Scout wrote:
Jeff,
I've no stake in this thread but I am curious. The pumps I've worked with
(granted they are not for marine use) don't provide much backflow prevention
when not operating. The rotary vane pumps (we used them for moving gasoline)
depend on centrifugal force (and sometimes small springs) to maintain a
reduced clearance with the housing (and also allow for some wearing of the
vanes). What is the nature of the pump to which you refer?

Smaller vane pumps are effectively positive displacement. The really big
ones like you're talking about aren't really PD. Also, most raw cooling
water pumps are described as vane pumps but the "vanes" are flexible
rubber molded with the hub, and instead of springing straight in and out
axially, they fold up as they rotate past the eccentric. This makes the
pump more effectively positive displacement, too.

That said, I wouldn't count on one to prevent backflow.

Fresh Breezes- Doug King