Dual Pumps Required?

[EDMO 1078]

I see from Suberavid's posts that he uses two fuel pumps for his Soob engine.  Since we have gravity flow from the high-wing tanks, I am wondering if two pumps are required.  I would expect from his bush flying in Alaska, that he would want a back-up pump, but is it required to pass airworthiness inspection?  The Soob engine does not have a mechanical pump in the engine.

EDMO

Edited 17 Jan 2016 by EDMO

[1avidflyer 1983]

I doubt that a fuel pump is mandated to pass an airwothiness inspection unless the application requires it.  Champs and Chiefs and how many other certified planes don't have a fuel pump.  Jim Chuk

[EDMO 1078]

I doubt that a fuel pump is mandated to pass an airwothiness inspection unless the application requires it.  Champs and Chiefs and how many other certified planes don't have a fuel pump.  Jim Chuk

I understand that part about the factory planes, Jim - What I was asking was that IF you have a fuel pump, do you also have to have an AUX  or back-up pump?

EDMO

[akflyer 1427]

The short answer is no..  Many of the Avids flying only have the mechanical pump and no back up electric pump.

 

[thebriman 69]

I added a backup facet electric.  I never use it, only check its operation during preflight.  410 hours on this Avid, 200 mine and zero issues with using only the Mikuni pulse pump Rotax supplies.  But the electric is there if I were to need it.

Edited 17 Jan 2016 by thebriman

[EDMO 1078]

I have a gold series Facet pump, but I would have to add checkvalves and more plumbing to add another pump - that's why I was asking.  If I was flying in the bush in Alaska, I would add the 2nd pump and not bother asking about it.  Some of these Facet pumps have the checkvalve to prevent reverse flow built into them, but mine don't.

Thanks to all,  EDMO

Edited 17 Jan 2016 by EDMO

[dynomike 91]

my plane will cruise with no pump but will not run wide open without it .I also have a secondary pump .I also leave one pump switch on when I shutdown just in case I forget when I fly next ,all down at shutoff ,back up with the one.

[EDMO 1078]

my plane will cruise with no pump but will not run wide open without it .I also have a secondary pump .I also leave one pump switch on when I shutdown just in case I forget when I fly next ,all down at shutoff ,back up with the one.

Thanks Mike,  I will check fuel flow, and pressure, both on gravity and with the pump - If both are OK, then I wont worry about it.

EDMO

Edited 17 Jan 2016 by EDMO

[dynomike 91]

what carb or carbs are you going to run ed?

[EDMO 1078]

what carb or carbs are you going to run ed?

Mike,  Right now I have a Holly 5200 (2 to 6 lbs required pressure) - but depending on cowl fit, and bank account, thinking about the AeroVee thingy, but don't know what pressure it needs.

EDMO

Edited 18 Jan 2016 by EDMO

[IFMT 36]

My soob with Holly carb has 2 facet pumps in series. Only one is running at a time. Has independent switch to each pump. Fuel flows through the non running pump no problem. Being that the carb sits quite high on the EA 81 there might not be much gravity feed on climb out. Carb on continental and lyc is low below the engine. 

 

[Av8r3400 1177]

Remember, without head (fuel) in the main tanks, the header will not flow via gravity to the engine.  Climb or dive. 

Personally I wouldn't be comfortable without a backup to the vacuum driven pump on a two stroke.   That's a lot of your eggs in one little basket...

[akflyer 1427]

I have had to use my electric pump twice in flight and both times it saved my ass.  Not due to failure of the mechanical pump, but do to tiny fibers from the tank plugging off the screen that I could not see during the preflight.  The fuel filter looked clear and fine to me when I looked at it, but in flight I started noticing the fuel flow dropping.  I hit the electric pump and it gave enough boost to get me to a safe landing spot where I was able to clean the filter and then continue on.  It really is pretty cheap insurance on the off hand chance that you need it...

 

 

[SuberAvid 617]

I installed the second fuel pump as a backup and ran them in parallel (since they have internal check valves this was pretty easy).  I only run one at a time and have never needed the backup yet.  Glad to hear Mike tried running w/o a pump and that it would a least run in cruise.  I intended to test that but never have gotten around to it.

[Luked 71]

Interesting conversation. Leni, you mentioned fuel flow dropping. I'm wondering if most people are using a fuel pressure gauge, or fuel flow meter, or both to keep tabs on this while flying.

