New Project: Water Cannon

[?ukas H?u?t?ler]

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

[Smooky]

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

[?ukas H?u?t?ler]

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?

[Smooky]

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=/

[?ukas H?u?t?ler]

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

[nukeman]

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.

[BobL43]

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

Bring along an air pressurized tank with water in it. Oh yeah, they have small ones called water canons/super soakers
http://www.hasbro.com/nerf/en_US/sup...|e|11722310094