OK, you confused me here.  When you say the measured flow rates are 20% less, and 25% increased, do you mean over the flow rate that you normally see when the engine is not running?  

        Yes,  I used to see approx. 19Hz from the flowmeter when running the single EWP at full flow on battery power only, however I now see approx. 15Hz with either of the 2 pumps running with the other off. But I see approx. 24Hz when I have both pumps running together.

        During engine operation (14vdc, system pressurized) I normally see ~22Hz with the old single EWP. This equates to ~45litrers/min. This is a calculated amount, not measured. I expect I may now see ~56liters/min with both pumps while engine is running.

        I should also point out that for proper flow measurement there should be a straight run of 10 pipe diameters upstream and 5 downstream. Due to space restrictions I had to install the second EWP 6p/d upstream of the flowmeter, which will undoubtedly have some effect on the readings. Whether it is significant and in which direction, I can't tell you? However for daily operations it will be irrelevant, as I'm only looking for a percentage of flow readout.

        Currently in front of me is the breadboard prototype of my LCD flowmeter to mount in the panel, rather than using a multimeter to display flow in Hz.

You have to really wonder how low it gets if one pump is seized.  Actually, I'm hoping that you'll wonder enough that you'll try it for us :-) 

        I'm curious as to this myself, but as I can't access the pump shaft externally to clamp it, I would have to insert something like a welding rod inside the casing to hold the impeller stationary. I'll consider doing this tonight if the weather prevents flying.

        This is my last night in the hangar, as the summer rates are over ($250+GST/month) and the winter rates begin ($900+GST/month) which is waaaay to rich for me. So it looks like I'll be tying down outside for $25/month. This will limit the amount of wrench pulling that I'll be anxious to do for curiosity sake. I'd rather just fly :-)

In other words, would you have 60% flow if the second pump seized, vs 20% flow if the first pump did? 
        Good thought, but I since I see approximately the same flow readings from either pump, while running alone, it doesn't appear to make much difference.

S. Todd Bartrim
Turbo 13B
RX-9endurance
C-FSTB
http://www3.telus.net/haywire/RV-9/C-FSTB.htm

        "Imagination is more important than knowledge"
                                        -Albert Einstein