coming out of the cannon needs to be at least (4m/0.451s) = 8.9 m/s

    Now, we need to find the volume of flow. Say the cannon is 18mm diameter. The area is: pi*18mm^2/4 = 254.5 mm^2 or 0.0002545 m^2

    Take area x velocity to get flow:

    0.0002545 m^2 * 8.9 m/s = 0.00226 m^3/s

    There are about 264.2 gallons per m^3, so the flow needs to be about 0.598 gal/s or ~36 gpm

    Remember, this doesn't include air resistance and would just barely get to 4m distance shooting horizontal from a 1m height even without air resistance. So, you should go for a pump that is at least 40-50 gpm.

    Next, you need the head. The head will be mostly due to the resistance of the line/cannon. I assume that the pump will be in the lake and that where you will use this will also be around the lake. If it is going to be used above the water source, that will need to be included as well.
    I imagine the pump with 28ft of head will be fine for this unless there is some aspect of the design that will cause a large resistance.


    The key is that the flow from the pump changes with head. If you have the pump curve for the pump, that is best. Otherwise, you may be looking at max gpm (which would be with no head) or max head (which may have almost no flow). What you want is a pump that will do 40-50 gpm when working against the head of the cannon (resistance of the line, form loss resistance on cannon exit, etc.). Would need to know more about the design to calculate the head.

    The next part may be to calculate pumping power and figure out how long the car battery might last on a charge.

    Good luck.

  7. #7
    DIY Junior Member ?ukas H?u?t?ler's Avatar
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    DUDE.

    This is awesome, exactly the kind of help I need.

    I would use this at the lake (10 m cable) and at a maximum height of 1,5 m. Let's count on that.

    So, I've had my eyes on this submersible pump of ~ 61 gpm, specs here: http://www.al-ko.com/87_1717.htm?prod_id=prod_1717
    Here's one with ~ 83 gpm: http://www.al-ko.com/86_1705.htm?prod_id=prod_1705

    The head values represent the maximum.

    Some of their smaller pumps pump like 3.800 l/h and get a head of 135 feet. Would this be preferable to get the same results?

    If I should find the pressure too low, I could just increase it by putting on a tighter nozzle, right?

    How about including air resistance?

    Do you think something like this would work for the battery? http://www.amazon.co.uk/Alphaline-06...8931985&sr=8-1

    Lot of questions, I know. Thanks for your awesome help so far.

    Peace

  8. #8
    Nuclear Engineer nukeman's Avatar
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    If you look at say the first link, there is a User Guide. On pg.2 of that guide, there is a pump curve. Let's look at the TWIN 14000 COMBI. Although it can do a max of about 61 gpm (nearly 240 l/min), that is with a very low head (less than 0,5 m). This means it couldn't even lift the water to where you are holding the cannon (1-1,5 m) and maintain this flow (and doesn't even include resistance of the lines). At 1,5m, the flow drops to ~210 l/min. Then you need to add the resistance of everthing (which I don't know with out much more details), but with the additional resistance, that pump may do say 100-140 l/hr, which may or may not be enough to get 4m+ with the 18mm diameter nozzle. However, you could experiment and try difference nozzle diameters. A smaller one does add more head against the pump (which means it will put out less flow), but the smaller nozzle also means that you need fewer l/hr to get the velocity (and distance) needed. You will also notice from these pump curves that when you get near the max head, the flow drops to nearly nothing. For instance, in the pump we talk about here, at 9,5 m head, the flow is only about 20 l/hr. At 10 m of head, the flow would be 0.

    Except for cost and possibly battery consumption, a larger pump (in terms of power) can be better. If it shoots too far, you can add an adjustable valve to control the flow/resistance and get the distance you want.

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    DIY Junior Member ?ukas H?u?t?ler's Avatar
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    Allright, so by "larger", do you mean larger than the TWIN 14000 COMBI?

    Thanks for your awesome help.

  10. #10
    DIY Senior Member Smooky's Avatar
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    For a cannon, powered by a car battery, for casual fun at the lake to shoot a beam of water a good 12 feet, you are making this too complicated.
    Both those pumps in the link are 230V, 50 Hz. A car battery is not going to power them. Where are you planning to put this cannon?

  11. #11
    DIY Junior Member ?ukas H?u?t?ler's Avatar
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    Quote Originally Posted by Smooky View Post
    For a cannon, powered by a car battery, for casual fun at the lake to shoot a beam of water a good 12 feet, you are making this too complicated.
    Both those pumps in the link are 230V, 50 Hz. A car battery is not going to power them. Where are you planning to put this cannon?
    Okay, got any tips on what kind of battery would be up to it? Not sure what you mean by where I'll put it.

  12. #12
    Nuclear Engineer nukeman's Avatar
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    What he means is that those pumps are designed to run on mains (household) power of 230v, 50Hz (AC). A car battery is 12v, DC. What you need to do is find a 12v pump.

    What he means by where you will put it is will is be near the lake (away from 230v power), I believe.

    I believe the TWIN 14000 COMBI would do what you need, but you would need the correct power source, so I think you will need something else.

  13. #13
    In the Trades Tom Sawyer's Avatar
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    Anything with enough power to do what you want that runs on a 12V car battery ain't going to run for long before the battery dies. You need a gas powered trash pump. Harbor Freight has them, so does Northern tool
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    DIY Junior Member ?ukas H?u?t?ler's Avatar
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    Yeah I want to keep this project green, are there portable batteries that can give 230V?

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    In the Trades Tom Sawyer's Avatar
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    http://www.pumped101.com/

    All you ever need to know is there....and then some
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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