Sky Sports offers their senders in many sizes, and will custom build pretty much to any length. They even make ones with a bendable portion. Since the RV tank senders are designed to insert from the side of the tank, we need ours bendable to get the probe portion to span from the top of the tank to the bottom. In order to get the most accuracy possible we plan to have the probe portion of the sender run diagonally from the lowest point in the tank next to the fuel drain, up and outboard across two bays of the fuel tank. In order to get the probe portion down to the lowest point, the first 7 inches of our sender is bendable. Before bending the senders I plan to make a mockup from a bent clothes hanger. I also put some marks on it... the one at the far left marks the bendable portion of the sender (everything to the right of the line is bendable). The next line over is the closest I can start a bend to the head of the sender (this is due to our bender not physically being able to get closer to the head of the sender), and the last line just marks the end of the aluminum portion of the tube.
Here is my first pass at bending the mockup. This shows the general idea of what we're shooting for. One important point here… the tube of the sender can't touch any metal inside the tank.
Here… this is what I'd like to do… However, without getting too wordy, I'm not sure if I can have the sender start at the bottom and go up (as opposed to starting at the top of the tank and going down), so I tried calling Sky Sports. No answer so I sent them an email... So, I'll move on to something else for now.
Turning the "empty" screw I adjusted the voltage to 0 volts.
Now to see if they'll actually read a different voltage when fuel is
introduced I capped the end of a small PVC pipe and filled it with auto
gas (I'm only doing this now for testing… these guys will be
re-calibrated on the plane later) Once it was secured to the table I
submerged the sender... the deeper it went, the greater the voltage
read... yea... it works! Once it was fully submerged I went ahead and
adjusted the full screw until the multimeter read 5 volts... again
probably not necessary, but hey, I get the feeling of doing something
electronically important (a challenge for me!)
Since I had everything set up, I went ahead and tested the other sender in the same manner.
Now for the moment of truth… bending the thing to fit in the tank… This turned out to be quite frustrating. Once I got over being nervous about trashing the thing, it became nothing but a trial & error event. The shape that provides the best position for accurate reading doesn't necessarily coincide with a shape that can be installed. I used my clothes hanger as a guide, and that's pretty much all it is... Once it was more or less at it's overall shape, the clothes hanger pretty much is worthless... but there's still a lot more fine tuning to do to the sender. I wanted to get it relatively close to some other items in the tank so I can dab some proseal between it and some structure to keep it from bouncing around... but at the same time it can't touch anything in the tank... like I said, trial & error. Anyway, to get to the final shape I found I had to shorten the sender (3 times) a total of about 5 inches.
Once I finally got the fit acceptable, the final thing to do was to drill this hole at the appex of the bend at the lowest point. If we don't put this in, the lowest opening the fuel will have to drain out of the tube is at the head of the sender unit and that's mid-way up the tank.
Not wanting to go through the effort tonight, I'll need to test this thing one more time to make sure it still works after the bending and cutting... next time...
Now for the moment of truth… bending the thing to fit in the tank… This turned out to be quite frustrating. Once I got over being nervous about trashing the thing, it became nothing but a trial & error event. The shape that provides the best position for accurate reading doesn't necessarily coincide with a shape that can be installed. I used my clothes hanger as a guide, and that's pretty much all it is... Once it was more or less at it's overall shape, the clothes hanger pretty much is worthless... but there's still a lot more fine tuning to do to the sender. I wanted to get it relatively close to some other items in the tank so I can dab some proseal between it and some structure to keep it from bouncing around... but at the same time it can't touch anything in the tank... like I said, trial & error. Anyway, to get to the final shape I found I had to shorten the sender (3 times) a total of about 5 inches.
Once I finally got the fit acceptable, the final thing to do was to drill this hole at the appex of the bend at the lowest point. If we don't put this in, the lowest opening the fuel will have to drain out of the tube is at the head of the sender unit and that's mid-way up the tank.
Not wanting to go through the effort tonight, I'll need to test this thing one more time to make sure it still works after the bending and cutting... next time...
I also slathered a bit of proseal between the probe and rib where it
passes through the hole, and finally between the probe and the vent
line (making sure not to plug the end of the probe). This should
ensure it isn't capable of bouncing around and touching anything. In
order to get it in exactly the spot I wanted I used this 2x4 to put a
slight bit of pressure on it while the proseal cured.
Here's a pic showing the sender probe right side up. So, the bend is
the low point… this is why we needed the small hole drilled there.
Notice also that the proseal insulating the probe from the stiffener at
this point is sort of off to the side… this is so it wouldn't plug up
that small hole. Also in this pic you can see the flange for the fuel
pickup at the bottom right. So, the fuel sender should almost read
down to completely empty.
Here's a shot of the exterior of the inboard rib of the left tank showing the arrangement of the fuel sender
& AE Fuel Guardian.
