Shadin Fuel flow

"Michelle P" wrote in message
ink.net...
Stan Prevost wrote:
I owned a turbo Saratoga with a Shadin, and have flown a lot in another
identical airplane with a Shadin. Work fine. One strange thing in both
airplanes is that turning on the electric boost fuel pump causes a
decrease in the fuel flow indicated on the Shadin, by anywhere from 0.1
to 1.0 gph. We spent a lot of effort in removing elbows, insulating the
transducer and fuel lines, relocating things, never changed it.

I always thought it was weird.

Stan


Stan,
Actually that makes sense. If you are pumping against the metering device
you will be initially raising the flow until the down stream plumbing
becomes "full". then things will slow down.

Michelle P

No, when I turn on the boost pump, thus increasing the fuel pressure to the
sensor and to the engine-driven pump, the flow indication decreases to a
new steady-state value until I turn it off, then it increases again to its
former steady-state indication. If I turn it on again, it decreases again.
Appears to be something unique to that sensor type since it does it in both
airplanes I fly that are equipped with the Shadin system.

Higher pressure giving lower flow indication is what is wierd. Actually, we
would like it to not change.

"Stan Prevost" wrote:

No, when I turn on the boost pump, thus increasing the fuel pressure to
the sensor and to the engine-driven pump, the flow indication decreases
to a new steady-state value until I turn it off, then it increases again
to its former steady-state indication. If I turn it on again, it
decreases again. Appears to be something unique to that sensor type since
it does it in both airplanes I fly that are equipped with the Shadin
system.

What kind of sensor is it? It's a turbine type, right?

Higher pressure giving lower flow indication is what is wierd. Actually,
we would like it to not change.

Interesting problem. Perhaps the higher static pressure is putting some
kind of friction load on the turbine shaft, maybe by deforming an o-ring
seal or some such.

--
Dan
C172RG at BFM

"Dan Luke" wrote in message
...

What kind of sensor is it? It's a turbine type, right?

It is a rotary sensor, but I'm not sure it is a turbine. Some type of
positive-displacement paddlewheel design.

Higher pressure giving lower flow indication is what is wierd. Actually,
we would like it to not change.

Interesting problem. Perhaps the higher static pressure is putting some
kind of friction load on the turbine shaft, maybe by deforming an o-ring
seal or some such.


Something like that is all I could theorize, also. We suspected for a while
that we had bubbles giving abnormal high readings, and the increaed pressure
from the boost pump prevented the vapor bubble formation and thus lowered
the readings, but we did about everything that we could think of to
eliminate bubble formation, to no avail. I concluded it was the sensor
itself.