How do two stroke pumps work? I'm talking about the ones where you pull out and water goes into the pc, and the same when you pull in, except from the other side of the pump. Does it use four check valves? I read somebody talking about it only needing two, but I don't know how that works (at least with how I think they work). And how do PreChargers pump air and water?

Double-stroke pumps only need 2 check valves, that is, if you make a good design. I will make an example using your own PVC program, just give me time to make the a design...



^That should work. If it doesn't, I will try to think back to how I designed a double stroke pump a long time ago that did.

Hmm.. I don't see how that would work. When you pull the pump one way, the water would rotate in the pipe. When you pushed it the other way, it would rotate the other way.

You are right. You need 4 check valves.



I made that a while ago...
Tell me if you need a better explanation.

Ok, that makes sense. How do PreChargers work? It is a two stroke pump, one side pumping air while the other pumps water, like this?

That's not how they work, but that's an interesting concept. Once you fired the air behind the piston would be stuck, though.

http://www.geocities.com/m15399/prechargesystem.html
^That's how they work.

I know the air goes in the back and the water goes in the front, but I don't know how it gets in there. Is it pumped, or sealed off, or what? :huh:

Oh yeah, now I remember. m15399's drawing is the way I set it up last year. Although you do not need 4 check valves. You need 3, if you bring the top of the left side around to the top right and then up. In the same way, bringing the bottom left to the bottom right via Ts allows you to have the reservoir attached to only one pipe, like normal. I'm at school in a free period, so I can't draw that now, I'll have to do it later.

No, I'm pretty sure you need 4 check valves--otherwise, the water would just circulate between both chambers. However, Duxburian, I'm interested in seeing your method for using just 3 check valves.

As usual, Duxburian posted a tracked pump design--which won't work in this case. Why? Because the slots will now leak water unless you have the two chambers separated greatly, which will make the design three times as long as it needs to be--x units long for chamber 1, x units for the track/pump, and x units for chamber 2. It seems far too inefficient.

Check out my design for the "Two-Stroke Pump" thread over at SSC. Trust me, it's the most efficient and practical way to do this...


PreChargers work in a completely different manner. Basically, a horizontall, cylindrical PC is split into two by a sliding plunger. One chamber is filled with air, and it needs its own set of tubes to be pumped up; BBT's PreChargers use the same pump for both the water chamber and the air chamber, and while this is great, it can cause a mess as the seals aren't that good and the water leaks now and then. The "PreCharger Homemade" thread at SSC contains lots of documentation concerning PreChargers, both commercial and homemade.

It would be hard to have a hole in the front for the shaft to go through. You'd need an o-ring to do that, which shouldn't be too hard, but the problem would be when pushing the piston back out, as the o-ring would be stuck farther down the shaft unless you stopped it somehow.

Actually it would only be 2 times as long as the combined length of the water chambers.
Let x = the length of one water chamber.

x + x = combined chamber length
2x = combined chamber length

in a tracked pump, the shaft needs to be as long as the chamber length being utilized.

Therefore track length = 2x

total length = combined chamber length + track length
total length = 2x + 2x
total length = 4x
4x / 2x = 2
Therefore the total pump length is only twice as long as the chamber length, and in conventional (1 chamber, non-tracked) extended pumps there is also a total length twice as long as the chamber length, so its not comparitively "longer than it needs to be" when compared to conventional pumps.

Duxburian, please draw what you're saying. I can't seem to picture what you're talking about or think of a way that uses only 3 check valves.

I haven't been talking about Prechargers, just two stroke pumps in general. A 3 check valve system should work for an APH design. And the tracked pump will work, since in a typical APH pump set-up, neither O-ring will reach far enough out to let water leak. Also, as Some Guy pointed out, tracked pumps and non-tracked are the same length. The non-tracked may be much shorter in the drawn in position, but are the same when fully extended.



