first homemade - technical questions

[Spindoctor]

Hi everybody!

I'm about to plan my first homemade water blaster. You can see the plan here.

Still, there are some technical questions unsolved.

1. I'd like to use a typical soft-drink-bottle as a water tank. This idea has at least two advantages: The bottles can be replaced quickly and cheap and I can use different sizes of water tanks. I want to cut a hole in the screwtop of a bottle and glue it on the place where the water tank is supposed to be.
   Now here's the question:
   As I pump water from the WT to the PT, I suppose a low pressure inside the water tank, that would deform the bottle. What can I do?
   My attempt was to apply a third check walve near the water tank (the one to the very right on my plan), but I think this solution is suboptimal.
2. As a pump, I thought of using a bike pump with a small adaption (so that it is not sucking air from the open side.
   Would it work?

Thanks for your help,

Spin

[Ben]

Welcome to Super Soaker Central!

As I pump water from the WT to the PT, I suppose a low pressure inside the water tank, that would deform the bottle. What can I do?

Yes, the negative pressure differential will cause the water reservoir to collapse. This problem can be fixed with a vent hole. Ideally the vent hole will have a check valve (as you know), but that's not necessary. Just put a small hole in the cap you would fill the reservoir with and don't turn the gun upside down.

As a pump, I thought of using a bike pump with a small adaption (so that it is not sucking air from the open side.
Would it work?

I have not seen a bike pump adapted for this, but I suppose it is possible. I don't see any reason why it couldn't be adapted, but I can see plenty of reasons why you wouldn't want to adapt a bike pump. Adapting a bike pump definitely is going to be harder than making a new pump. The pump also has too large of a diameter seal, making achieving a high pressure more difficult (though if low pressure is fine by you or you are very strong, this may be less of a problem).

My other suggestion would be to avoid a plastic bottle for a pressure chamber. A plastic bottle might seem like a good idea to save money, but I wouldn't suggest it unless you didn't have a choice. PVC is much stronger and much safer. I never have seen PVC break because of high pressures, but I have seen plastic bottles break because of high pressures. You'll also run into problems getting the bottle to attach permanently, though, that would be the least of my concerns given the fragility of the bottle.

Good luck with your project!

[Spindoctor]

First, thank you, Ben!

Yes, the negative pressure differential will cause the water reservoir to collapse. This problem can be fixed with a vent hole. Ideally the vent hole will have a check valve (as you know), but that's not necessary.

ok. If I would use a check valve (which would be better, because the bottle in my plan has only on hole - the one that bottles usually have ) could I apply it at the place it is applied in my plan or would I have to fear the consequence to pump air instead of water inside the PC?

I have not seen a bike pump adapted for this, but I suppose it is possible. I don't see any reason why it couldn't be adapted, but I can see plenty of reasons why you wouldn't want to adapt a bike pump. Adapting a bike pump definitely is going to be harder than making a new pump. The pump also has too large of a diameter seal, making achieving a high pressure more difficult (though if low pressure is fine by you or you are very strong, this may be less of a problem).

When I stripped down my bike pump, this adaption seemed really easy. Just two parts that are beside each other would have to be glued together.
But I didn't realise, that the large diameter would be a problem. Which diameter would you suggest?

My other suggestion would be to avoid a plastic bottle for a pressure chamber.

Yes I didn't want to use a plastic bottle as PC. Only the WT.

Thanks,

Spin

[Ben]

could I apply it at the place it is applied in my plan or would I have to fear the consequence to pump air instead of water inside the PC?

You could put the valve there. However, I'd imagine that it wouldn't be ideal because some water will leak out and it'd make some "slurping" noises. Valves that suck air into a water only environment don't sound too good usually. Super Soaker puts their valves in the cap. Any place on the top of the reservoir is a good place because it would be sucking air into an air environment.

But I didn't realise, that the large diameter would be a problem. Which diameter would you suggest?

Most Super Soakers use a 5/8 inch diameter pump tube. Most homemade water guns use a 5/8 inch diameter pump tube. 5/8 inch seems to be the "standard." If you are very strong I would suggest something larger such as 3/4 inch.

The problem with larger pump diameters is that they make achieving a higher pressure harder. However, smaller pumps also pump less water, taking more pumps to get the same amount of water. Some water guns such as the SS 300 use a large diameter, low pressure pump and still get great performance. To do this, you will need a very large PC capacity to prevent the pressure from building up too quickly. Sadly I haven't seen anyone take this approach.

[Spindoctor]

Thanks for all your help, Ben!

Now I come to the most important question - I guess it is also the one it is most likely that you can't help me.

I've visited some hardware stores near to my place, but couldn't find most of the parts that are needed.

I live in Austria (Europe). Has anybody got an idea, where to buy all this stuff?

Thank you...

[Ben]

Yep. This might be a little harder for me to help you with because I live in the United States. Here, even smaller hardware stores have an adequate enough supply of PVC to build a water gun.

I have been told that PVC can be very hard to obtain in parts of Europe. Typically this means that people won't make a water gun, which is bad. If you are dedicated, you can find PVC from larger warehouses. Check out a phone book for plumbing supply stores or warehouses. The PVC sadly will be very expensive from what I have been told if you choose this route.

Copper pipe apparently is more readily available in Europe than PVC is. This is good and bad. Copper pipe is likely more expensive than PVC is here. It also is heavier. You also have to weld the pieces together. However, copper pipe is also many times stronger and makes for a very impressive looking water gun.

If copper pipe isn't available locally, take a look at what is and post back here. Water guns can be constructed from most any type of pipe. PVC might be the most common way, but it surely is not the only way. I've considered making one from a bunch of threaded brass pipes because no welding or cementing is necessary. Anything is possible.

Please give this a good try because I have been interested in the availability of water gun parts in Europe for quite some time. I would like to help people make water guns out there. Right now homemade water guns are mainly an American (for lack of the word United Statesian) and Canadian thing.

[Spindoctor]

Hi again!

Yes, copper pipes are easy to get in Europe (at least in Austria) and they are quite cheap. I never welded before, but even if I would learn it, my main concern is that "special parts" like check valves are even harder to obtain.

Yesterday I was in some kind of machine market, were they had check valves made of metall, but they were very expensive and very very heavy. So not really an option.

Has anybody found a way to solve this problem in Europe?

If I can find the time, I will visit some kind of plumber store, but I don't expect to much of it yet...