> A stronger spring will refill the pump body more quickly than a very weak
> spring, given the same system. This may be where I'm going wrong, as I'm
> not calculating time (horsepower) requirements. We want to pump quickly,
> so if we have to wait for the weaker spring to push out the diaphragm,
> then that's no good. I'm trying to optimize, that's all.

I'm no scientist, but I think that's where the problem comes in, Pete. I live near the industrial city of Baltimore and travel regularly to Norfolk; in each city, there are a few specialized spring manufacturers, and most have odd lot and scrapped lot springs lying around in ancient wooden drawers. They'll sell you a bag of nice stainless steel springs for five bucks! I think I must have tried five or six different springs inside my Henderson Chimp pump --- an attempted conversion from a deck pump --- and several did work. But very slowly, to the point of being useless. The inlet valve in my Pintail, the test vehicle, is about three inches above the bilge --- dunno how that translates to lift height --- and it's a low volume boat even without my conversions to optimize water exclusion. I could not find any aftermarket springs that worked nearly as well as the standard Chimp foot pump spring.

Guess it's a gray area in your hydronamics, Pete. Some springs will work, but not as well as others. In my book, if I have a flooded cockpit in open water, I want the water out quickly, and a little increase in the energy I have to put out to compress a spring to empty out the pump body is marginalized by getting the boat back to a safe and maneuverable state.

Good luck with the bungees. (Don't get your foot trapped!)

Jack Martin