Granta - my copper APH (design phase currently)

Homemade water gun threads that are notable.
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cantab
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Granta - my copper APH (design phase currently)

Post by cantab » Sat Jul 12, 2008 8:15 pm

OK so I'm planning on building a copper aph soon, codenamed 'Granta' (after the old name for the river Cam).

Here are some of the design ideas I'm considering:

PC's: I could use a 2l bottle, but I'm wondering if it might make the gun a bit unweildy. So I'm thinking about smaller bottles, 330 or 500ml, possibly two or three of them in a line. That should also help flow, since the ID of the bottle tops is the same (22mm)

Pipework: I'd like to use 28mm from the PC to the nozzle. However if I just have a single PC then there's little point since the bottle neck is narrower. I'll probably use 15mm from the pumps to the PC.

Connections: I'll probably use compression fittings. Bulkier, but for my first gun, I don't fancy trying to learn to solder plumbing just yet. If the gun works out well then maybe the 'Mark II' will use soldered joints.

Pump: The only thing I'm not confident about how to do. I'll probably use 15mm pipe and I know where it's going, but other than that, advice please?

Layout: The PC's will come off tees from the main barrel. I'm not going to try any fancy bending for this gun (in part because I think it will compromise ergonomics).
I'd like the pump to be right beneath the barrel. To accomplish this will probably require a sort of J-curve in the pipework: from the pump, you have elbows going down, across, up, and then the tee to the reservoir and barrel. It's not part of the PC-nozzle stretch so the bends don't matter, and I think it's a great way to give the gun a fairly nice handle, and I could put a trigger there if I wanted. I'll want to put something insulating round the pipe there so it's not cold to hold. I reckon tape like is put round tennis racket handles might work well for that.
I'll just go with a ball valve to start with.

Reservoir: I want an onboard reservoir.
If I use a 2l bottle PC I'll probably use another 2l bottle for a reservoir. I'll have to live with it being screw-on I guess. I'll try and make it so the reservoir and PC generally balance each other about the handle (though obviously it can't always be perfect).
If, however, I use smaller PCs, then I don't want to undo that with a massive reservoir. Though I could use a bottle horizontally, with or without an intake tube (without, I'd put it neck rearwards so you aim up to pump, with the tubing going round).
I'm also thinking a milk carton could make a good reservoir (2 or 4 pint probably best). They have integral handles, so if I securely fix it to the rest of the gun it gives a nice way to carry the thing, or a fixing position for a strap.

I won't be getting the parts until the end of the month (when I can get money off at Homebase), but feel free to discuss. I might make some sketches.

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Silence
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Re: Granta - my copper APH (design phase currently)

Post by Silence » Sat Jul 12, 2008 10:04 pm

There's not much to say about building pumps besides that it takes trial and error. Drenchenator's guide details one method. It's more common to use tape layered around the rod on each side of the olive to hold it in place, and tape or a groove below the olive to increase or decrease the diameter. And don't forget lubricant. Beyond that, I don't have much advice, especially since I'm not too good at this myself.

DX/Duxburian had some threads about homemade soakers with reservoirs at the old SoakerMedia forums. Unfortunately, the linked images are no longer up, so there's little point linking to specific threads. Maybe he'll get the pictures back up sometime.

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cantab
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Re: Granta - my copper APH (design phase currently)

Post by cantab » Sat Jul 12, 2008 10:11 pm

Oh yeah - connecting 2l bottles to the pipework. Is it possible to get fittings that the bottles will screw into?

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Silence
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Re: Granta - my copper APH (design phase currently)

Post by Silence » Sat Jul 12, 2008 10:14 pm

According to aEx, 2 liter bottles use 3/4" FHT male threads. If you can find matching female threads, which may be difficult because of the Imperial units and non-standard threads, that would be ideal. Fortunately, Imperial doesn't seem to be fully phased out in the UK from what I understand.

aEx155
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Re: Granta - my copper APH (design phase currently)

Post by aEx155 » Sun Jul 13, 2008 2:01 am

SilentGuy wrote:According to aEx, 2 liter bottles use 3/4" FHT male threads. If you can find matching female threads, which may be difficult because of the Imperial units and non-standard threads, that would be ideal. Fortunately, Imperial doesn't seem to be fully phased out in the UK from what I understand.
Well, it is possible to use 3/4" FHT to connect to 2-liter and similar bottles, but unless you get the right kind of adapter, then it's going to be a bit hard.

