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Old 01-26-2010, 04:43 PM   #1
adronl
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Default Great minds think alike

It seems from reading a few people's idea they might be onto an Idea for a gun I built last summer but no worries. I called mine a hand cannon it is pretty much a SC that is small and compact. It has a dual stage pump for speed, power and the ability to recharge on the go. I also included a schrader valve to vary the maximum power of gun. It would seem I never put up any complete pictures well a weak link got broken in my move but it is an easy repair so I will go ahead and post a picture.
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Old 01-26-2010, 04:59 PM   #2
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Default Re: Great minds think alike

Sorry bout the second post picture is large
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Old 01-26-2010, 06:16 PM   #3
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Default Re: Great minds think alike

I think I've seen that pump before since you suggested it somewhere else.

As a design suggestion, I'd advise a different layout that allows for the nozzle and ball valve to go right after the pressure chamber. Having bends and lengthly pipe doesn't allow for the flow of water to be as direct. Of course, it's far too late to change, but that can be done in the future.

That said, this design offers a considerably ergonomical solution. I'd say the LPD (having seperated air tanks for more air) would work better because dropoff can become an issue here (thus limiting water volume), but perhaps it's more managable than it seems.
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Old 01-26-2010, 09:22 PM   #4
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Default Re: Great minds think alike

The flow doesn't matter highly due to the way the gun works the pressure is built up behind the firing valve there is no air in the line the top chamber is just for water storage and storing the pressure. The long barrel adds to the flow being more laminar the valve opening is very smooth. The force of the water coming out of the barrel is opposite of the action of the internal parts cutting down on kick this gun can easily fire at 150psi. Last this gun is not a technically a cph or an aph it is a piston gun and I call it a hand cannon it isn't much larger than a store bought supersoaker

Last edited by adronl : 01-26-2010 at 10:49 PM.
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Old 01-26-2010, 10:20 PM   #5
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Default Re: Great minds think alike

I still suspect you would have got better performance with the valve and nozzle on the front end of the pressure chamber. But it's hard to know how much better.
I think it's also been shown that long barrels don't improve lamination much. Nozzle design does a lot more, as do lamination devices.

The recoil cancellation is a good point though. Though I'm not sure how much of an effect you'll get. Perhaps if you you weighted the piston you might be able to create a powerful recoilless blaster, which would be cool technically, but may be less good marketing-wise since recoil creates a sense of power.

EDIT: Actually, you can't reduce the recoil to zero always, because the mass of water travelling backwards reduces with firing. Indeed, an over-weighted piston would create 'forward recoil' at the start of the shot - not a desirable characteristic.
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Old 01-26-2010, 10:47 PM   #6
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Default Re: Great minds think alike

Well it here is my only way to illustrate this if you had a high pressure pipe coming into your house from the city 3/4" and at the t where the city meter is there is a stubout a short straight pipe coming off the t. Since there is no air in the line for distortion if that stubout were to break the water shoots straight out with great force even clearing dirt and the meter out of it's way. Even with all the turbulent bends the straight pipe makes the stream more laminar and able to shoot straight even without a nozzle due to the lack of air in the water to distort it. That is why my firing nozzle is at the very end water under pressure is also stored into the barrel and it is directly connected with a relatively straight shot for more water to be quickly forced in behind it.

Last the recoil of the water forces the gun back the piston moves from the front of the gun to the rear so the recoil actually wouldn't cancel out you r right there woops my bad It will definitely let you know it is powerful.

Unrelated I really need to update my profile pic I looked much creepier this Halloween
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Old 02-08-2010, 10:41 AM   #7
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Default Re: Great minds think alike

Quote:
The flow doesn't matter highly due to the way the gun works the pressure is built up behind the firing valve there is no air in the line the top chamber is just for water storage and storing the pressure. The long barrel adds to the flow being more laminar the valve opening is very smooth. The force of the water coming out of the barrel is opposite of the action of the internal parts cutting down on kick this gun can easily fire at 150psi. Last this gun is not a technically a cph or an aph it is a piston gun and I call it a hand cannon it isn't much larger than a store bought supersoaker

None of that matters. Yes, a long pipe will make the flow laminar, but so will using straws. Compared to the bend, the long pipe is nothing though. You can improve the design a lot by removing the bends.

