CPS in Backpack (not in gun)

Guides and discussions about building water blasters and other water warfare devices such as water balloon launchers.
RV1458
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CPS in Backpack (not in gun)

Postby RV1458 » Tue Jun 20, 2017 11:41 am

I've been thinking about building a water gun and have learned a lot from searching around sscentral.org and now this site. I had an idea for a gun that I haven't seen anywhere else (that I know of). Did I miss something? Is my idea not practical? Here's my idea, I welcome your feedback:

The backpack guns/cannons I've seen mostly use a non-pressurized water storage backpack and the pressurization takes place in the gun. I may have seen a few that pressurize the backpack itself as a basic pressurized reservoir system. I haven't seen any that use a CPS in the backpack. My thought is to use rubber tubing to create a CPS system inside the backpack itself that is pressurized using a garden hose.

Since you want fairly small ID tubing (minimize "wasted" water) I was thinking of creating four separate rubber tubes connected via PVC pipe in a line. When pressurized, each tube would be about 18" long (the height of the packpack). The CPS would pressurize via water pressure from a garden hose as it filled. The water pressure for my hose is a little less than 60psi which would eliminate the need for pumping (I read that the SS CPS2000 had a water pressure of about 45psi and most guns are far less than that). My goal would be to get about a gallon of water in the CPS tubes which should give a good total shoot time with constant pressure for the duration of the shooting.

Has this already been done? What issues might I face?

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Re: CPS in Backpack (not in gun)

Postby SSCBen » Tue Jun 20, 2017 11:44 am

Welcome to the board.

It's been done a few times, though not particularly well in my view. See this really simple blaster: http://www.sscentral.org/homemade/leftovers.html

There aren't any major issues. The biggest I can think of is that I imagine using multiple latex tubes in parallel as you want to might present some problems. If the tubes are not all of roughly equal strength, then you might get some tubes inflating while others don't. I have never experimented with this so I don't know how much of an issue it is.

If you can make a good design then I'd be very interested in seeing it. Keep us informed.

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Re: CPS in Backpack (not in gun)

Postby Drenchenator » Tue Jun 20, 2017 12:17 pm

This is definitely an interesting project. To add to what Ben said, I think another potential issue is the ergonomics of the backpack. Assuming that each tube is fully filled, a 4-tube backpack that is 18" tall would carry around 4L of water. Add in the weight of the piping and other mechanical parts and you are easily talking about 15 to 20 pounds (potentially). Carrying this around probably isn't much of any issue, but carrying it around easily may be, especially if you want balance and maneuverability.

I wouldn't assume that the rope straps used on Ben's Leftovers gun are a good design choice (though they work with the "cheapness" of the design, which is not a bad thing). I'd recommend looking into high-quality straps and possibly clipping the straps together and adding a belt if the weight starts to become an issue.
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RV1458
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Re: CPS in Backpack (not in gun)

Postby RV1458 » Tue Jun 20, 2017 12:39 pm

I was planning to use a rigid frame from a hiking backpack with good shoulder straps and waist belt.

That is definitely more weight that I was thinking though. I was thinking (WAG) more in the 10-15 pound range, but I suspect your more experienced guess is better than mine. Fortunately I'm 6'3" and in good shape, but I will have to give serious consideration to weight and consider dropping from 4 tubes to 3.

Appreciate all the feedback so far!

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Re: CPS in Backpack (not in gun)

Postby marauder » Tue Jun 20, 2017 3:43 pm

The Super Charger Power Pack was a CPS blaster with elastic pressure chambers in the backpack. One thing I noticed when I had a Power Pack was that each PC emptied at a different rate. I can't remember if it effected performance though. It does with my XP Pool Pumper Blaster, but that's AP and not in a backpack.

In regard to how this effects your design, I think I'd opt for 3 tubes. It just seems that less PCs are better.
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RV1458
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Re: CPS in Backpack (not in gun)

Postby RV1458 » Mon Jun 26, 2017 8:55 am

marauder wrote:The Super Charger Power Pack was a CPS blaster with elastic pressure chambers in the backpack.


I did not know there was a pack based CPS Super Soaker. Good to know! I did a little research on this and decided to purchase one on ebay to play around with. It's used, so who knows what condition the seals are in, but hopefully nothing that can't be fixed. If I can get it working well, then I'll skip trying to build one. If it doesn't work well, I'll use it as a case study for building a better one. Hoping it works well or only needs minor repairs.

If anyone has any suggestions or links for doing repairs or building a QFD (it doesn't come with one), let me know.

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Re: CPS in Backpack (not in gun)

Postby Drenchenator » Mon Jun 26, 2017 10:12 am

It is possible to build a quick-fill device. http://www.sscentral.org/homemade/vhs.html has some instructions as to how. http://forums.sscentral.org/showthread.php?t=3884 has some (older) discussion. It's been a while since I've seen a quick-fill device, but I think that all you really need is an approximately 3/4" ID pipe and some connection to a pressurized water source (which you should use a ball valve to control). The input device attached to the water gun already contains all the mechanisms to make it work; all you need is the correct size pipe essentially.
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Re: CPS in Backpack (not in gun)

Postby marauder » Wed Jun 28, 2017 12:35 pm

Quick fill devices are a lot of fun and very useful for backyard play. I used to wish that every blaster had one. I had to remove mine from my 600s since I replaced the nozzles with nylon spacers. The extra performance was worth it.
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Re: CPS in Backpack (not in gun)

Postby Drenchenator » Wed Jun 28, 2017 2:50 pm

I've always wanted to include a QFD in my homemade designs but never really figured out where to put it, so I never did it. I remember that the nozzles of some CPS guns that have pull valves (Splashzooka especially) could be automatically used as a QFD on certain nozzle settings, which was what I think should be the gold standard for homemades (less moving parts). The chance to fill your chamber quickly and automatically is too good to ignore, I think.
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RV1458
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Re: CPS in Backpack (not in gun)

Postby RV1458 » Sun Jul 02, 2017 11:44 am

I made my QFD and will try to get a picture here. I was going to use the PVC valve like I've seen others use, but then I saw a hose adapter for $7 that was much easier to turn, especially one handed, and decided to use that. It replaced two parts I would have needed otherwise so the cost was basically the same and I like it a lot better.

The 3/4" 90 degree elbow works perfectly. The smaller end of the elbow tapers inside to the perfect diameter.

I was surprised at how much force you have to use to push down on the nozzle or the water pressure will push the gun out.

The simple QFD is also easy to use when refilling other guns, unlike the SS QFD which could not be used to refill reservoirs.

Complete parts (4) list:

Gilmour Single Flex Connect Shut-Off Hose Adapter - $7
http://www.homedepot.com/p/Gilmour-Sing ... htype=text

Charlotte Pipe 3/4 in. PVC Sch. 40 90-Degree Spigot x S Street Elbow - $1.38
http://www.homedepot.com/p/Charlotte-Pi ... htype=text

Charlotte Pipe 3/4 in. PVC Sch. 40 Female S x FPT Adapter - $0.69
http://www.homedepot.com/p/Charlotte-Pi ... htype=text

3/4 in. x 2 ft. PVC Sch. 40 Pipe - $1.72 - only used about 2" of this 24" pipe
http://www.homedepot.com/p/VPC-3-4-in-x ... /202300505

RV1458
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Re: CPS in Backpack (not in gun)

Postby RV1458 » Sun Jul 02, 2017 12:23 pm

Here's a picture of the completed assembly: https://www.dropbox.com/s/um53bzybh2hiv ... 0.jpg?dl=0

Connect it to a hose and it's very easy to use.


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