If you go the route I did in my homemade, then you'll need to do some work. The metal fitting was smaller then some I've seen, so I had to file the threads off of the bottle, then screw the bottle in to cut threads into the plastic. It was a bit time consuming, but produces a small, clean connection.

An easier solution would be to use 3/4" compression x 3/4" slip, since the neck of the bottle just fits into the compression fitting. That's bulky though. and I don't know about PVC to copper connections.

I think the easiest route would be to use 22mm copper piping glued to the bottle neck as an adapter. It's a tight fit, and it should hold, assuming you get the right kind of epoxy.

There are a bunch of different ways to connect to a 2-liter bottle; some of the more advanced one's I've seen were when people cut threads into PVC fittings with special tools to make the correct thread spacing. You could also try gluing the bottle cap into a fitting, then making a hole, but that gets complicated.

I would recommend the way I used, with the 3/4" FHT X 1/2" MPT adapter, and two hose washers. It was the most secure, even though it takes all of the filing.
cantab wrote:PC's: I could use a 2l bottle, but I'm wondering if it might make the gun a bit unweildy. So I'm thinking about smaller bottles, 330 or 500ml, possibly two or three of them in a line. That should also help flow, since the ID of the bottle tops is the same (22mm)
2-liter bottles are fine if they are mounted correctly. If you put too many, or put them too far behind the hand area, then it makes it a bit odd to hold or balance the weight. If you go with this, I don't think you'll be disappointed, as it's cheap while still being a good option.

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Silence
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Re: Granta - my copper APH (design phase currently)

Post by Silence » Sun Jul 13, 2008 2:31 am

me wrote:FHT male threads
Whoops. FHT stands for Female Hose Thread, so I guess "MHT" would be the complement.

Tapping threads isn't possible without the right drill bit, and I'm not sure they would have the right size even at a hardware store. I remember the Lowes employees weren't very experienced with the machine, so demand may be fairly low.

aEx155
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Re: Granta - my copper APH (design phase currently)

Post by aEx155 » Sun Jul 13, 2008 3:21 am

SilentGuy wrote:Tapping threads isn't possible without the right drill bit, and I'm not sure they would have the right size even at a hardware store. I remember the Lowes employees weren't very experienced with the machine, so demand may be fairly low.
I think the people who tapped the threads used a lathe, with some kind of variable-spaced tapping machine-thing. I guess the turned the pipe/adapter to the right ID for the OD of the bottle thread area, then cut threads at the right pitch and space for the bottles to fit. They also had a rubber washer of some sort to seal the whole thing up.

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cantab
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Re: Granta - my copper APH (design phase currently)

Post by cantab » Sun Jul 13, 2008 8:08 am

I don't like the idea of cutting new threads into the bottle. It seems it will make it rather weak.
If glue will hold then that's the simplest option.

OK maybe 'unwieldy' was the wrong word. It's rather that I think 2l bottles are too bulky. I don't want my gun that tall.
And as I said, flow considerations are meaning I really like the idea of multiple PCs. But 4l of PC capacity would be a bit much I think.

devvo
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Re: Granta - my copper APH (design phase currently)

Post by devvo » Sun Jul 13, 2008 10:04 am

there are no fittings designed for plastic bottle threads, and if there was it would leak as they aint that watertight, the seal is made by that plastic thing on the inside of the cap, you should think outside of the box, if you want to carry on with the plastic bottle idea your best bet would be a tapered rubber laboratory stopper and bore it out to push in say a 15 mm pipe and then have some kind of strap to hold it on, or look to other containers as there are thousands of choices OR adapt the cap on the bottle, if it was me i would drill a hole in it, get some heP20 or similar plastic potable pipeing and use a solvent cement to weld the pipe to the bottle cap and then use a compression fitting on the plastic pipe extruding the cap

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cantab
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Re: Granta - my copper APH (design phase currently)

Post by cantab » Sun Jul 13, 2008 10:23 am

Ah right. So screwing the bottle in is no good then.

