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leaky screws

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cscsail(at)gmavt.net
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Posted: Wed Jan 18, 2006 8:23 am Post subject: leaky screws

Thanks for the input. I replaced the split paper washers and I have no leaks, as long as I don't put a grounding lug under the screw head. The washers I was provided are made of a thin gasket material with the integrity of heavy paper, and can only be snugged, or they will split.

The problem I see with using these sending units is trying to ground them properly. The units appear (when checked with an ohm meter) to have good continuity between them and the grounded tank --without a grounding wire and lug under a screw. For this to be the case, the edge of the screws probably makes contact with the edge of the holes in the sender since the screw heads are insulated from the surface with the paper washers--hardly a reliable bond, more like an accident. If I add a grounding lug so that it is resting on top of the sender and making good contact with the case and have a washer between it and the head of the screw, I will have a leak around the grounding lug. I could use permatex or similar goo, but I think it probably defeats the ability of the grounding lug to form a reliable bond. I may be over analyzing this problem, but it just seems like a bad installation. The units should probably have a tab soldered right to the case for proper bonding or copper crush washers may be the answer.

Still thinking about it,

Gordon

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mountain4don

Joined: 18 Jan 2006
Posts: 29

Posted: Wed Jan 18, 2006 11:00 am Post subject: leaky screws

Hello Gordon,

  

  I just got finished installing my VDO sending unit in one of my tanks  also, but have not filled it yet.  I noticed that you apparently  put the paper washer between the screw head and the ring terminal, with  the ring terminal now touching the face of the sender plate.   According to the instruction manual, on page 6-K-1B page 12 of 12, top  right hand corner of the page, the washer goes under the ring terminal  next to the plate.  Not like you described below.  Also the  screw is threading into the steel plate on the inside of the tank,  pressed pretty hard against the aluminum skin, and making a really good  electrical grounding connection there.

  

  Don

  601 XL, tail done, working on wings

  

  Thanks for the input. I replaced the split paper washers and I have no  leaks, as long as I don't put a grounding lug under the screw head. The  washers I was provided are made of a thin gasket material with the  integrity of heavy paper, and can only be snugged, or they will split.

  

  The problem I see with using these sending units is trying to ground  them properly. The units appear (when checked with an ohm meter) to  have good continuity between them and the grounded tank --without a  grounding wire and lug under a screw. For this to be the case, the edge  of the screws probably makes contact with the edge of the holes in the  sender since the screw heads are insulated from the surface with the  paper washers--hardly a reliable bond, more like an accident. If I add  a grounding lug so that it is resting on top of the sender and making  good contact with the case and have a washer between it and the head of  the screw, I will have a leak around the grounding lug. I could use  permatex or similar goo, but I think it probably defeats the ability of  the grounding lug to form a reliable bond. I may be over analyzing this  problem, but it just seems like a bad installation. The units should  probably have a tab soldered right to the case for proper bondin

 g or 

 copper cr!

  

  ush washers may be the answer.

  

  Still thinking about it,

  

  Gordon     

			

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_________________
Zenith 601XL, tail done, working on wings

cscsail(at)gmavt.net
Guest

Posted: Wed Jan 18, 2006 12:09 pm Post subject: leaky screws

Don,

    Your right that the steel baking plate is well grounded to the inside of

the tank and the screws themselves are now well bonded but there is no real

bond to the sending unit because it is isolated by the rubber gasket and

unless the screw touch the unit as they pass through the holes it is

isolated. Running a ground wire to the screw and isolating it from the

sending unit with a washer defeats the purpose of the ground wire.  I think

Michel has the right idea, but a more appropriate sending unit with a

grounding lug would probably be the best solution.

Gordon



---

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