I disagree
A gascolator will catch water that passes through mixed within the fuel flow, as long as the flow rate is not too high.
This is of value since sumping tanks doesn’t necessarily drain all water from fuel tanks (water can be trapped in areas that prevent it from being drained but in flight, can make its way out of the tank.
Testing I have been involved with showed that water in a high pressure, high flow volume fuel system tends to not have any negative effect on engine operation.
At least that was the case with the test we did on the Rotax 912iS when a shockingly large amount of water was purposely induced into the fuel system.
Scott
If the during flight the purpose of the gascolator is to strip water from the fuel, then in high flow / high pressure applications, as you admit, it is not up to the task.
The only way water will collect in a gascolator is if the flow is so low that water can settle out; also as you note. My testing shows this will not happen in EFI systems. The capacity of most gascolators is quite small so theoretically it would only be possible to remove a small amount of water during flight.
I would be interested in knowing how low the flow rate & pressure would need to be to allow water to settle in the gascolator. I have yet to see any technical data on this. If there is any technical data on gascolators, it would specify when this device would be of value.
If the tanks are sumped PRIOR to flight, any significant water contamination would be removed. IMHO the best solution is to eliminate water before it enters fuel lines rather than attempt to remove unsafe amounts after flight has started. In other words, an ounce of prevention......
In EFI installations, If any of the gascolator seals (O-rings) leak, air will be introduced on the suction side or fuel sprayed under pressure on the pressure side. Either situation could be catastrophic. Why install a device where it is ineffective and presents a risk?
In the RV10, I was able to introduce 500 ml of water into a fuel tank and remove all but a few mils using the drain. The remaining water, somewhere in the tank - behind ribs etc , was demonstrated to have no effect on engine operation. This mirrors your Rotax experience.
Further, in an installation that uses a closed loop fuel system and electric fuel pumps, any water in the fuel lines or gascolator would be swept back to the fuel tank within a couple of seconds of bringing the fuel pumps online before engine start. This water would be mixed with fuel in a concentration trivial with regard to engine operation.
A couple of final points, the TCCA regulation governing amateur built aircraft requires: "a gascolator located at the lowest point in the fuel system". This means it must be installed below the fuel tanks. Words matter where regulations are involved - clearly this one was very poorly written. Recreational Aviation Services Inc who control Canadian inspectors cited my last RV10 inspection for "Fuel system has no way to sample fuel for water" as I did not have a gascolator or drains on my inline filters. Clearly their concern was pre-flight testing for water not stripping water from flowing fuel.