^That might not work, I don't know if the water will travel back into the pump or not. However, since the check valves are drawing water in, the pumped water should be forced to the third check valve and where you want it, simply because there is no room for it to circulate back into the pump.

That will cause circulation. When you push the pump one way, the water will just flow around to the other side.

I think there's no way to do it with less than 4 check valves. :(

Wouldn't the incoming water being drawn in fill the space that would have been taken by the water that wants to circulate and force the would-be-circulating water to the third check valve for lack of other directions to go?

The incoming water wouldn't necessarily be drawn from the check valve. It would more likely be drawn at least half from the water in the other side of the circle. The water that you PUSH would be more likely to go around the circle than to go through a check valve (I believe check valves require a minimal amount of pressure to open, but it could be the opposite). You might be able to get some water in the PC, but once pressure built up, the water would take the path of least resistance and go around.

regarding 3 check valves: If anything, the check valve will require at least some slight pressure difference to allow water to pass in. There is no pressure difference required for the water to circulate, so it would just pass back and forth between the two chambers. Even if this did work, it would be an unreliable and to some extent pointless solution.

regarding a tracked two-stroke pump: I'll post a picture that explains my opinion soon.

EDIT: Okay, here we go:

Basically, it's a complex workaround that'll get you a tracked pump. The problem is that if you have a track in the middle of a two-unit (as opposed to three-unit) long pump tube, the water will just leak out through the track's slit. It's a better idea to have a wider tube that doubles back on the old one, trombone-style.

This is a good idea, but would be hard to implement. The actual pump would have to be either short, or the entire pump casing extremely long, in either case causing a dis-advantage. Flexible tubing would be needed to bring the water to the front check valve, and some sort of stopper would be needed isnide the pump tube, to stop you from overextending the pump past the slots in the PVC where the pump slides (in a tracked pump design). I'm more interested in the precharger design. This is a really good idea. However, the problem of getting the piston to slide back would need to be solved.

@ Some Guy: As I explained in the thread over at SSC, the O-ring is held place by the very edge of the male threaded fitting and by the back of the female threaded endcap.

@ wetmonkey442: Actually, I was just proving how difficult making a tracked twostroke pump would prove to be. Those slots would certainly cause some leakage, and getting around that is a mess, too...it makes the whole thing longer and needs a ton of tubing, as I demonstrated. Flexible tubing isn't actually required, but it would definitely make it lighter and easier to work with. Also, the "stopper" isn't need--the bar that goes through the track serves as a stopper anyway.

If it leaks, it won't work. The water will just go out the cracks instead of into the PC (because more pressure is required to get into a high pressure tank). If you look at my design, you'll see that it doesn't leak.

Its a four unit long pump, but since 2 units are water compartments the ratio is 4:2 or 2:1. Since an extended conventional one stroke pump also has a 2:1 length-to-water ratio. It would be like a normal tracked pump, not leaking, but longer.

I see how that would work.

Hmm...I didn't notice it, but m15399's design, at least with those proportions, will work. Unfortunately, it is like the others in that it truly wastes space, and mine is somewhat more efficient. Then again, mine is more complex, and can be obtained by using a larger diameter version of m15399's design...

It would not leak, as you would have the common sense to have the middle point-end points distance be shorter than the distance from the center to the O-rings on the pump shaft. Makes perfect sense, at least to me, since all it requires is doubling the normal tracked pump in the inverse direction.

I do see your point about it not being efficient, although if you want to get into that, I bet a normal pump with a larger ID would be more efficient than a double-stroker, since you would not have to alter the design for that.

I am actually going to try a homemade with a non-tracked pump just for the hell of it. I'm interested to see what it is like not having a track.

Well, as I drew the latest drawing, I was under the impression that you need to chambers to be able to use both strokes. However, that gives a total of four chambers, which is completely unnecessary, so I'm glad m15399 cleared up the confusion with that. If you're trying a nontracked pump, you might want to try to make the first homemade two-stroke pump. It should be easy, as long as you're up to cutting a hole in an endcap for the shaft to go through, though that shouldn't be too hard...

