Homemade using 2-liter bottles

[aEx155]

Pictures are up now, and soon to come is my new pump; this time, I used 3/4" tees instead of 1/2", and I used o-rings and this round metal thing instead of washers and rubber stoppers.

Pictures:




The pictures in order (left to right, down, then left to right again)

1. The pump ready to be cemented
2. A single check valve
3. One of the two "sealing things"
4. A "sealing thing" on top of one of the four 3/4" to 1/2" reducers
5. "sealing thing" inside 3/4" tee
6. Pump cylinder to tee connection
7. Pump cap secured with hose clamp
8. If you look closely, you can see two pieces of copper wire that serve as the stop for the pump

I just need to get the springs, some #8 o-rings and cement the whole thing together, then it'll be done. It's very similar to my original detachable pump; it just has bigger check valves. Hopefully it won't lag as much...

[aEx155]

I really hate to keep dragging this thread along, but it wouldn't make sense to make a whole new thread, so sorry for bumping (again).

Anyways, on to the update: I finally found a way to connect 2-liter bottles to PVC without having it leak at all. I figured that I needed some way to go from 3/4" FHT to 1/2" MPT, so I originally used the plastic couplers that you have thus far seen (if you've read the whole thread; if you haven't, you can go back to see what I'm talking about). The problem with those was the fact that they were two parts that snapped together; the weak point was the area they snapped together at. I then though about using some kind of barb to fit into the cap of the 2-liter bottles that I would glue into place. While looking for said barb, I stumbled upon a (one piece!!!) metal 3/4" FHT to 1/2" MPT adapter. I was like, "This is what I've been looking for!" (not aloud, as I was in Home Depot at the time)

I bought three, along with a pack of hose washers, and some other things [#8 o-rings, a 1" coupler and misc. parts for repairing my pump].

So, if you're looking for a way to attach 2-liter, or any kind with the same mouth size, to PVC, I finally found a secure answer (I'm very sure I'm not the first, though; I've read about others but they used things I didn't have. Rather than being custom made, I used something store bought).

In order to get the bottle to fit into the adapter, I needed to file practically all of the threads off of the bottle. I then put one more hose washer (the flat ones are the best) in the adapter (there was one already included inside the adapter) and carefully screwed the bottle into the adapter. Since it was metal, it cut threads into the bottle, holding it securely while making a good seal.

Now, the pictures:






Line 1: My mini-water gun; my hand held nozzle trigger assembly with a 2L attachment - a shot of the 2L/fill attachment - the male QD on the end of my pump; it works for filling up waterballoons, too - my repaired pump; you can see the 1" coupler in the lower left.

Line 2: The 3/4" FHT x 1/2" MPT adapter - my 3-bottle water manifold, with attached hose and one-handed hose nozzle - my 3 bottles attached with adapters - my pump cap (simple, isn't it? the cool thing is it doesn't come off...)

The rest of the pictures are just of my pump and the check valves:
Line 4: inside a check valve to look at the spring (I used 3/4" female threaded plugs this time, instead of 1/2" slip plugs) - a view of the front of one of the sealing faces

In the last two pictures, you can see ho I flattened out the back of the metal piece I was using to hold on to the spring; I'm not sure whether or not it increases performance, but it's a lot more like a real check valve than using marbles or tire valves.

Questions and comments would be appreciated; I'm happy to provide more pictures or to explain anything in detail if you want me to. If you can't figure out what parts I used from the pictures (or if you want to know what specific brand/part I used), then you can just ask me and I'll make a parts list if you want one.

[Ben]

Interesting and pretty simple. This is making me consider trying two-liter bottles for some cheap air chambers in some designs. With the low pressure drop design this could be very practical if it fits the form factor.

[Drenchenator]

Nice find, aEx155! I'm sure some people will find the part very helpful.

[Silence]

Good job. Would you mind if we repost the article in the homemades section? We could link to the thread too, but it deserves more and an article would be more direct.

[aEx155]

Originally Posted by SilentGuy

Good job. Would you mind if we repost the article in the homemades section? We could link to the thread too, but it deserves more and an article would be more direct.

An article would be fine. I'm glad all of this work to find a way to use 2-liter bottles as cheap pressure chambers is going to good use.

