: I have been called many things but never a zymolgist

Well, maybe you could work on that one, then! A fine homebrew beats anything you can buy!

[efficiency]
: That is what got me tinkering also. A Grand Canyon guide showed me a pump
: that was better than everyone elses, so I took it apart to see what made
: it tick. What I found was discs that were full of holes like a sink drain
: and the nylon neoprene plunger flap material that was precision cut,
: friction free.

Hmm. I think I've almost gotten that part of it right. See photo. Oh, that part being 'full of holes' and not being 'precision cut'!

: I ended up making one for a guide friend and one for myself. Then I could not
: resist making a stubby one out of 4" pipe. It is too heavy to be
: practical but if there is ever a contest, I am ready.

!! Too heavy? Because it's schedule 40 pipe? You also wrote of 2 1/2" pipe, but, heck, you've got to find the stuff before you can use it!

: I am not tinkering with pumps now but if I get back to it I will try putting
: one wrap of Carbon fiber around a plastic mailing tube to cut some ounces.

Hmm. Heck, it would probably still be lighter (not than yours!) with a couple of layers of 'glass. And it just so happens that I have a LOT of 'glass left over from my 'yaks...

: The flap material is nylon neoprene from a military surplus dry bag vintage
: 1964. If you would like a piece of the material send me an address.

Thanks Reg, but I'm pretty set now for material. I'm experimenting with a beefy vinyl fabric and with vinyl underlayment for shower stalls. (Just in case you're curious, I plan on using the shower underlayment in the construction of my bulkheads... You never know - it might just work!)

Now, in the photo we have:
1: the pump as described on shawn's web site
2: the bottom clapet - same for shawn's pump and my modified pump
3-4: my plunger clapet. It is 1/16" or so smaller than the id of the tube. It has two bits of rubber/vinyl. One is just barely larger than the id of the tube. It is glued to the plastic disc and has holes that match those in the disc. It should allow water to flow through the holes as you push down and help seal around the edge. The second piece of rubber/vinyl is the same as for the bottom clapet and serves the same purpose as that one.

In the second version (not shown) I did use a street elbow at the exit (as per your idea). I found it helpful to shorten the 1/2" pvc pipe a bit (it holds the plunger clapet to the dowel) and then the length of the dowel isn't 18" -> it's optimized to the travel (I'd have to measure it).

Anyway, my simple tests showed that my new design will pump out about 1/3 of a gallon per stroke (emptied around 3g in around 9 strokes) -> I guess it works!

cheers!
charles

ps: yeah, yeah. Sure I could take better photos... Um. Maybe. Someday.