NTSB Safety Alert - Fuel Selector Valves

How to keep the Cessna 170 flying and airworthy.

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GAHorn
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NTSB Safety Alert - Fuel Selector Valves

Post by GAHorn »

The NTSB has issued a safety alert on Fuel Selector Valves which brings to mind several calls I’ve rec’d recently from Members who have the older, brass selector valves PN 0511122 or PN:0413020-3 (essentially identical valves, primarily in 170 and 170A models) which were originally mfr’d by Weatherhead or Kohler (sometimes referred to as “Cessna-crafted” valves.)
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These valves have a brass “cone” within the main body with the “cone” being machined with a “T” -shaped passageway that allows fuel to be selected from either or both tanks… or “OFF” may be selected … with the caveat that fuel can still exchange between the wing tanks since the “cross-over” passageway still connects the two tanks. (Later 170B aircraft are equipped with a completely different valve. That valve PN 0513120-5 has its’ own special issues which I wrote about in the First Qtr 2011 “170 News”: https://cessna170.org/download/24/170-n ... r-2011.pdf )

With the early valves, the problem is owners often wait until their valves become leaky or stiff and difficult before they address any maintenance for them and by that point they often are damaged beyond repair. The brass “cone/body-interface”, once dry of lubricant, become stiff …and if an owner continues to force it then the valve becomes scored/damaged possibly beyond repair. It’s my personal belief that valves which are frequently operated survive longer because the lubricant continues to be spread within the valve…. that valves are like many other things in life… “use it or lose it”. I recommend that airplanes left alone between flights should have their fuel valves selected to “Off” and that the valves be excersized occasionally thru all positions. I believe most owners do not do that however, …that they leave it in the “Both” position for months if not years on-end. The only time those valves are excersized is once-per-year during annual-inspection when the gascolator screen is cleaned. (I think the valves should be maintained “preventably” by occasional disassembly/lubrication/new-o-rings. And if your valve is already stiff and getting stiffer….STOP OPERATING IT before you kill it completely… have it disassembled, cleaned, lubricated and resealed.)

Most owners are probably intimidated by their valves…frozen by fear…until their valves are frozen also…and then, by forcing them to move…. wipe them out completely. Then they discover the early “brass’ valve is virtually unobtainable but Textron/Cessna has a newer-design replacement valve priced alongside the items they supply to the planned NASA Mars Mission.

McFarlane advertises that they will repair/rebuild the older valves at “price to be determined”…but often by the time they’re submitted they’re in too bad shape to be saved.. My previous A&P/IA would rebuild them but retired, and now retired and Gone West. He used ordinary nitrile O-rings and “Fuel Lube”.

Without naming-names…. modern versions of those valves are still made and sold thru marine distributors…. even on Amazon (where I bought one for my boat. Aircraft Spruce also sells them for experimentals)… un-named persons I know have used these on their airplanes, cross-drilling them to accomodate a “both” position. The 3-way 1/4” outlet version is identical to the older aviation version in 170s….except that the old brass “cone” is a delrin-type of plastic just like the versions Piper used in their early airplanes….. and also except that the cone is not drilled in a “T”…but in an “L”…. such that fuel can only be drawn from one tank at a time. It’s a shame that the “cone” isn’t drilled completely “thru” to make it into a “T” …because if it were..it’d be a near perfect replacment for our early 170/170A fuel valves….

The shaft of these new marine valves is longer but shouldn’t be a problem except for looks. I guess if a guy was really picky….it could be cut shorter and the selector/pointer/handle then refitted….. all for the “experimentals”, of course…

Here’s the NTSB alert: (Notice the picture of the disassembled Piper valve with the plastic cone that is cross-drilled). https://piperowner.org/wp-content/uploa ... SA_075.pdf

https://www.amazon.com/Moeller-Three-Wa ... 043&sr=8-4


From an NTSB Accident Investigation: “ Review of the airplane maintenance manual revealed instructions, applicable to 100-hour inspections, for the fuel selector to be inspected for condition, security, and operation. According to the instructions, if the fuel selector valve binds, sticks, or is otherwise difficult to operate, the fuel selector valve should be lubricated. Specifically, the insert, position washer, and "O" rings should be lubricated.

“ Probable Cause and Findings
The failure of the fuel selector valve in a position that restricted fuel flow to the engine, resulting in a total loss of engine power during initial climb due to fuel starvation. Also causal was the operator's failure to effectively detect and resolve the wear and progressive binding of the fuel selector valve before it failed due to excessive rotational force being applied. Contributing was the flight instructor's exceedance of the airplane's critical angle of attack during an emergency return to the airport, which resulted in an aerodynamic stall/spin.”

https://www.aircraftspruce.com/pages/ep ... /whfsv.php
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'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
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dstates
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Re: NTSB Safety Alert - Fuel Selector Valves

Post by dstates »

Good info, George. One additional thing to note is that some of the brass 170 & 170A valves have graphite packing in the top nut instead of o-rings. Mine was this way. My A&P and I found a suitable graphite packing for replacement but it took a few tries getting the right length of it installed to make a good seal and not be too tight to install the cap.

I believe the previous owners of my plane did not use the fuel valve and when I started using it occasionally (it was stiff) it started leaking after about a year of ownership.

When you have it disassembled, go ahead and lap the brass cone with the valve body.

Also, it is in a difficult location to remove/replace. Not impossible, but difficult. I did fabricate a short aluminum plate with two nut plates on it to make installation easier. I would highly recommend anyone else working on this valve to do the same.

I read in another post here once that working on a leaking fuel valve and broken door latch springs are a right of passage for all 170 owners. I can proudly say I’ve done both. :wink:

Doug
N1235D - 1951 170A - SN: 20118
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cessna170bdriver
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Re: NTSB Safety Alert - Fuel Selector Valves

Post by cessna170bdriver »

I exercise my fuel selector every time I top off with fuel by turning it to one tank or the other during fueling. My OCD tells me to do that to prevent crossfeed from the full tank to the less full tank. I doubt it really makes that much difference, but it does exercise the valve. Also, lately I’ve been trying to get into the habit of turning the selector off any time I pull the prop through.
Miles

“I envy no man that knows more than myself, but pity them that know less.”
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dstates
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Re: NTSB Safety Alert - Fuel Selector Valves

Post by dstates »

cessna170bdriver wrote:I exercise my fuel selector every time I top off with fuel by turning it to one tank or the other during fueling. My OCD tells me to do that to prevent crossfeed from the full tank to the less full tank. I doubt it really makes that much difference, but it does exercise the valve. Also, lately I’ve been trying to get into the habit of turning the selector off any time I pull the prop through.
I do the same thing when fueling…
N1235D - 1951 170A - SN: 20118
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