I suggest that you put the firing valve in line with the pressure chamber. It's the bends that do the most damage to the stream. The air isn't getting distorted; the stream itself is. What a bend has to do is re-orient all the water particles, forcing them all into a different direction. That isn't good for the stream, and a lot of energy gets lost. A bend creates a lot of turbulence and also removes force from the stream (the force is absorbed into the bend, pushing it). That's why we always recommend a straight line from the chamber to firing valve: Any bend horribly damages the stream and decreases the performance a lot.

Steps like these can improve the design a lot and improve performance from that.
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Old 02-08-2010, 10:57 AM   #8
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Default Re: Great minds think alike

Well I say put your money where your mouth is. I am not using a water bladder or baloon system and my gun is not weak or made for children. The tiny little bends may plague you but for me no problem and I still get the distance of a SC. So do you care to bet on that and maybe you should ask a plumber about a pressurized system getting a leak. Maybe you could take apart a Supersoaker and realize that most of the guns don't shoot directly off the pressure chamber and have an actual barrel to make the flow more laminar.

Really you must not understand the simplicity of this gun which is better for me. I dont really care if you think the barrel does nothing or that the bend will ruin the performance. You could not back that up with scientific proof, actual test results and not theoretical math or guesses. I know it works fine you may be able to give other bad info but I know just how many failures and mistakes you have made in the past the fact that some of you act like an authority on the matters is laughable. Seriously dont say anything if you are not sure what your saying is 100% true and verifiable by tests not guesses

EDIT P.S. I can be an A$? in the morning. I apologize a little I guess

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Old 02-08-2010, 11:49 AM   #9
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Default Re: Great minds think alike

That reminds me of the Minicannon design that I posted, but I had the 2 parts attached to th tee (other than the PC) switched. that should provide more linear flow
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Old 02-08-2010, 05:12 PM   #10
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Default Re: Great minds think alike

Quote:
Well I say put your money where your mouth is.
I plan to do that. And I apologize if I came off as condescending or arrogant in my previous post. I didn't mean to be; I just was stating a couple facts, and I was only trying to say that the design can be improve. Nothing else.

Quote:
The tiny little bends may plague you but for me no problem and I still get the distance of a SC.
These bends are tiny. 180 degree is a large bend. I design my guns to avoid this problem because I know how bad it can get. I'll address that below a bit.

Quote:
So do you care to bet on that and maybe you should ask a plumber about a pressurized system getting a leak. Maybe you could take apart a Supersoaker and realize that most of the guns don't shoot directly off the pressure chamber and have an actual barrel to make the flow more laminar.
Last time I checked, most off-the-shelf water guns perform poorly.

All stock air pressure guns need a bend to work. They just won't work without it. But nowadays, most off the shelf water guns do a pretty good job at laminating the stream. Most CPS guns had straws in the nozzle (which is much better than just a long pipe), and nowadays many off-the-shelf water guns have converging nozzles to speed up the stream right before it exits. And they use ball valves too.

Quote:
Really you must not understand the simplicity of this gun which is better for me. I dont really care if you think the barrel does nothing or that the bend will ruin the performance. You could not back that up with scientific proof, actual test results and not theoretical math or guesses. I know it works fine you may be able to give other bad info but I know just how many failures and mistakes you have made in the past the fact that some of you act like an authority on the matters is laughable. Seriously dont say anything if you are not sure what your saying is 100% true and verifiable by tests not guesses
Well, I'll go into the math of it.

adronl, I hope you don't think that I'm trying to be mean to you or anything. All I'm doing is explaining why having bends is a bad idea in performance water guns. You've made great guns in the past, and I'm sure you'll make many more. But I'm just explaining the science behind this, and why this is an important thing for water gun performance. I was just pointing out that since you always build performance water guns, you always get the best results. This water gun has a design flaw that makes it perform less than expected. All I was trying to do was point that out.

Moving on: The math I will do is pretty easy, though one equation will look kinda hard, but I avoid the hardness through an assumption.

Let's first list all my assumptions:
  • Steady state -- I'm assuming that there is no variation in time.
  • Constant velocity profile -- This is to simplify the calculations, mostly to simplify the integral.
  • I'm analyzing a section of pipe between the chamber and before the firing valve. This simplifies the diagrams and math. From this assumption, the pressure at the outlet won't be zero since the water hasn't left the gun yet.

