Zenith Aircraft Builders and Flyers
Online Community of Zenith Builders and Flyers
Better seal for gas tank float sending units?
I was not happy with the instructions that came with the sending unit ring in that it gave a very small area to seal with, so I did something different:
I cut a slot in the ring so that it could be put through an opening the size of the inner hole of the rubber gasket.
Start one of the short screws to keep from dropping it, then use the long screw to get the float assembly started, then remove your helper screw.
This gives the whole gasket area room to seal, instead of just a tiny lip.
Replies to This Discussion
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Permalink Reply by Angel Galicia on
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the sender unit looks like a VDO do you know the impedance? (Ohms)
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Permalink Reply by Earnest Fontenot on
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Angel,
I bought the VDO sender units.
The ones I have run from 5 to 80 ohms.
Earnie
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Permalink Reply by Pat on
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Good job, The addition of locking split washers under the screw heads will retain the screw torque. Why washers aren't called for in the installation is a wonder.. Also a gas sealant on the threaded shank area of each screw. :) Pat
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Permalink Reply by John Bell on
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Did you bend the sender rod a full 125 degrees as in photo guide? When I do, i cant get the 8 to 80 ohm readings.
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At about 115 degrees bend I can get 10 ohm to 69 from a point 70mm from front/77mm from tank bottom. I think that will work but its not according to the guide.
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Permalink Reply by John Clark on
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John, what gauges are you using? I recommend this one from BeLight:
http://www.beliteaircraftstore.com/universal-led-fuel-gauge-with-2-...
You can calibrate it to whatever resistance you get.
Make the bend so you get full travel from bottom of tank to top of tank, and don't worry so much about the resistance reading.
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Permalink Reply by Guy Fortier on
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Our CH601 HD does the exact same thing! same problem on both tanks!! where can i get or what part # is the inner ring and it's gasket??
If you could help us out with this agonizing problem that would be awesome
Thanks
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Permalink Reply by Mike Chapman on
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That's a GREAT idea, John. Thanks for sharing. I agree with what others have indicated...that is one of the trickier things to do.
Mark Pensenstadler published a great YouTube video showing how he installed the fuel sending units on the top of his fuel tanks. I unashamedly copy many of Mark's ideas; so, I put my fuel sender on the top of the tank (Super Duty) and added an access panel so I can change the sender out more easily when it fails.
I'm ready to do the other sending unit...AND...your suggestion is how I will do my next fuel sender installation.
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what VDO Sending unit part # did you use? 221-012? 8 to 80 OHMS?
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Permalink Reply by John Austin on
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If the VDO sender you're installing has the white insulator in the center (as pictured in the first post of this thread) and you're mounting it in the side of the tank, I'd recommend dry-fitting it and ensuring you have full range of motion and good resistance readings, then install it with Pro-Seal instead of the rubber gasket and also, once the wire is attached to the contact on the white insulator, cover and seal the insulator with Pro-Seal, also. See my post "VDO Fuel Sender Woes."
There have been a number of reports of the insulator becoming loose and leaking, or even completely falling out after a period of time. In my case, after about 9 years, both of my sender insulators started crumbling and leaking. FWIW, I run 93 octane no-ethanol Mogas about 95% of the time, but failures have been reported with Avgas, too.
These senders were originally designed for mounting on top of a gas tank. I don't know if the side-mount's exposure to constant pressure from fuel contributes to the insulator deterioration and leak, but it apparently is not a rare event. I replaced my senders with Stewart Warner senders, which are similar (same mounting method and hole pattern) but a much-improved design in my opinion. Van's Aircraft uses these SW senders and also recommends NOT using the rubber gasket and seal them with Pro-Seal instead.
I supposed if top-mounting the VDO senders and designing-in access covers, it would not be necessary to use the Pro-Seal as it would be much easier to change them out if problems developed.
John
N750A
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Hey John.
I installed my SW senders with the rubber gasket and am just about to mate the wings to the fuse for the first time. Now I’m second guessing the sender installation. I did a 3 day leak test on each tank but that doesn’t mean much for the longer term. I’ve never used Pro-seal but if I’m going to go that way, now is the time. Any links to some good info on using it on our tanks/senders?
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Hi John B,
Although he top-mounted the senders, I think Mark's Kitplane Enthusiast Video's are the most helpful. Also, some searches on the web will turn up numerous posts about using the sealant - as I said earlier, Van's RV uses the SW senders and recommends using ProSeal. I used Spruce's ChemSeal (which is the same thing as ProSeal) and used the B2, which gives you about a 2 hour pot time. I found this plenty of time to install both senders before the sealant set up. With slight modifications, you can use a regular caulk gun to express the cartridge contents. In the RV's they're also mounted on the side of the tank rather than the top, so the experience and information is relative and valid. The RV builders frequently recommend hex cap screws to mount the sender - probably would make it easier to get a sealed screw out if you ever had to change the senders. One of our members told me he used those senders and ProSeal in his RV 20+ years ago and no problems with leaks - ever!
John
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