Don't ask me! I stared at that clear plastic demo version for hours at the
boat shows trying to figure out how it works! When it finally dawned on me
it was incredibly simple but it takes some high class machining to make that
valve block. I can see why they cost so much. Even with a CNC milling
center it has to cost $300-400 just to mill out the valve block. I think
there are at least 3 WM makers offering Clark pump based systems now and
none of them will sell the pump without a full system.
At one time Spectra had an exploded parts sketch and a parts list with all
the o-ring dimensions that was enough to reverse engineer it but I think
they took it down after I pulled out my calipers at Annapolis a few years
ago to get a few last dimensions. :-)
The valving is similar to a Worthington shuttle pump used on steam
locomotives to feed boiler water but what makes it work is the piston rod.
The water on top of the piston is forced into the membrane. As it comes out
it goes to the back side of the piston to help push new water through but
the rod takes up about 6 or 7% of the cylinder volume so there is not enough
room for all the water to fit. It has to go somewhere so it is forced out
through the membrane.
What took more time to figured out is the system pressure. Ignoring
friction loss it should recover about 93% of the energy put in but the feed
pumps they use can only get to about 35-40PSI so I figure the system
pressure is around 600PSI. That is enough to produce some fresh water but
it is not enough to run the membrane at the nominal 12% recovery rate at
800PSI. Ran 600PSI through a SW30-2520 on my Filmtec simulator software and
come out with a 6% recovery which is about the displacement of the pump.
OTOH, gallons per amp hour is what counts so I guess driving the membranes
at a low rate is a non-issue. You just have to get used to the constant
clump-clump of the pump for hours on end.
--
Glenn Ashmore
I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at:
http://www.rutuonline.com
Shameless Commercial Division:
http://www.spade-anchor-us.com
"Skip Gundlach" wrote in message
oups.com...
Drop Glenn, of rutu fame, a note. I'm sure he has the answer....