On Wed, 12 May 2004 22:47:18 -0700
"Haywire" <haywire@telus.net> wrote:

> 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".
>
>

Hi Todd,

Could you sketch what your flapper valve looks like inside.  I expected
to see one flapper per pump.  

I think it makes sense that you don't get much more flow rate with the
pumps in parallel.  Using an electrical analogy, in series, the pumps
are increasing the 'voltage' (pressure) which will increase the
'current' (flow).  Neglecting the losses caused by the one way valves,
putting them in parallel reduces the'source impedence' or the resistance
to flow caused by the pump itself.

Bob White

PS:  I joined the list last week.  What a great list.  I've been working
on my rotary installation for over a year.  I don't know why it took me
so long to find it.  Great resource!


--
http://www.bob-white.com
N93BD - Rotary Powered BD-4