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Has anyone ran into any problems concerning low fuel quantity, with regards to cold weather operations and closing the oil cooler air inlet? I am flying a B2-B sn 470. I would like to see if anyone else out there has the same problems...............Mike

My problem is that when I have the oil cooler door anything but all the way open the fuel quantity works fine, but if I close it partially, the light stays on, due to not enough pressure on the switch..............

JetStar:
You probably know this but the ONLY thing that affects QUANTITY of fuel left whe the light comes on is the ELEVATION of the 'TEE"
above the bottom surface of the lowest point in the lower fuel bladder. ( the "tee" I'm speaking about is under the pilot's seat aginst thefirewall.)

If you, say for example, put 3 gallons in a totally empty tank before the fuel level raches the tee, then the light will come on AT THE 3 GALLON LEVEL. You can ONLY change that setting by bending the fuel lines under the pilot' seat to change the HEIGHT of that tee. During maneuvering, as fuel quantity gets low, the fuel sloshes and intermittently covers/uncovers the tee. This makes the low fuel warning light blink.

As fuel level gets even lower, there's a point where even while maneuvering, the sloshing fuel NEVER covers the tee. At the this point the light comeson solid.

Now to the Dwyer pressre switch. If this switch is CLOSED, the low fuel warning system is ARMED. If the Dwyer pressur switch is open, the low fuel warning system is NOT armed.

In your scenario, there is only 1 setting of the oil cooler door that properly ARMS the warning system. Your problem could be:
1)Dwyer switch has the setting screw too tight on the spring that sets how much engine compartment positive pressure it taks to close the switch.
2)Defctive or leaking Dwyer switch
3)Hose supplying positive engine compartment pressure to the Dwyer switch is not sticking into the oil cooler compartment like it's suppose to.
The maintenance manual goes into some adjustment procedure of the Dwyer switch using a coke bottle & water. That's crazy. Just
low-hover with an extremely low (AVOID RUNNING OUT!) fuel level, set your oil cooler door where the light will NOT come on, then land and slightly loosen the Dwyer adjusting screw (by the voltage regulator) , then hover again. Repeat until you have the screw adjusted
correctly so the Low Fuel Warning System arms no matter where the oil cooler door is set.

Then you can raise or lower the "tee" under the pilot's seat as you wish to adjust fuel QUANTITY you want remaining when the light comes on.

I hope this helps.
Bryan

Bryan, thanks for the reply. I understand how the system works, but it just seems that this was a poorly engineered system. In that if the oil cooler door is closed, the system will never arm and you have an idiot light on at all times. It would seem that my switch might need adjusted............................thanks again..............Mike

Mike:

My guess is that you can adjust that screw so that even with the oil cooler door all the way closed, the Dwyer switch will arm.

Mine worked if the door was completely closed.

Bryan

The way I read the manual the switch is normally closed until you get up to about 2200 rpm or so and the ram air pressure the switch sees then OPENS the switch and the light goes out. When the fuel goes below the level of the fuel tee it then vents the ram air from the switch overboard thru another static port and the switch closes and the light comes on.

What you are calling RAM AIR PRESSURE is actually positive pressure created in the engine bay by the 2 cooling fans. (on the B-2B)
If you have the set-point on the Dwyer switcch adjusted wrong, and if your oil cooler door is closed, the pressure won't trip the switch because the oil cooler door blocks off the area where the air tube to the Dwyer switch is.

Well it looks for all the world like a miniature Pitot tube positioned to catch the air behind the door-on mine it actually is positioned straight forward just behind the door. Coupled that with the fact that there actually is a third static button that bleeds the air off the switch(when the fuel tee is unblocked with fuel) makes it easy to visualize how the thing works. Somebody had their thinking cap on to come up with this system lol.