[aEx155]

Sorry for double posting.

I have a question about pump rods. Could anyone suggest something to try as an alternative to metal, while still being stronger than wood? I have a big problem with breaking pump rods, so if anyone can suggest a cheap alternative, that would be great.

I'm thinking a plastic rod/cylinder would work well, since that's what they used in regular guns; I haven't seen any in Home Depot though. Does anyone know where I can find them, without having to order?

Lastly, how easy is it to make a metal pump rod? I know that it's been done before, so I'm sure someone can help me on this. Do you use 3/8" diameter solid or hollow?

[Silence]

Wood should be strong enough...if anything, it's more solid than the plastic ones in commercial water guns. Not much will help a rod if a water gun is dropped with the pump sticking out, though.

If you have a metal rod, it's easy enough to work with. It doesn't matter if it's solid or hollow, but you will need to plug the end with epoxy or something if it is hollow. I'd suggest getting aluminum - it's lighter, cheap enough, and cuttable using a metal band saw.

Don't worry about double posting - that's only a problem after a few minutes and if somebody forgot to mention something.

[aEx155]

The problem I keep having with wood is that it keeps breaking. I don't know the cause (would leaving it soaked be it? I think so, but I'm not sure. I do let it get dry, though.), but so far, all but one pump rod as broken on me (I replaced it with another, after the o-ring seals started leaking too much). Wood has worked fine, but having to make a new one every time it breaks is a bit of a problem.

A few more questions:

Is there an easy way to increase pump volume? I know larger diameters make pumping harder, but if my math is correct, then 3/4" should be 26 lbs of force needed at 50 PSI. Does that seem like too much? (the way I have it set up (not the best) is that the pump is supposed to add about 3 liters (1/2 capacity) of water to my PCs. If I was able to get the full stroke on my 1/2" pump which is 18", that's 36 pumps to full, although I''m not able to get the whole pump length because of a few problems I've been having.)

My pump starts leaking at higher pressures (40-60 PSI), so I went from 1 o-ring to 3 to no effect (except that it leaked less). each o-ring can barely fit when I put the pump rod into the pump cylinder, but is there a way to fix this leak? (or is the pressure too high? I don't think it is, though)

[Silence]

Well, if you want to use a plastic rod, McMaster-Carr should have it in stock. Polypropylene should be strong enough, and I'm sure it comes both as rod and as pipe. Anything with 3/8" OD should work.

There aren't really any shortcuts when it comes to pumping - elbow grease is the only option. I would not suggest using 3/4" pipe (and remember, the actual ID is larger than the specified one) because, in my opinion, 26 pounds really is too much. A gallon of milk is 8.5 pounds. A heavy school backpack could be about 26 pounds. Lift it off the ground in a pumping motion and you'll see it's rather impractical to do too many times.

If you can't pump the whole length for fear that the pump will pop out of the tube, use a coupler on the end of the pump with a washer or something wedged between it and the pipe. A bit of duct tape should hold the coupler onto the pipe. If you can't find a washer with an ID large enough to let the pump rod through, cut your own out of any material. It doesn't need to be too strong.

Make sure you're using silicone lubricant (or even an oil-based one like Vaseline) to let the O-rings slide. Lube makes it easier to pump and improves the seal - so it kills two birds with one stone. If it becomes too easy to pump after lubing and there's still a poor seal, use another layer of tape below the O-rings to get to a better seal while maintaining low friction.

[aEx155]

Originally Posted by SilentGuy

Well, if you want to use a plastic rod, McMaster-Carr should have it in stock. Polypropylene should be strong enough, and I'm sure it comes both as rod and as pipe. Anything with 3/8" OD should work.

There aren't really any shortcuts when it comes to pumping - elbow grease is the only option. I would not suggest using 3/4" pipe (and remember, the actual ID is larger than the specified one) because, in my opinion, 26 pounds really is too much. A gallon of milk is 8.5 pounds. A heavy school backpack could be about 26 pounds. Lift it off the ground in a pumping motion and you'll see it's rather impractical to do too many times.

