Thorp Air Command - T18.net

Not sure if you want to "hang" the valve off the tank. I know there are a few that put an extension on the valve so they can shut off the fuel while "seated." I also saw a T-18 that had a tank mount value that was NEVER used as you could not reach it and the valve was frozen from lack of use...so whats the purpose of the valve ? Not sure how many of us can reach that valve in flight in the seated position to shut off the fuel, if needed.

I want to be able to shut off the fuel for any reason. On the ground, in flight or in the hangar. After my flooding carb issues, I now shut off my fuel for RON's and when in my home hangar.

Hanging the valve off the tank does make the system a little more "KISS", but you may be able to make the fuel shut off system work a little better by upgrading the FSOV. I used the ANDAIR valve and have been very happy with it. Just my opinion.

RB

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Many installations attach the valve to the fitting coming out of the bottom of the tank. They use an extender from the valve to the knob so it can reached in flight. Reaching the shut off in flight is very important. I had a carb come apart inflight a month or so ago and the ability to quickly shut off the fuel quickly saved my bacon. This was on a seaplane (Maule) and I landed on a lake nearby. It will cost a beer to hear the whole story.

Another design feature that needs to be addressed is the routing of the fuel line from the tank to the gascolator. It must run downhill all the way while in the ground position or you can trap water in the line and not find it until the engine is drawing sufficient fuel to move it along. Those who have properly preflighted a modern Cessna 172 will know how hard you have to work to ensure all the water is drained out of a poorly designed system.

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Bob Highley
N711SH
SN 835
KLAL

On the subject of hanging the shut off valve off the tank:
I read a comment in an old newsletter (#60 something) the other day challenging the idea that a valve hanging from the tank will ultimately result in cracking at the boss in the tank. I was also interested to see that a high percentage of the Thorps that I have looked at recently had valves hanging from the tank and they seem to be doing quite well. So, what do the owners of high-time T18s say about it now? Was the cracking problem exaggerated, perhaps, or are we seeing problems in this area?

MLM had the valve plumbed directly to the tank, and it sure made for a simple installation.

DW

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In theory, theory and practice are the same. In practice, they are not.

I think it may be a combination of several factors...

1. How and who made/welded the tank/boss. I bought my tank from CSA and even though I pressure tested it (it checked OK), I put Pro Seal on all the external seams.
2. What type of valve was installed "under the tank."
3. If the valve "under the tank" had some sort of extension to make it easier to operate from the seated position, putting "stress" on the boss.

I know of one under the tank valve that was "frozen" in the on position because it was never exercised from the on to off position. I can see why as I would no want to crawl under there to turn it on and off ! If you have a valve under the tank that is used on a regular basis (extension or not) I don't really see a "stress" issue...depending on the type of install.

Case in point try turning off that under the sink or toilet shut off valve ! 90% of the time it won't turn or leaks when you try to turn it off ! [:0]

RB

A couple of things ..

One, the old brass weatherhead valves can get very hard to actuate. When mounted on the tank flange they can induce cracks when operated over time. The newer valves have a nylon ball that has a much smoother motion, I suspect you're "ok" using those on the tank flange.

Two, don't forget that the regs state (and for safety sake) that you need to be able to reach the valve or in some way be able to shut the fuel off in flight. Keep that in mind when contemplating shut off valve locations. I'd feel best having the valve mounted on something solid and a push pull or pushrod to actuate it.

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

Hi Dick, I used a Stainless ball valve under my tank, it is 1000psi oil gas or water valve. I welded a AN bushing right to the bottom of the tank as the bushing has quite a shoulder on the hex end of it. I fashioned a 3.5" dia disc that sat down around the bushing and conformed to the shape of the tank, this disc was made from 6061-T6.125 thk, I welded the disc to the bushing and the intire OD of the disc to the tank.This made for a very rigid valve mount, the valve is a.375 valve by the way. If the tank is built to spec it is built from 5052 alum and this is softer than 6061, but it is more malable, it shapes,and bends easier without fracture.5052 is also less apt to corrode as it is a marine grade alloy, so it is good stuff for a fuel tank. I have shut off my fuel probably 3 times in 3 years, but if I had to do another tank I would do it the same way just as an insurance policy. Dont know if I helped you or not, but this is just one way of getting it done and having the bottom of the tank reinforced a bit for the valve to be directly mounted...Dan

Dan the welding man ! I think you need to put on a welding clinic at the next KVIS Fly-In ! After my carb fuel leaking problem, I shut my fuel off when ever the A/C is parked overnite(Ron) or in my home hanger. Andair fuel valve..."Priceless !" The fuel valve is part of my before start and before T/O check list. Don't leave home with out it ! [:D]

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RB

The Andair Valve, always heard good about that valve, never anything bad. Shutting off the fuel is probably always a good Idea, I should do the same, I afixed my shutoff so when the fuel is off it pokes me in the leg, most anoying but a good reminder. Its the little polished lever on the console below the mix knob. It is attatched to a piece of 1/2" 2024T3 tube that actuates the ball valve,the handle that comes on the ball valve can be modified to recieve the tube and a 3/8" socket universal to streighten things out......I will practic shutting off my fuel and see if I can depart from my laziness a bit....Dan

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For some reason I thought you had the Andair valve ? Your set up is as clean as the rest of your A/C ! Very professionally done !

RB