I could use a rubber bung like you say. However I know from experience that without further securing they'll only hold about 40psi, then the bottle will shoot off as a water rocket. The thing is also I'd like to keep the mouth as wide as possible, for performance. Pepsi used to use 'wide mouth' bottles, but not any more :-( Nowadays the only drinks that come in such are still.

Also remember I'm in the UK, plastic pressure-rated pipe is a pain to find, hence why I'm using copper in the first place. And solvent welding the pipe to the bottle probably won't work because most pipes are PVC while most bottles are PET; I think you can only solvent weld like plastics.

So I think I'll glue it to 22mm pipe. If the pipe fits - I think the figures for copper are external diameter, so it should.

Also, as a sidenote - I've noticed the major brands (ie coke and pepsi) tend to use thicker bottles than supermarket own-brands. So I'll bear that in mind.

Another sidenote - one probably COULD use champagne bottles. They're also designed for high pressures. Of course they'd be much heavier, more expensive, and more dangerous than plastic, so no-one in their right mind would.

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Silence
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Re: Granta - my copper APH (design phase currently)

Post by Silence » Sun Jul 13, 2008 1:19 pm

devvo: I think aEx's point was that drink bottles do use standard thread sizes - just ones other than what we're used to. If those threads adhere to the MPT standard, then there shouldn't be a problem, as long as you can find an FPT adapter.

cantab: Have you considered Gatorade bottles? They come in different sizes, but I know there's one size (in the US, at least) that is quite large in diameter but small in height. You also get the advantage of a wide mouth. Now that I think about it, that would also be great for enclosing spherical bladders.

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cantab
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Re: Granta - my copper APH (design phase currently)

Post by cantab » Sun Jul 13, 2008 2:03 pm

We don't have Gatorade over here, but we do have the similar Lucozade, which comes in the wide-mouth bottles. Thanks for reminding me.
Though actually, I'm not sure how wide. I am leaning towards gluing, because I think the connection will be strong by virtue of the glued area being quite large, and there being no corners which could concentrate the stress. And it seems simple. The only thing to watch for is using the right glue. Even if I do get it wrong, the worst that can happen is the bottle launches, which isn't likely to do much real harm, it'll just be like a water rocket.

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Silence
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Re: Granta - my copper APH (design phase currently)

Post by Silence » Sun Jul 13, 2008 3:02 pm

For the record, this is the type of Gatorade bottle I was referring to. I actually thought it was even shorter and wider, but I guess not. It may work as a pressure chamber, but I'll need to find something even shorter for a spherical CPS case. Maybe a Folgers coffee tub would work well, although it would be much harder to mount.

Edit: Then again, the hose barb takes up quite a bit of space. The Gatorade bottle might be better after all.

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cantab
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Re: Granta - my copper APH (design phase currently)

Post by cantab » Sun Jul 13, 2008 3:34 pm

I wouldn't advise using that for a PC actually. Gatorade is still, so the bottle won't have any pressure rating at all. Lucozade is a fizzy drink so the bottle will be designed to handle pressure. The Gatorade bottle would likely be OK for a CPS case, but not for air pressure.

EDIT: This:

http://members.lycos.co.uk/mickyonline/09890870.jpg

Is a panda pop bottle. Unfortunately, that's the old design; the new ones are narrower and taller, exactly what I don't want :-( ah well, i'm sure other small fizzy drinks bottles can be had.
Last edited by cantab on Sun Jul 13, 2008 3:42 pm, edited 1 time in total.

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Silence
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Re: Granta - my copper APH (design phase currently)

Post by Silence » Sun Jul 13, 2008 3:51 pm

Good point, although Gatorade bottles are thick. They're quite rigid. That said, it might just be very thick but weak plastic - say, polyethylene instead of polypropylene. I'm not too familiar with plastics, so I'm not sure. I'll check the plastic recycling code on the bottom when I next see a bottle.

A gallon-sized milk or water jug is the right size and shape, although perhaps a little large. The handle doesn't take up too much space. It's definitely not good for pressure, though.

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