Not too long ago I switched to the Jersey Modeler Pump system with 7.2 Volt battery after using a hand pump for years. Yesterday, I luckily noticed that my fuel system was not de-fueling correctly, and found out that my Sullivan header tank on my Kingcat had developed a small crack at the rear corner from the constant flexing of the tank when fueling/defueling. This could have cost me a flameout (and the airplane)-Do I remove a battery and run the pump on lower voltage or go back to the hand pump ? Opinions welcome. Thanks-Mike Oberst

Mike,

I had the same problem on my Kingcat, when I de-fueled, the Jersey modeler would collapse my center tank, causing it finally to leak and I had a flame out. This also happened to a fellow modeler here in MN. I talked to Dave at BVM and he said they just don't empty the tanks unless they are going to store the Jet for a long period of time.

What I did was install a more rigid center tank, similar to the UAT, just larger. This helped the problem, but now I just leave the fuel in the plane.

I also had the problem of the tank filling to quickly and swelling the tanks in my F-15, so I removed one cell from the JM.

Hope this helps,

Kevin

Hi Mike,

Are you filling into the header tank and is the brass tubing going from the header to the main tank small? If it is, try installing a larger tube. I found that the main tank on my Boomerang would swell when the piggyback tank I put on top of it was fliing because of the restrictive small tube connecting them. You could also try running it on a 6V pack.

Bob

If your fuel tank is expanding/contracting during fueling/defueling it's because your vent is too restrictive for what your pump system is delivering. There are several things you can do to prevent or minimize this:
- Go with larger diameter tubes and lines on your tank vent and between tanks.
- Put a restrictor in line on your pump system or go with smaller diameter lines to reduce its flow.
- Reduce the voltage on your pump system.

Since I have one main tank plus a UAT I fill directly into the main tank.

Joe

Mike:

On my KC, I had the same problem with the Sullivan 16oz Boat tank that BVM ships with the kit........my solution was to switch to a Sullivan 16oz Round(cylindrical) tank........this contour resists deforming.........zero problems with my Jersey at 7.2 volts since the change.....I can actually run 12 volts across the pump and the center tank doesn't swell significantly, either filling or emptying........it just fits between the 2 main tanks when pushed all the way back against the aft bulkhead.......

I have had similar bloating problems with other tanks in series/parallel on my Avonds F-15, AD F-16, SJ F-16, all solved by going to the round tank setup.........I still get a little bloating in my UAT......

Actually, a little bloating is not all that bad since it allows one to check for leaks before heading out on a sortie......


Tom

Our first home made fueler used the same pump and we ran it right from a 12 V gel cel...no problems at all until we tryi to fill the taxi tank in series with the main tank...then we have to pulse the pump for 20 or 30 seconds and wait for the bulging main tank to subside..... This would kinda support the small vent theory...
However, we did put an automotive fuel filter on the output line of the pump, so this would reduce the flow somewhat....

I'm glad I have one of those overpriced UATs though..I never considered the fuel pressure going through these things...

our new pumps run on 7.2 volts.

Hi All,
After reading this thread I did some looking at the King Cat and the Composite Bob Cat fuel system. The inside diameter of the UAT nipple where the fuel is pumped in is .103 inches as is the inside diameter of the UAT nipple going to the Sullivan header tank. The brass tubing, as supplied by BVM, for the Sullivan header tank has an inside diameter of .125 inches for both the inlet and outlet. Now comes the problem - the outlet of the Sullivan tank routes to a Tee fitting, which goes to both main tanks. The inside diameter of this BVM white plastic Tee fitting is .083 inches - big problem!! The main kevlar tanks, which have the threaded in aluminum fittings, have an inside diameter of .092 inches - no problem since there are two of these fittings. So what we have here is a restrictor right in the middle of the fuel system. If you calculate the cross sectional areas of the parts you will see that the Tee fitting has 35% less area than the UAT input fitting. So during fueling once the UAT and Sullivan header tanks are full unless the flow rate from the caddy is REALLY LOW you will build up pressure in the UAT and Sullivan tanks. During defueling if any fuel is in the two main tanks you will cause the UAT and Sullivan tank to suck in until there is no more fuel in the mains. In order to alleviate this pressure problem it is mantatory that all lines and fittings downstream of th UAT input nipple have an inside diameter at least equal to the inside of the UAT input nipple. This ignores the pressure you will get just pushing the fuel through the system, which should not be high enough to deform the UAT or Sullivan header tank. The BVM Tee fitting needs to be replaced with one which has an inside diatmeter at least as big as the UAT input nipple. The same white Tee fitting is used in the vent system from the main tanks, so if you use an overflow tank, as we all do, you must change that fitting also.

I was just ready to do the final installation of the tanks in my composite Bob Cat, so that is where I measured these parts. I will use bigger Tee fittings in that airplane. My King Cat is a couple of years old and has the BVM white Tees. I have not noticed flexing during fueling/defueling, but I have not paid much attention either. I do notice that during a full power run-up that the UAT sucks in a little!! I will change the Tees on the King Cat before it flies again. It is raining and blowing so hard here in the Northwest I need something to fill in the time anyway.

Al Watson

Thanks to everybody that replied.
Al-I would be interested to know which Tee's you end up using, and where you get them, as I might give this idea a try. It sounds logical to me.
Thanks again-Mike O

Excellent analysis, Al. I spent the last 5 years designing car and truck fuel and evaporative emission systems for Ford Motor Co. The most common cause of automotive fueling problems is vent restriction.

Mike,
Most auto parts stores carry a variety of tees.

Joe

I use the large black T's you see in the sprinkler section of the hardware store, very large ID