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RV-12 'AC' fuel pump

John,

Based on your experience with the pump, could you describe what would happen if the diaphragm were to tear? Would fuel leak into the engine or oil into the fuel?
 
Hey Dave - -

With this particular pump, if the diaphragm leaked, gas would come out the weep holes on the main body and fuel pressure could vary depending upon how much of a leak you had. If the shaft seal failed, engine oil would come out the same weep holes. The latest design has a drain tube to take whatever leaks to where you put the drain hose.

Note : The diaphragm is fairly heavy rubber in my opinion.

John Bender
 
John, good stuff!

If the supply side was pressurized would the diaphragm be trying to compress fuel? Can you see how running both pumps could cause a problem with his pump?
 
Hey Larry - -

My opinion is - - NO. The aux pump pressure is low, and I don't feel it would have any affect on the mechanical pump. The springs control the pressure of the mechanical pump output. The check valves are fairly sturdy I would say. You have just enough aux pressure to push past the check valves when the mechanical pump is not running, but that should not have any affect.

John Bender
 
After 1,200 hours fly a Rotax 912 I have never replaced a mechanic fuel pump. The only thing that changed was adding a fuel pump upstream. I added a switch to my -12 and I will see how long it lasts.

I think Rotax had an AD for running both pumps at the same time.
 
Hey Larry - -

My original pump started to leak fuel at the weep holes. I had to return it under warranty, so couldn't take it apart. I now have the same 'AC' pump I just took apart. It has been good so far. I would certainly believe the previous pump I had, and now the AC pump, and the latest, all work basically the same. My opinion is the aux pump should have no affect on the mechanical pump.

John Bender
 
Since you have been inside the pump...

Let me ask: Is there anything about the construction that would suggest there is any way the pump could perform intermittently?

I ask because I am hesitant to lay the blame for fluctuations in fuel pressure solely at the feet of the Dynon FP sensor. After 20 hours of solid FP readings after installing my replacement (old model) pump, I am getting very low indications on the day's first takeoff only. No alarms, just yellow; I take off with the fuel page front & center. About the time I get to pattern altitude the pressure creeps back in the green and then stays about 4 PSI. No power loss but I need to top off the adrenalin when I get back.

Jim
RV-12 264, 65 hours
 
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Hey Jim - -

My opinion would be - - NO. These pumps are not complex. If the aux pump is working when you turn on the master, then there should not be any change in what the mechanical pump is doing. If a tiny piece of 'dirt' got into the mechanical pump, it would not happen ONLY when you first started it up. I'd for sure try another sender, and/or check electrical connections. By the way, the screen on the inlet is super fine. Would be hard to get something into the valves that could cause fluctuations. Again, in my opinion.

John Bender
 
Geico266 said:
I think Rotax had an AD for running both pumps at the same time.
Click to expand...

Larry,
Like your old saying of "Without photos it didn't happen"...

With out a source it isn't true!



I have been through all of the Rotax Service Bulletins and have never seen anything remotely related to this.

Side note... considering that Eric Tucker (head Rotax Tech. Guru for USA) did an audit of the engine installation on N412RV at Sun&Fun just a few months before it received its S-LSA certification, I think he would have mentioned his displeasure of a full time electric boost pump with no switch to turn it off, if he thought it was a problem.
 
rvbuilder2002 said:
Larry,
Like your old saying of "Without photos it didn't happen"...

With out a source it isn't true!



I have been through all of the Rotax Service Bulletins and have never seen anything remotely related to this.

Side note... considering that Eric Tucker (head Rotax Tech. Guru for USA) did an audit of the engine installation on N412RV at Sun&Fun just a few months before it received its S-LSA certification, I think he would have mentioned his displeasure of a full time electric boost pump with no switch to turn it off, if he thought it was a problem.
Click to expand...

Think Larry was referring to the following,

http://rgl.faa.gov/Regulatory_and_G...67E5DA1704E1BA4186257727004C8C6D?OpenDocument
 
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rvbuilder2002 said:
Larry,
Like your old saying of "Without photos it didn't happen"...

With out a source it isn't true!



I have been through all of the Rotax Service Bulletins and have never seen anything remotely related to this.
Click to expand...

