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OOOOOOO,
A 35 A breaker--- for the pump???
Since the breaker is supposed to protect the wire from heat rise and
eventual fire, not the pump, that kind of amperage rating is appropriate for a
10 Ga wire for short periods of time (a 30A rating) or 8 Ga continuous (a
40A rating). The rating of wire is based on heat-rise, (I think it is 25*C in
bundled wire). The rating increases if the wire is well ventilated and not
bundled, or is overloaded for short periods of time such as smaller gauge, than
appropriate, used in a starter circuit. The heat comes from the resistance of
the wire to the electric flow. This resistance decreases with
decreasing Gauge.
Is he/are they really running that kind of wire to their pumps or do they
just uprate the breakers??? for possibly the wrong reason.
If the latter is true, and they use 16 Ga ( 10A rating) wire, as many pumps
are wired, if there is a high draw from the pump, for whatever reason in excess
of 10A but below 35 A, they may smell the toaster, not being aware of their
possibly fatal flaw. A dead short may blow the breaker first, but it may cause
various damages to the wiring bundle in which the pump leads reside.
If the main electrical trunk is protected by a 35 A breaker/fuse, that only
protects the main trunk, not the individual wires going to the pumps.
Rich
In a message dated 6/13/2012 10:32:56 P.M. Central Daylight Time,
hoursaway1@comcast.net writes:
I didn't
get a chance to respond to Ed's post yet. Yes they do have separate elect.,
pump 2 is set up on a 35A breaker with an emergency power circuit , by-passing
the master switch/solenoid & other elect., runs eng. only.
Thanks Bill, David.
From: "Bill Bradburry" <bbradburry@bellsouth.net> To:
"Rotary motors in aircraft"
<flyrotary@lancaironline.net> Sent: Wednesday, June 13, 2012
10:07:02 PM Subject: [FlyRotary] Re: Two possible causes was :
[FlyRotary] Re: Fuel presure question.
David,
If they don’t, each
pump should have its own circuit, otherwise you lose your
redundancy.
Bill
B
From: Rotary
motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Mark Steitle
Sent: Wednesday, June 13, 2012 8:24
PM
To: Rotary motors in
aircraft
Subject: [FlyRotary]
Re: Two possible causes was : [FlyRotary] Re: Fuel presure
question.
David,
Ed covered what I was thinking about a possible bad
check-valve in one of your pumps. And a bunch of other stuff I hadn't
considered.
Mark
On Wed, Jun 13, 2012 at 6:17 PM, Ed Anderson <eanderson@carolina.rr.com> wrote:
David, don't know whether you have
considered this - as you are aware the two pumps are able to work in parallel
because the pumps have check valves. So if one pump is off and the other
on, the on pump does not pump fuel backwards through the off pump. Since
each pump produces the 42 psi pressure by itself, one would assume the pumping
elements in both pumps are working properly. Also assuming the pressure
change is NOT due to a malfunctioning pressure sensor.
Here are some things that you
might want to consider:
1. That somehow when both
pumps are on - one of the pumps check valves is not closing properly.
Not a pump expert so not certain this could even happen - but the
thought occurred to me.
2. The effect of Increased
fuel flow rate due to both pumps may be causing a pressure drop
through an upstream orifice (like perhaps your "T").
3. Turning on both pumps
(assuming on the same circuit) might cause sufficient voltage drop in the line
sufficient to decrease the pumping performance of both pumps - pump flow rates
are sensitive to voltage variations.
4. The pressure return
regulator might be malfunctioning and opening due to the higher flow rate -
easy to check, just temporarily block off the return. If the symptom
disappears then it’s the regulator.
Theoretically, if the fuel flow
rate through the T's and pumps does not change with both pumps on, then
the pressure should remain the same - which is what you are expecting,
but not seeing.
So since the pressure does change
(drops) - what could cause this (assuming the pressure drop is real and not
the result some strange malfunction of your gauge)?
One thing that could cause
it, is if the fuel flow rate increases through an upstream orifice in
your fuel line (say at the "T" which feeds your two pumps) then the
pressure on the other (downstream) side will drop. Turn one of the pumps
off, the fuel flow rate drops, therefore there is less pressure drop across
this orifice and your fuel pressure on the downstream side of the
orifice will again go up.
Its similar to a resistor in a
circuit. The resistor value will remain static - the same, but if you
pull more current thought it, the voltage drop across it will increase
resulting in less voltage on the downstream side. Reduce the current
flow back to previous rate and the voltage drop across the resistor
decreases and therefore voltage on the downstream side
increase.
Another possible cause might be if
both of your pumps are fed off the same electrical line and there is
sufficient resistance that when both pumps are on the voltage drop causes less
performance by both pumps.
Just some WAGs that you might
consider, if the suggestions make by others do not result in identifying the
cause.
Sent:
Wednesday, June 13, 2012 6:43 PM
Subject:
[FlyRotary] Re: Fuel presure question.
Fuel is gravity routed from tanks
to ganged fuel selector out to T-fitting with each pump on the sides of the
T, to another T, into main line out to eng., pressure sender
is mounted directly after the T where the two pumps come
together. All this is in front of the wing spar near the floor in
an RV6A. This would make the pumps in parallel & the pressure is the same
from either pump, but both together pressure drops.
David
From:
"Mark
Steitle" msteitle@gmail.com
To:
"Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Wednesday, June 13, 2012 8:36:19
AM
Subject: [FlyRotary] Re:
Fuel presure question.
David,
How are your pumps plumbed... in
parallel or series? What kind of
pressure do you get when running the
backup pump only?
Mark
On 6/13/12, Tracy <rwstracy@gmail.com> wrote:
> Hmmmm... Mine
goes up about a pound when I switch on the second pump. What
>
happens when you turn both off?
>
> Tracy
>
> Sent
from my iPad
>
> On Jun 12, 2012, at 7:11 PM, hoursaway1@comcast.net wrote:
>
>> Question
about fuel pressure indications, at fast idle 2200 RPM, fuel
>>
pressure is 42 PSI on EM2, if I switch on the back-up pump with
the
>> primary pump the pressure drops to 35 PSI, can here both pumps
running, if
>> I switch off either pump pressure goes back to 42 PSI.
My system is 13B,
>> stock red injectors all four, pressure
regulator is stock Mazda on the end
>> of fuel rail with vacume
connection from dynamic chamber. Thanks, David
>> R. Cook
RV6A Rotary.
>
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