[EDMO 1078]

My soob with Holly carb has 2 facet pumps in series. Only one is running at a time. Has independent switch to each pump. Fuel flows through the non running pump no problem. Being that the carb sits quite high on the EA 81 there might not be much gravity feed on climb out. Carb on continental and lyc is low below the engine. 

 

Good point - I had only thought about putting them in parallel - Just for info on the Facet pumps:  Some do not have check valves, and there could be a check valve that wont let fuel thru when the pump is not running, and some have a check valve to prevent reverse flow, and some may have both - be sure to read the specs before buying one, or installing one or two.  Now going to buy another one...

Suberavid - I believe I asked you to run the pump-off, or pumps-off, test a long time ago.  Hoping yours don't ever surprise you! 

Another note:  Spruce had a "Marine" fuel pressure gauge for something like less than $25 - good indicator to use if you don't want to spend the big bucks for a fuel flow system.

Keep the fans turning!  EDMO

Edited 18 Jan 2016 by EDMO

[akflyer 1427]

Interesting conversation. Leni, you mentioned fuel flow dropping. I'm wondering if most people are using a fuel pressure gauge, or fuel flow meter, or both to keep tabs on this while flying.

I use a fuel flow gauge.  If I am showing less than 7.2 gph on take off I know something is not right.  Cruise burn varies with altitude (a lot) but once I have it set, if there is not a drastic RPM change but the flow changes I know something is up.  The fuel flow meter I have is not longer made (navman 210)

 

 

[Luked 71]

Was it expensive? The least expensive fuel flow setup I can find on ACS looks like about $311 (UMA stand alone gauge with EI transducer). Fuel pressure gauge is about $77 for gauge and transducer (Vans).

[akflyer 1427]

The nav man, when it was available was around 189 bucks.  I wish I had bought a few more.  I may have to pull the one out of my boat and put it in the Amphib.

 

 

[EDMO 1078]

Luke,  the Marine fuel pressure gauge in Spruce is direct reading - just T's into fuel line - no transducer needed - Maybe why it is so cheap.

EDMO

[Av8r_Sed 82]

I'm using a backup electric pump which I haven't really needed yet other than to fill the carb bowls after maintenance.  I also have a fuel pressure gauge (1" UMA) with a Mallory Fuel Pressure Isolator so I'm not running a pressurized fuel line into the cockpit.  Wish I had a good fuel flow meter, but it's not worth hundreds to me.

[Luked 71]

I'm using a backup electric pump which I haven't really needed yet other than to fill the carb bowls after maintenance.  I also have a fuel pressure gauge (1" UMA) with a Mallory Fuel Pressure Isolator so I'm not running a pressurized fuel line into the cockpit.  Wish I had a good fuel flow meter, but it's not worth hundreds to me.

Sed, you must have one like this?  UMA 1-1/4 MECHANICAL FUEL PRESSURE GAUGES NON-TSO  If fuel pressure gauge has been enough for others, I'll probably just do that too. The flow gauges are pretty expensive. I have a friend with a carbureted RV-9A, and he just has a pressure gauge.

He used this gauge: Van's Series Fuel Pressure Gauge

[IFMT 36]

Just for clarity the thread has morphed into two lines. Those running two stroke/four stroke Rotax with the diaphragm pump that is standard and ED, myself and others with ea 81 conversion. There is no pump mounted on the subaru. I wouldn't think about flying an EA 81 without a fuel pump and a back up. I doubt there would be adequate reliable flow for an EA 81 to perform without. 

[Av8r_Sed 82]

I'm using a backup electric pump which I haven't really needed yet other than to fill the carb bowls after maintenance.  I also have a fuel pressure gauge (1" UMA) with a Mallory Fuel Pressure Isolator so I'm not running a pressurized fuel line into the cockpit.  Wish I had a good fuel flow meter, but it's not worth hundreds to me.

Sed, you must have one like this?  UMA 1-1/4 MECHANICAL FUEL PRESSURE GAUGES NON-TSO  

Yup, that's the one I'm using.  

[EDMO 1078]

I'm using a backup electric pump which I haven't really needed yet other than to fill the carb bowls after maintenance.  I also have a fuel pressure gauge (1" UMA) with a Mallory Fuel Pressure Isolator so I'm not running a pressurized fuel line into the cockpit.  Wish I had a good fuel flow meter, but it's not worth hundreds to me.

Sed, you must have one like this?  UMA 1-1/4 MECHANICAL FUEL PRESSURE GAUGES NON-TSO  

Yup, that's the one I'm using.  

For about $200 cheaper, I will stay with the boat fuel pressure guage.