Okay, I'll explore too cases for comparison: a straight pipe, and a 180 degree turn. I won't go into the case for a 90 degree bend because the math gets messy (it involves a lot of vectors), but the idea is similar to the 180 degree case.





Better explain my variables:
  • Q = Flow rate
  • rho = Water Density
  • d = Pipe diameter
  • V = Velocity
  • P = Pressure
  • F = Reaction Force from a surface
  • KL = Minor Loss Coefficient

Let's start off with conservation of mass:



Okay, so from conservation of mass, the velocity entering my control volume is the same when it leaves. That means no mass will build up inside the control volume.

Let's move onto conservation of momentum:



Okay, this is the trick I did. I assumed the velocity is constant over the area, so it simplified the equation a bit. The integral equation says that changes in the velocity over the control surface mean that there are forces changing them. A change in velocity would result into a force, in other words. Also, the velocities are equal, so the whole left side cancels to zero.

This equation has the reaction force in it. This is a force that the pipe transfers to the water. Why does the pipe transfer it? Because the pipe isn't moving; it's static. So to remain static, it has to transmit a force if the water is pushing against it. It's Newton's Third Law.

No something interesting happens. In the straight pipe case (Case 1), the water isn't pushing against the pipe; it's flowing against it. There is no surface for the water to push against. So the reaction force is zero! The equation simplifies:



This means that there is no pressure drop at all. That's what you expect, ideally, for a straight pipe.

But what about the 180 degree turn? Well, the water pushes against the pipe while it enters, so there is a reaction force. Let's simplify and solve for it.



So a bend means that there is a reaction force from the pipe to the water, so that the pipe doesn't more. That means that there is a pressure drop. A drop in pressure means a drop in performance, just as I said before. Bends hurt performance.

But I'll prove it a second way. I'll move onto conservation of energy using Bernoulli's equation.



Okay, this is much simpler. I assumed that there some pressure drop, from minor losses, as the water moves forward. These minor losses are considered minor in large-scale problems, but in small-scale they affect the design greatly.

Back to the equation: The equation simplifies to a pressure drop from minor losses. This pressure drop is changed by the minor loss coefficient. That means that the higher the minor loss coefficient, the more pressure is lost. Simple enough.

But look at that, velocity is in there too. And it's squared. That means when performance increases, more pressure is lost! Obviously, any performance water gun (like yours adronl) needs to have as low a KL as possible.

How do you lower the KL? Simple: Have linear flow. A straight pipe has a KL of 0; a 180 degree bend has a KL of between 0.2 to 1.5 (depending on the situation). And with the velocity tied in, that means that the better the gun performs, the worse it actually will if designed with anything that greatly increases the minor losses -- like bends. Bends hurt performance.

Edit:

I did some quick pressure drop calculations, it seems that, for high flow rates especially, the pressure drop is sizeable. From the picture, I assumed your gun was made off 1" PVC. I then took the worst case scenario (which is how you should design, always) of KL = 1.5, and used the equation from above. Here's the graph:



This is unacceptable. adronl, this is what I was talking about. Small changes in design, like having a bend, greatly change performance. This graphs says that at 500 oz/s (what SuperCannon 2 gets) the pressure drop is 93 psi. That's a lot. Most guns don't even use 93 psi.

Of course, this is the worst case scenario. The best case scenario of KL = 0.2 is a bit better: only a pressure drop of 12 psi. Still, a performance water gun needs all the pressure it can get, so little things like this add up. Removing these little things is an easy way to improve the design and to drastically improve your gun's performance.
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Old 02-08-2010, 05:40 PM   #11
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Default Re: Great minds think alike

Interesting gun. Should perform pretty damn well!

I think you're getting the wrong impression of what Drenchenator is telling you adronl. He's saying it could be improved further, not that it's bad. He's trying to help you.

To say what Drenchenator said in a different way, according to the technical manual Charlotte pipe has available on their website, a branch run through a 3/4 inch tee is equal to friction loss from about 5 feet of pipe. A 90 degree elbow is equal to friction loss from about 2.0 feet of pipe. About 7 feet of pipe is not insignificant.

The performance increase probably won't be more than 10% in water output, but it still exists. That's all.

Also, the long pipe leading to the nozzle probably doesn't make the fluid much more laminar. You need tubes the size of straws. The straws prevent movement of water in the radial direction. A wider pipe can have movement inside of the pipe in the radial direction, so it doesn't help. If anything, it reduces performance slightly due to friction.

