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  #21  
Old 12-03-2016, 06:24 AM
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Originally Posted by DanH View Post
Sorry Don, missed your post. The 68,000 per gallon is from the EI datasheet for the cube:

Jon; sorry don't know anything about a FloScan. Anybody have a bad one to spare?
I might actually have a FloScan that we can dig into... I'll see if I still have it.
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  #22  
Old 05-10-2017, 07:54 AM
BillL BillL is offline
 
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Default A little insight

I have posted here as it relates to the "red cube". A recent post by Lan Vinh Do (http://www.vansairforce.com/communit...d.php?t=149243) showed he relocated his flow transducer to FWF downstream of the mechanical pump. This (along with other changes) stabilized his fuel pressures at altitude.

We have long talked about the fuel flow difference and the tiny pressure drop. While the pressure drop from end to end is relatively low, Dan has shown the flow area of the interior. A 3/8" fuel supply tube (.297" ID) at 12 GPH enters at ~11 in/sec, but accelerates to 49 in/sec in that small diameter. The Bernoulli calculator shows that this is a 0.08 psi change in local pressure. Maybe enough to cause bubbles if it is near the vapor pressure due to temps already.

I had hoped this calculation would give some insight as to why it is likely to result in fuel pressure issues at altitude (boost pump off) when located prior to the mechanical pump, but with the corrected values, it is only a small benefit. At least, now (with bubbleheads assistance) we have quantified this parameter.

Edit: The values above have been corrected - I missed a critical division by 12in/ft in the velocity and input the wrong values. Thanks to bubblehead for checking and sending me a nice email.
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Last edited by BillL : 05-10-2017 at 02:51 PM. Reason: A sharp VAFer pointed out a math error. Thanks!!
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  #23  
Old 05-10-2017, 09:14 AM
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Originally Posted by BillL View Post
Since the pressure is sensitive to flow rate, it also may indicate why the RV10 is more susceptible to this effect than other RV's
I suspect the big factor with most RV-10's is a hot tunnel containing several feet of fuel line, i.e. they are delivering warmed fuel to the transducer, greatly increasing vapor pressure.

Put another way, a stainless belly panel over 1/8" of fiberfrax would probably cure most of this stuff. Instead we see builders insulating the inside of the tunnel....
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Last edited by DanH : 05-10-2017 at 09:20 AM.
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  #24  
Old 05-10-2017, 02:14 PM
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Originally Posted by DanH View Post
When the cube is installed between a boost pump and the engine driven pump, most builders report an excessive fuel flow indication with the boost pump running.
That's exactly the case with my JPI EDM-700 fuel transducer which works on the same principle. Turning on the boost pump makes the fuel flow read 20% high. Matronics offers a Pulsation Damper which is supposed to fix that problem.
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  #25  
Old 05-10-2017, 02:53 PM
BillL BillL is offline
 
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Quote:
Originally Posted by DanH View Post
I suspect the big factor with most RV-10's is a hot tunnel containing several feet of fuel line, i.e. they are delivering warmed fuel to the transducer, greatly increasing vapor pressure.

Put another way, a stainless belly panel over 1/8" of fiberfrax would probably cure most of this stuff. Instead we see builders insulating the inside of the tunnel....
After getting a math lesson from Bubblehead (THANKS), you could be right, with the low velocity the fuel has some time to collect heat there, and a good bit of area. From one graph .1 psi is equal to 1 deg F in terms of vapor pressure, so with a few 3-4 seconds in the tunnel, it could be more than that.
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Last edited by BillL : 05-10-2017 at 05:32 PM.
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  #26  
Old 05-26-2017, 07:06 PM
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Default Flo-Scan Pulsation Damper

Quote:
Originally Posted by snopercod View Post
Matronics offers a Pulsation Damper which is supposed to fix that problem.
Two weeks after I ordered it, the unit arrived via UPS today but I'm not sure I'm going to install it. I was expecting it would have a bladder inside to dampen the pulses, but it's just a hollow SS sphere. The unit is supposed to be mounted with the sphere facing up so that the vapor in the sphere acts as the cushion.

After some consideration, I'm really not sure I want to add this device to my fuel system. It would have to be insulated so as to not warm the fuel. The Tee fitting that came with it would add two more places to leak. It would add more weight cantilevered off the 1/8" NPT pipe fitting on my Facet boost pump.

The problem with my fuel flow reading high with the boost pump on hasn't really caused any problems so I may just live with it. My EDM-700 fuel totalizer was only off by 0.1 gallon after the last 30 gallons I burned.
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  #27  
Old 06-03-2017, 03:18 PM
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Default Pulsation Damper didn't help

I went ahead and installed the Flo-Scan pulsation damper anyway, just to see what it would do. I tee'd it into the outlet of the Facet boost pump, and wrapped it with firesleeve for thermal insulation. I went flying with it today and it made absolutely no difference in the original "fuel flow reading high when the boost pump was on" problem. On climbout the fuel flow went from 10.1 to 11.5 with the boost pump on. At cruise it want from 6.5 to 7.1 GPH. I'll be removing the unit next time the cowling is off.
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  #28  
Old 06-22-2017, 08:43 PM
Timberwolf Timberwolf is offline
 
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Dan,

I have a floscan that is of no use and has been replaced with a red cube. I'll get it to ya when we meet up.
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  #29  
Old 06-23-2017, 07:14 AM
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Cool. We will sacrifice it on the altar of knowledge
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