I was searching around the net and I came across this company that makes flow meteres that do not use any imepeller or blades to get flow rates. Which as many of you may know is quite an improvment over the flow meters that use a spinning prop moved by the water to measure the flow rate. These meters would cuase a heck of alot less resistance to the flow of the system than the other type..
anyway, here is a link to the companies flowmeter products.. apparently there are flowtubes (the sensor itself) and the flow transmitter, which collects the data.
http://www.foxboro.com/us/eng/produc.../flow/flow.htm
Bill will know alot more about this than I do and might be able to shed some light onto these flowmeters