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Last year I tried an
experiment placing two EWP's in series, and found that as expected there was a
~30% decrease in flow when only using one pump and flowing through the
unpowered pump (versus a single pump installation) and an ~50% increase in
flow when using both pumps. (data is from my memory).
It was consensus that a parallel installation would be the better way to
go, but would require check valves which are heavy and restrictive, soooo I went
about designing and build my own T/flapper valve. See attached
pics.
I
found that there was enough back-flow leakage or restriction that my flow rate
with a single pump running it would flow with a ~50% decrease over a single pump
installation and with both pumps running ~10% decrease in flow rate. During
ground runs it still cooled adequately, but certainly not as good as a single
pump installation. I was going to switch back but really felt I should at least
give it a flight test. During my short flight, coolant temps reached 230F and
oil temps reached 220F, but while this likely contributed, I don't feel it was
the sole cause of my troubles. (more on that later)
Clearly this wasn't the solution, but it was my affordable attempt to
build a lightweight aluminium Tee/flapper valve to allow parallel pumps.
Existing valves are too heavy and restrictive, so I feel the only way this could
be achieved would be if the manufacture could be persuaded to build a pump with
a built-in, non-restrictive check valve. Until then it seems the best way to
have dual pump redundancy is to place them in a series
installation.
Another piece of silver lining.... after the engine died,
both pumps continued to recirc coolant to allow for a better cool
down.
Ps. The pics may
look like they were an uncoordinated mess, but the main pump was securely
mounted low on the FW, while the spare was mounted to an engine mount tube. It
was difficult to route short direct hoses through
everything.
S. Todd Bartrim
Turbo 13B RV-9Endurance
C-FSTB
http://www3.telus.net/haywire/RV-9/C-FSTB.htm
"Whatever you vividly imagine, Ardently desire, Sincerely believe in,
Enthusiastically act upon, Must inevitably come to pass".
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