Date: Thu, 13 May 2004 08:25:39 -0600
From: Bob White <bob@bob-white.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: EWP's in parallel
Message-Id: <20040513082539.636bdddc.bob@bob-white.com>
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Hi Eric,

That's what it looks like to me also, which wouldn't be the best
approach.  One pump will almost invariably pump a little more than the
other.  The one way valve needs to be set up to prevent forcing flow
backwards thru the weaker pump.  OTOH, with the single flapper, it might
adjust itself to balance the output from the pumps.

Bob White

On Thu, 13 May 2004 10:11:32 -0400
"Eric Ruttan" <ericruttan@chartermi.net> wrote:

> I thought it was one flapper hinged to flap to either side.
> So it would be hinged in the corner BETWEEN the two "pump in" sides.
> 
> This is was the premise for my post.  If it is incorrect, sorry.
> 
> From: "Bob White"
> > "Haywire" <haywire@telus.net> wrote:
> > 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!
> 
> > > 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.
> > >
> 
> 
> 
> >>  Homepage:  http://www.flyrotary.com/
> >>  Archive:   http://lancaironline.net/lists/flyrotary/List.html
> 
> 


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