RV12 - Trouble draining water from fuel tank

[mmahony1]

I have an RV12 and am having trouble completely draining water from the fuel when it has intruded into the tank.

I don't seem to be able to drain all the water in one glug as I'm used to when draining directly from the tank in other aircraft. Instead, fuel with a very small amount of water in it comes out continually as I drain. I can sample a gallon or more of fuel before water seems to be depleted. The total amount of water drained may just be a couple of tablespoons.

When draining I turn the fuel pump on, let it run 30 seconds or so, then drain from the gascolator. No water accumulates in the gascolator before sampling. Instead, water only seems to flow when fuel flow increases while sampling actually takes place.

My father, a retired airline A&P, suspects surface tension causes water to stick to the screen at the fuel line in the tank. His theory is that the increased pressure caused by higher fuel flow when sampling is enough to overcome the surface tension and pull water through this screen.

Any thoughts? Has anyone experienced or dealt with an issue like this in the past? Many thanks in advance!


As an aside, the plane lives outside. I suspect water gets into the fuel tank around a loose seal between the gas cap and filler neck and have replacement parts on order to rectify this.

 

[rcarsey]

I can't really speak to why its coming out in such small amounts.. but as you said at the end.. the real fix is to prevent water from getting in to begin with and avoid the problem completely.

 

[lr172]

I have never seen a 12, but have to assume it has tank sump drains. WHy are you not pulling the water there? Pumping it to the gascolater is going to mix it all up and will need to wait for it to settle out again. I thought it was standard practice to use the sump drains, as this is where the water will settle and why the designers put it where it is. The gascolater is only there to let small amounts of remaining water to settle out over time.

 

[Mich48041]

The fuel tank on the original RV-12 was vented through the cap. Don't block the vent.

 

[mmahony1]

Rob, yes agreed.

Joe, thanks for coming to point this out. I am very aware of the need for the vented cap.

lr172, in the 12 the tank is in the fuselage and there is no direct sump on the tank. Instead, the procedure is to sump via the gascolator.

 

[G JWTP]

Or thinking about this from a different angle, put in 3-4 gallons of Super Unleaded Mogas with alcohol into the tank just before you go flying. That should clear any water.

John.

 

[N8DAV8R]

IS or ULS? If ULS, Have you read the section in the FTS with guidance on this subject?



For Rotax 912ULS equipped aircraft complete the rest of the pre-flight inspection with the fuel pump running; about 2 minute, and then resample the fuel.

Since the 912ULS gascolator is not at the absolute bottom of the fuel system, running the fuel pump will help move any water trapped in other areas of the system into the gascolator bowl. If a sample yields a large amount of water, the procedure should be repeated with at least 2 min intervals between attempts with the fuel pump on, until all water or debris are removed from the system. The restrictor fitting on the return line limits the flow rate and the pause between samples allows time for fuel within the system to move into the gascolator.
The recommended fuel pump run time to flush the fuel system is based on the low flow rate through the return line restrictor fitting. Particular attention should be given to the battery voltage when flushing the system; turn off all unnecessary electrical equipment to conserve battery power. If the battery voltage is low, proceed to engine start and then let the engine run for at least 5 mins at 2000 rpm to flush the fuel system

 

[mmahony1]

Nate,

It's a ULS. Thanks for posting that snippet - I've only been referring to the POH and wasn't aware of the FTS. I haven't followed those instructions to the letter but have at points done substantially the same thing. I'll give it a shot today and see if anything changes.

What I think I've noticed is that the velocity of fuel flow seems to have a substantial impact on whether or not water is pulled from the system. The fuel pump can run for a couple of minutes without accumulation but if I sample for a while I do get water. This is especially true if I press the sampling port in a way that allows fuel to jet out quickly.

The thing that gets me though is that I can remove literal gallons of fuel and still get some water with it. Yesterday I removed three gallons and still had small amounts of water when I sumped.

John, thanks yes this thought has occurred to us. We were unsure what ratio of water to fuel would inhibit combustion which is why we have not attempted. We may do this and just drain the fuel rather than fly so we can have a clean slate of confirming the water ingress issue has been fixed.

 

[Piper J3]

If the battery voltage is low, proceed to engine start and then let the engine run for at least 5 mins at 2000 rpm to flush the fuel system

You might not want to do this if you have an early 912ULS without the new spark retard ignition modules. My RV-12 is SN120058 and has the green-label ignition modules with fixed timing in the advanced position.

When starting the engine with full advance, it is important that the battery be fully charged for fast (high-torque) cranking in case the engine would backfire. The hollow carbon fiber prop does not have much mass so a backfire can stop the cranking motion, or worse yet, reverse it. In either case… the Sprag Roller Clutch on the starter motor can easily be damaged and then you’d be having a bad day…

I keep my battery connected to an Odyssey charger that is designed for 24/7 battery maintaining. Engine cranks like there’s no tomorrow…

 

[Tony_T]

You might not want to do this if you have an early 912ULS without the new spark retard ignition modules. My RV-12 is SN120058 and has the green-label ignition modules with fixed timing in the advanced position.

When starting the engine with full advance, it is important that the battery be fully charged for fast (high-torque) cranking in case the engine would backfire. The hollow carbon fiber prop does not have much mass so a backfire can stop the cranking motion, or worse yet, reverse it. In either case… the Sprag Roller Clutch on the starter motor can easily be damaged and then you’d be having a bad day…

I keep my battery connected to an Odyssey charger that is designed for 24/7 battery maintaining. Engine cranks like there’s no tomorrow…

Jim, to say the green-label modules have fixed timing in the advanced position is not entirely correct or maybe I should say is an oversimplification of how the original modules work compared to the new "soft start" modules. This is not the thread for that discussion so I am starting a new thread "Soft Start Explained".