If you can't pump the whole length for fear that the pump will pop out of the tube, use a coupler on the end of the pump with a washer or something wedged between it and the pipe. A bit of duct tape should hold the coupler onto the pipe. If you can't find a washer with an ID large enough to let the pump rod through, cut your own out of any material. It doesn't need to be too strong.

Make sure you're using silicone lubricant (or even an oil-based one like Vaseline) to let the O-rings slide. Lube makes it easier to pump and improves the seal - so it kills two birds with one stone. If it becomes too easy to pump after lubing and there's still a poor seal, use another layer of tape below the O-rings to get to a better seal while maintaining low friction.

I was really hoping I didn't have to order from McMaster or anywhere else; do you think Home Depot/Lowes has something that would be a possibility? I've been to a large variety and I haven't seen anything that might work, so I'm not sure...I might just go with metal after all. (I was hoping I could avoid that because of the fact that my dad thinks I've spent too much money on this one project alone...mostly it was because I didn't get the right part the first time...I'd say it's approaching $140, even though I tried to make it as cheap as possible while still making the gun (not making it was always a possibility ))

Well, I got those dimensions from a link in the PVC reference thread, so I'm not sure whether or not they would be accurate, but I would guess they're pretty close.

The big difference between my pump and a regular, gun-mounted pump is the fact that it's closer to a bicycle pump than it is a gun-mounted pump. I sometimes use both hands to push the rod down, so I don't think that it would be the same situation; in a gun-mounted pump, you're pulling the rod in with only one hand, which brings up the force problems as you mentioned. (on the end of my pump, I have a 1"X1"X1/2" tee (with the center being 1/2") that I use as a handle for my pump. It gives me a better grip on it, and it works better for two hands)

My problem isn't the fact that I might pull the pump out; I have stops (electrical tape) so that the o-rings won't come out (just like anyone would). The problem with an extended pump is that it's really east to break the rod if it isn't strong enough. (imagine the difference between breaking 2" ruler in half compared to a 2' ruler)

My pump uses large amounts (maybe too much?) of Vaseline to seal the o-rings. Each are spaced about a 1/4" apart, and fit pretty tight, as I've said; I really can't figure it out...

[cantab]

So basically, a long wooden rod is breaking when you try and pump it? That's to be expected - long things break more easily than short ones when you compress them.

If you can use a thicker rod, do so.
If you're willing to shorten it, that will help stop it breaking.
If you put the extended length of the rod in an outer case that could also help. Pipe that's a close but loose fit should be fine, with one or two slots cut in the side to connect a grip through to.
You could use metal, but the risk there is it bends. You might get a slight bend that you miss until you shove it down and then find it jams.
Another way of avoiding the problem is to make a pump that works on the pull stroke. You can then use a much thinner pump rod. But that's more difficultt

[Silence]

Yeah, I have to say it sounds like you want a tracked pump. Duxburian used to use them in all his older homemades. Here's a rough outline of what you need to do:

• Shorten the pump rod to about half the tube's length, plus a couple inches. If you want a longer rod, you'll have to replace the tube.
• Cut a groove on each side of the bore from one end of the pipe to the midpoint. Make sure you draw the line first. And whatever tool you use, it's easier if you start at one end of the pipe instead of an inch from there.
• Drill a hole through the side of the rod, about an inch from the end.
• Stick a bolt or something through the hole and through the grooves.
• Slide the pump rod assembly into the tube.
• Attach some type of sliding handle to the protruding stubs of the crosspiece. 1" PVC pipe will probably work for this, as will any 1/2" fitting with sanded down innards or any 1/2" saddle fitting. A 3/4" fitting should work too. I'd recommend a wye or a cross.
• Use a 1/2" coupler or elbow on the end of the pump tube to hold the split pipe (thanks to the two grooves) together. An elbow makes it easier to support the tube because you can connect it to another part of the water gun. That's easier done if you've designed the water gun with a tracked pump in mind, though.

As for your seal...I'm not sure what the problem is. We don't even know whether the water is passing above or below the O-rings (ie, next to the PVC or the wood). Make sure the wood is dry before you stick it in - it may be looser then, which means more tape, of course. You could also sand a bit of a taper into the bore at the end of the pump tube to make it easier to stick the O-ring in.