PDF | FULL TEXT

You will need Adobe Acrobat to view this document.
Get a copy here

From the Wiregrass Radio Control Club, Enterprise, Alabama

Refuel Fill Valves

by Jim Kale

I have noticed many having problems with refuel fill valves for the last couple of years. It is just my opinion; however, many of the refuel valves that require a special plug to be inserted into a special jack just don’t work too well in the long run. Valves such as the DuBro quick fill often seem to work well in the beginning, but in a year or two, they become difficult to connect, possibly leak, can easily get dirt and debris into your fuel system when you connect the refill fittings, etc. When they have a problem like this, they often cause lots of difficulty, frustration, and bad language at the flying field.

Recently, Phil was trying to fly one of his big gasser models that was having engine run problems for more than two years. Phil had picked up the model at Perry, and it looked to be in great condition; however, there is no way to know how long it had been hanging in a workshop somewhere. After lots of frustration, bad language, and trouble shooting, we finally traced the problem to the refuel fill valve. It was letting air get into the fuel line and the engine would not run reliably. When the refuel fill valve was removed and replaced with a short brass tube, all of the problems went away and the engine ran like a new one. Unfortunately, on the next flight, the airplane stalled and spun in, possibly because of radio problems. Phil said it was really great though to have the engine perform well—for at least one flight.

I am a firm believer that the best way to refuel is a dedicated third fuel tube that goes straight to the tank. It should have a plug to close it off after refueling is complete. That means you have three lines coming from the tank: one for the vent, one for the feed line to the engine with a clunk inside the tank and a filter as close to the engine as is practical; and one is the refuel line with a plug in it when it is not used for refueling. A fuel dot is the ideal way to keep this line easy to get to for refueling the model. This is about as simple and fool-proof as you can get. You could use a T-fitting in the fuel between the filter and the tank, and put a line on the end of the T and keep it capped off except to refuel. However the problem with this arrangement is that often when you pump fuel into the line, some of it will go out the carb and onto the ground.

Always use a filter as close to the engine as you can put it. If you use a filter on the clunk inside the tank and then refuel through this line, you will pump debris into the filter from the engine side and it will quickly go back up the line to the carb as soon as you start the engine. We have all seen pilots who spend the bulk of their day at the field having engine run problems because they failed to take these simple precautions when they installed the fuel system. Don’t make your flying life miserable and difficult when it is easy to do it correctly the first time.

By the way, when you cut brass tubing to be used in the fuel system, file the ends of it smooth so they are not sharp and cut into the line making a very hard-to-find air leak. A little good building practice will make life much more fun on the flying field. We all want to fly when we go to the field, not spend all of our time troubleshooting problems that we inadvertently caused by poor construction.

If your model survives several years, you should remove the fuel tank system every couple of years or so to make sure you don’t have any problems developing. Alex Perez recently brought his 12-year-old model to the field and found that the engine would not run correctly. Then Alex remembered he had not checked the tank system since it was new. He did the correct thing and went home and restored the fuel system to a serviceable condition and it ran great the next time he came out.

It is very easy to forget how old a model is if it has been performing well for several years. I once flew a model for six years without fuel difficulties. When the next flying season rolled around, somehow I thought about checking the fuel system. The fuel filter has so much crap in it that I doubt the engine would have run at all. So, I probably saved lots of possible frustration and agony at the field trying to get it started and running. Q

Home       Archives       About       Contact      AMA       Publications       Subscribe       Unsubscribe