At first glance, it's not necessarily intuitive.

On the upstroke, the upper flap should be relatively "stiff" and push water out the discharge tube. This is also the intake stroke, and the bottom flap "flows" up around the edges and admits water.

On the downstroke, basically, the plunger is just getting pushed down into the water in the pump, and no water is moved in or out of the pump. The upper flap lets the water flow past, and the bottom flap seals to keep water from being forced out the bottom.

Remember that the pump is shown in a horizontal position in the photos--not the use position, which is handle-up.

If it still doesn't make sense, just try building one--it will work, trust me! :)

Also, mounting the pump below-deck will make it less prone to being stolen by a rogue wave. Don't worry about breaking the sprayskirt seal to get at it--you probably won't need it unless you're out of the cockpit anyway.

My pump mount: http://www.missoulaconcrete.com/shawn/kayak/cockpitinside.jpg

Shawn

> I had to think about how this pump works for quite a while before I
> understood it. Is it possible that something is reversed in the
> instructions for cutting and placing the two pieces of inner tube?

> I may need to build one of these since I lost my commercial pump on a trip
> last summer.

> Mike