Quote Originally Posted by MrToad View Post
Regarding pressure drop, the curve is in the third page of the manufacturer's brochure:

http://www.proteusind.com/500/500DS.pdf

There's two versions of the meter, being the one the OP is using the one with the highest flow rating (4.5 gpm) and the lowest pressure drop.

It curves from 0.75 psi @ 1.5 gpm to 2 psi @ 2.5 gpm.

The Fuzion (I had to go for a less restrictive block to make the comparison this time, because apparently when talking flow meters, the restriction is inversely proportional to the amount of money you fork out on the purchase) curves:

From 1.5 psi @ 1.5 gpm to 3 psi @ 2.5 gpm.

And the MCW60 curves:

From 0.75 psi to @ 1.5 gpm to 1.9 psi @ 2.5 gpm.

All these have been extrapolated from the graphs published by the relevant manufacturers.

So, restriction-wise is like have an extra MCW60 in your loop.
I connected a second flow meter in series with the first one (one after another), and the registered flow dropped by 0.2 GPM after adding the 2nd flow meter (from 1.31 to 1.11 GPM), which is somewhat close to the pressure drop you mentioned in the pdf (around 0.6 GPM drop at 1.3 GPM flow). Since I undervold my D4 pump slightly by powering it with a 20 watt rheostat to avoid excessive foaming/bubbling in the bay reservoir, the act of adding the flow meter to the loop will allow me to run the pump at full voltage, and hopefully the pressure drop due to flow meter will be offset by increased flow from pump running at full power.