lml@lancaironline.net Mailing List Archive

Hi Craig,

Just a few last comments on this thread.

By your description of your filter, you have what I believe it would be best called a filter bypass feature rather than a pressure relief valve. I think we both agree why this is necessary. If you were to plug the filter with contaminants it would be best to keep the engine running to return to the airport. Even at the expense of putting contaminants in the whole system.

The other reg that I did not display talks about quantity. It uses terms like "sediment bowl" which would indicate that be at has the capacity of trapping a "volume" of contaminants. The bypass filter that you have is not designed to trap and hold any contaminants.When the quantity of contaminates cover the surface of the filter to the degree that the pressure differential overcomes spring pressure-- it bypasses.

The reg 23.971 talks about a quantity that the sediment bowl (gascolator) is able to hold. Is that important? I think so.

I mentioned that I had seen water and even mud in gascolator's in my years of flying experience. These cases were mostly all around ferry flights where airplanes had been stored for long periods due to death/incapacitation of the owner etc. etc.. Some of these airplanes were stored outside for a while. After shaking the wings-- draining the sumps until clear, I still was thankful for a sediment bowl to trap the remaining contaminated contents.

Your comment about observing "43 gal per hour to 42" and noting that change as a indicator that the filter is becoming plugged, is not practical in my opinion.. Variations in altitude, temperature, rpm and manifold pressure and indicators would make this impractical.

The engine-driven fuel pump will compensate (up to a point) for the partial plugging of a filter up stream-- and therefore mask that restriction.

You're right, that it is one of those "personal decisions", (isn't amateur building great!). However, "not so good left over's from a long time ago" is not true, in my judgement. And the noose is tightening with the requirement of insurance inspections, and one of the issues that they are extremely concerned about is "modifications" such as this.

Section 23.971: Fuel tank sump.

(c) Each reciprocating engine fuel system must have a sediment bowl or chamber that is accessible for drainage; has a capacity of 1 ounce for every 20 gallons of fuel tank capacity; and each fuel tank outlet is located so that, in the normal flight attitude, water will drain from all parts of the tank except the sump to the sediment bowl or chamber.

(d) Each sump, sediment bowl, and sediment chamber drain required by paragraphs (a), (b), and (c) of this section must comply with the drain provisions of §23.999

Charlie K.

Charlie, my fuel filter has an internal pressure relief to prevent a plugged filter from stopping fuel flow. I think this plugged fuel filter condition can be prevented through normal maintenance by monitoring take off fuel rate. If fuel rate drops from 43 gal per hr to 42 then checking the filter is in order. I will need to pull the top cowl, but cleaning the filter is a piece of cake after that. I also have the stock high pressure overboard relief.

I have had others say they have found stuff in a gascolator as well. I have been a "poor" flyer for 20 plus years flying 40 year old planes that set on the tarmac all day and night. I have seen water and particles in the tank drains many times, but NEVER in the gascolator.

The Bonanza has two perfectly good drains, one in each wing. Since it is a low wing, it must meet the requirements of FAR 23.999. I can't say for sure as I'm not up on all the far's, but it passes annuals.

I think the gascolator is one of those "personal" decisions, but in my opinion the design is one of those not so good left over's from a long time ago and the low volumes of general aviation won't pay for an upgrade. While our constant flow injectors are not nearly as sensitive as the automotive electronic injectors, I still believe a fuel filter is important and a necessity. That is the main point I wanted to make. Specifically, I feel a filter is a positive rather than a hindrance. The FAA obviously disagrees with me as well.

Craig Berland