Why would he need to do that? With a two stroke pump you don't need endcaps.

You will need at least one endcap in all layouts. The required endcap is, to my knowledge, the most appropriate and the easiest way to secure an O-ring that is attached to the external tube (as opposed to the internal shaft). You're going to need to prevent water from leaking out the opening that the shaft uses to enter, even if that opening doesn't use an endcap. My solution is to use a male-threaded fitting and slide the plunger through. Then, lay a washer onto the circular face, lay an O-ring on top of the washer, and then screw on an endcap with a hole driven through it to hold the O-ring in place. This is an extremely reliable solution.

You've lost me. :P You don't need an endcap if you secure the O-rings to the internal shaft, something which works WITHOUT LEAKING. I don't know where you are getting the leaking from, because it doesn't happen with properly sized O-rings on a properly sized pump shaft. The hole the shaft goes through is NEVER empty, since part of the shaft fills it at all times. Maybe we make our pumps a lot differently? I don't even see how a double stroke pump even functions without using a track in the first place... :blink:

Well, by leaking, I meant when you're not using any O-ring at all--basically, the standard non-tracked pump. I'll take your word for it, but I don't think it's at all possible to secure an O-ring to the inside of a tube, as you'd need more space to work in.

You can use O-rings with non-tracked pumps. How else would you create the seal? If you used wrapped tape, it would leak a lot. Non-tracked pumps also usually have the O-ring attached to the pump shaft. In fact, the only differences between the two are the use of a track in tracked and the use of a washer and/or end cap in non-tracked. In a non-tracked pump, as long as you have the end cap or washer stop the pump from being extended so far that the O-ring comes close to the opening, it can't leak.

I finally understand why you don't understand the concept that I'm trying to get across...

Take a look at my first diagram. If you want to use the chamber that is farthest from the user and that doesn't exist in one-stroke pumps, you'll have to attach an O-ring to the inside of the encasing tube to prevent the water in that chamber from leaking out. In one-stroke pumps, there isn't any water there in the first place, so that isn't a problem. In this, an endcap is used to clamp an O-ring onto a male-threaded fitting, and you can't use tape or anything to put an O-ring inside a tube the normal way.

Oh, now I see what you're talking about. Although, isn't there a better way to make a double stroke non-tracked pump so you wouldn't have to do that? What about a symmetric pump shaft [pump extends out both ways, could still be held at one end only] or something like that?

Then again, it might be more worth it to use a dual stage or larger ID pump with less hassle.

If you're talking about having the shaft go all the way through the enclosing tube, I don't see how that would help--in fact, it would just make the whole design more complex. However, I think the method I've been outlining is quite simple and elegant--for such a performance boost, at least.

I plan on using a pump diameter of at least 3/4", especially in two-stroke pumps but even in standard ones. Remember, if one makes the pump shaft wide enough, it can take up a decent amount of space in the farthest chamber, so you won't be struggling too much.

People might get scared when they see the wood pump shaft soaked as they extend the pump... :D

Well, that's why wood shafts don't work well with this design, since they have to pulled out after use, or coated with a protective substance, so as not to rot. Aluminum would be a better pump shaft material for two stroke pumps. That is, if you can find any for good prices and have a decent drill press. I had a regular old hand drill that wasn't very powerful. When I get a new one, it should be able to drill through metal rods rather than the wooden ones which I use now.

Actually, I think I have a 12-inch steel rod somewhere...perfect! However, it's incredibly heavy, so I'll probably have to resort to using aluminum. I'll see what I can get, so thanks for the tip. I'll post it at the SSC thread if you don't mind...

It's Ben's tip, actually. The only reason I've been using wood is that it is dirt cheap and that my old drill wasn't strong enough to drill through metal.