Cessna killer caps, or not?
Join Date: Jan 2002
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I was going to mention the rubber bladder things but got beaten to it!
As far as separation is concerned however I can add something. In oil and gas processing the rule of thumb to separate oil from water is a residence time of 2 to 3 minutes. Given that we are talking about petrol and water (so less vicous and less dense than crude oil) the separation time will be less than a minute. So as soon as you have put the filling hose away you can use the drain cocks.
A bigger issue than time, is however getting the water to the drain cocks. With wide flat tanks using a natural slope is the obvious solution - but it does mean the aircraft has to be turned around.
As far as separation is concerned however I can add something. In oil and gas processing the rule of thumb to separate oil from water is a residence time of 2 to 3 minutes. Given that we are talking about petrol and water (so less vicous and less dense than crude oil) the separation time will be less than a minute. So as soon as you have put the filling hose away you can use the drain cocks.
A bigger issue than time, is however getting the water to the drain cocks. With wide flat tanks using a natural slope is the obvious solution - but it does mean the aircraft has to be turned around.
Join Date: Feb 2008
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More information on the alleged "killer caps." Also used on Cessna 310, several Beechcraft models, and later Grummans.
CSOBeech - Beechcraft Fuel Caps
CSOBeech - Beechcraft Fuel Caps
Join Date: Jul 2009
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I would like to commend the points made by Pilot DAR and Sigurd in their prior postings. These are the key issues with water in the fuel that I've experienced while owning two Cessna 210s (1960 and 1970 models).
That small o-ring surrounding the connecting 'bolt' below the flip-up lever has got to be a big part of the problem. Since it is not visible just looking at the cap, it is easily missed.
My second 210 showed me that water in the fuel can be a particular hazard when it gets well below freezing. I had left the fuel valve open intending to help the water get to the low point, for easy sumping. What happened instead is that the electric fuel boost pump was damaged from ice expansion and I lost one tank of fuel!
Fuel systems really are not intended to hold significant water. Boost pump replacement is expensive. Fuel is expensive. Do not let the water get into the system in the first place. Buy the upgrade caps!
That small o-ring surrounding the connecting 'bolt' below the flip-up lever has got to be a big part of the problem. Since it is not visible just looking at the cap, it is easily missed.
My second 210 showed me that water in the fuel can be a particular hazard when it gets well below freezing. I had left the fuel valve open intending to help the water get to the low point, for easy sumping. What happened instead is that the electric fuel boost pump was damaged from ice expansion and I lost one tank of fuel!
Fuel systems really are not intended to hold significant water. Boost pump replacement is expensive. Fuel is expensive. Do not let the water get into the system in the first place. Buy the upgrade caps!
