> Did a fair amount of research on this a month or so ago. Like some other
> responders, I wanted to retrofit an old Henderson Chimp deck pump to serve
> as a foot pump, but found that finding a suitable stainless steel spring
> to fit inside the pump body was very difficult; stock on the Chimp foot
> pump is a conical expansion spring, about four inches high, three and a
> half inches diameter at the base and one and a half inches diameter at the
> top; don't know how it's measured in terms of stored energy force or the
> gauge of the wire, and that's the problem).

Great post, Jack. The only addition I have is about the spring question, which is moot if you don't use the Chimp, but may apply to others as well. The return spring fills the pumping chamber after you empty it with your foot, so the force it needs to overcome is the sum of the internal friction of the pump and the weight of the water column in the pickup tube. Internal friction is pretty small, so the major factor is the head pressure in the water column. Imagine having to pump out a deep hole with a pump mounted on the top edge. At some depth, the weight of the water in the pickup tube, and the head pressure caused by the difference in level between the top of the siphon column in the pickup tube and the top of the puddle you're trying to pump will equal the force generated by the return spring, and it won't pump at all. At shallower depths it will not work as efficiently or as fast. Head pressure rises at the rate of about .4 psi per vertical foot, which can be significant in a well but not in a kayak. So, it doesn't take much of a spring at the depth of 1 ft. or so to make it work quite nicely. BTW, phosphor bronze springs probably last longer than stainless in saltwater applications.