With that being said, there are losses associated with the use of laminators (straws) and these might reduce performance rather than increase it. Always compare before and after.

My suggestion for a future gun would be to use a hose leading from the pump to the front. It'll keep the same basic layout and have slightly better performance.
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Old 02-09-2010, 12:04 AM   #12
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Default Re: Great minds think alike

I do appreciate it and thanks for the math . The origional Statement Drench made sounds pretty harsh on performance loss. Like Ben said It should work quite well just wont be quite as powerful or efficient as a straight shot cannon. I knew this going in but the ergonomics were the main concern and I was trying to match the general layout & size of a production supersoaker. This design can be improved like Ben and the Drenchenator said but this gun is meant to be safer than stuff I normally build and appeal to a market like the people that come to this site as well as an adult.

Generally people here say I could tone down the power. The barrel does help a bit but the length can hurt performance and horizontal fire is no problem for this gun either it is pretty much just a 3"SC with an ergo layout. The flow was a concern but trust me the flow wont be held back that much the gun is designed to dominate in a water war and be mobile, you could actually try and have a water war with the Drenchenator, Ben, and other top builders here and have a chance.

I never really expected the same performance of a straight up SC but this gun can operate at a higher pressure than my air compressor can generate. All the SC guns I have made so far depend on the pressure my air compressor produces about 100-110 so this gun will have a little advantage over the normal pressure I use of 40-50psi. I dont think it would be good for someone to run around with a hand held more powerful than many SC's also the pump is dual stage you can get 150 psi and not really over exert yourself

As Drenchenator said there will be some perfomance loss but there are variables to that a best and worst case scenario generally you want to base off the worst case for anything really. I do get offended but not because there is no truth to what Drench said. It is that others here may not understand or be discouraged by advice given, maybe never building there own or a proposed design as a result. I have seen advice here that dismisses peoples ideas because for instance their idea isn't anything that has been presented or produced with parts or engineering proved to work well already documented on this site. Sometimes things don't seem like they would or could work but they do. Also sometimes things produced perform better than the conservative math predicts but usually not better than the best case.

Sometimes things change how we think and calculate this gun is not necessarily one of those. The B52 bomber was such a case many aviation experts and engineers believed it could not and would not even fly. We know from history it more than flew it changed history and was very successful they still use them decades later. Many advances like the computer performance/size ratio, cellphones and many others were once believed impossible by many it was the few that believed it was not impossible and pursued that dream despite popular belief.

Last edited by adronl : 02-09-2010 at 02:03 AM.
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Old 02-09-2010, 08:26 AM   #13
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Default Re: Great minds think alike

Quote:
The origional Statement Drench made sounds pretty harsh on performance loss.
On re-reading that, I did sound harsh. And I apologize. I only wanted to say that you could improve the design, and I thought I was going off similar lines of thought from previous posts.

Anyway, do you have any more pictures or statistics for this gun?
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Old 02-09-2010, 10:11 AM   #14
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Default Re: Great minds think alike

Some (myself included) did go overboard on the "no bends" rule a few years back, but I don't think we were quite as restrictive as you imply adronl. No one stopped making the APH despite it's required branch run through a tee. Sometimes bends are unavoidable. I think the rule should be "avoid bends when possible for best performance but don't feel bad if this can't be done."

As for dismissing ideas, over the years there have been a lot of bad ideas, and as I recall, many of them have been attempted before. I think I've said "No, you won't like that" and people did it anyway a number of times, so it's not like they have to listen to my advice. As I say about pressurizing air around latex tubing, if you think it's a good idea, prove me wrong.

No one's dismissed an idea because it hasn't be tried yet. People have evaluated a design and determined it wouldn't do what the builder desired or have some other significant disadvantage.

Sorry for straying off topic, but I wanted to clear this up.

I'd be interested in more photos too. You don't see stuff like this as often as you should.
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Old 02-09-2010, 11:18 AM   #15
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Default Re: Great minds think alike

Wow, wow, wow, wow! That whole conversation was way-past my knowledge! (sorry for that off-topic rambling)

The Hand-Cannon is sick-awesome! Do you plan to sell these, adronl?

..Oh and ya, do you have any statistics yet?
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