Sorry, it was an FAA Notice.

Thanks Marty!

Side note... considering that Eric Tucker (head Rotax Tech. Guru for USA) did an audit of the engine installation on N412RV at Sun&Fun just a few months before it received its S-LSA certification, I think he would have mentioned his displeasure of a full time electric boost pump with no switch to turn it off, if he thought it was a problem.
Click to expand...

Eric Tucker would not have known about the issue since the FAA published it May, 2010.
 
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Geico266 said:
Eric Tucker would not have known about the issue since the FAA published it May, 2010.
Click to expand...

The FAA issued their AD proposal because the European Aviation Safety Agency (EASA) had issued an EASA Airworthiness Directive 2007-0060R1-E, dated April 20, 2007 (the FAA AD specifically refers to it).

I am sure Eric was well aware of any issues relative to this, by May of 2010.

The documents say that the reason the EASA issued the AD was because of too high of fuel pressure at the carbs when an electric pump was used with the engine driven pump. The Rotax installation documentation say that the absolute max. fuel pressure at the carbs is 5.8 PSI or else the float valves can be over come and flood the engine.
The AD required checking the pressure and if it was too high, to replace the engine driven pump. If the pressure was not too high, nothing further was required. It never implies in any way that the electric pump should be replaced or removed all together.

If any RV-12 owner ever has fuel pressures that get near maximum (the D-180 displayed red line is 5.8 PSI) it should be cause for concern, but I am not aware of any that have come anywhere close to the limit.
 
rvbuilder2002 said:
If any RV-12 owner ever has fuel pressures that get near maximum (the D-180 displayed red line is 5.8 PSI) it should be cause for concern, but I am not aware of any that have come anywhere close to the limit.
Click to expand...

But can the sender be relied on to report the correct pressures ...?
 
N223JH said:
Let me ask: Is there anything about the construction that would suggest there is any way the pump could perform intermittently?

I ask because I am hesitant to lay the blame for fluctuations in fuel pressure solely at the feet of the Dynon FP sensor. After 20 hours of solid FP readings after installing my replacement (old model) pump, I am getting very low indications on the day's first takeoff only. No alarms, just yellow; I take off with the fuel page front & center. About the time I get to pattern altitude the pressure creeps back in the green and then stays about 4 PSI. No power loss but I need to top off the adrenalin when I get back.

Jim
RV-12 264, 65 hours
Click to expand...

Jim,

I am seeing the same thing in our 12. We are not using the same sensor as you (G3X just installed). The strangest part is that it only does it on takeoff. By 1000 agl, it is back up where it should be. I'll be doing more testing on this today, as I am leaving for Badlands next Thursday...I really hope to have this resolved quickly!
 
From FAA AD 2010-18-14

(d) This AD results from mandatory continuing airworthiness information (MCAI) issued by an aviation authority of another country to identify and correct an unsafe condition on an aviation product. The MCAI describes the unsafe condition as:
Due to high fuel pressure, caused by exceeding pressure in front of the mechanical fuel pump (e.g. due to an electrical fuel pump), in limited cases a deviation in the fuel supply could occur. This can result in exceeding of the fuel pressure and might cause engine malfunction and/or massive fuel leakage.
We are issuing this AD to prevent the pump from exceeding the fuel pressure, which could result in engine malfunction or a massive fuel leak. These conditions could cause loss of control of the airplane or a fire.

Actions and Compliance
(e) Unless already done, do the following actions.
(1) At the next maintenance, or within the next 25 hours of engine operation, whichever occurs first, after the effective date of this AD, remove affected fuel pumps, P/Ns 892230, 892232, 892235, 892236, 892540, or 892545.
(2) After the effective date of this AD, do not install fuel pump, P/Ns 892230, 892232, 892235, 892236, 892540, or 892545, on any engine.

These are direct copies of Rotax SB912-053 which also includes:

Checking and replacement of the electric (auxiliary) fuel pump
Check output pressure and flow rate of electric (auxiliary) fuel pump as per current ROTAX Instal-
lation Manual. Repair or replace any pump that does not meet requirements.

Both said it is imperative to replace the fuel pump....ours all have the new fuel pump...apparently however, they did not fix the problem. Simple as that.

Pete
 
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