vented vs. non-vented....

Discussion in 'Motorized Bicycle General Discussion' started by tommyboy1442, Feb 20, 2010.

  1. tommyboy1442

    tommyboy1442 Member

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    whats up there norm, was wondering if you might know, i was wondering if it is possible to run a non-vented fuel cap. can this cause problems? will it affect the way the fuel flows? if i were to run a non-vented, will i be able to run the petcock not at the lowest point of the tank and still be able to flow all the fuel out of the tank? i was thinking if its non-vented the pressure will push the fuel from the lowest part of the tank to a higher point where the fuel petcock would be located. will this work? is there any hazards as far as non vented? what is an application where a non-vented cap might be used other than diesel. thanx for any input given. rock on....
     
  2. K.i.p

    K.i.p New Member

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    Put a straw into a glass of soda. Place a finger tip over the exposed end of the straw. (No vent) Lift the straw and notice how the soda does not exit the straw but rises above the fluid level. Take your finger off the straw and the fluid drops back down into the glass. (Vented)
     
  3. bairdco

    bairdco a guy who makes cool bikes

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    if it's not vented, you'll get vapor lock, which is the same as the fuel being off.

    my copper tank wasn't venting right, and it would sputter and die unless i cracked open the cap now and then. when sitting, fuel would start to seep out of the base of the gas cap, because it had too much pressure in it.

    i had to drill a tiny hole in it. now, it runs fine, and there's just the smallest druibble of fuel to worry about on the tank.
     
  4. corgi1

    corgi1 New Member

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    They got to be pullin your leg,lol,,you got to run a small air compressor to the tank to force the fuel down to the crankcase where it mixes w/oil and returns to the tank so that it can go through the carb and mix w/air then something else happens and if your still around the engine might start,,,ROFLMAO
     
  5. corgi1

    corgi1 New Member

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    Sorry ,I got carried away,I'll try to be good
     
  6. Nougat

    Nougat New Member

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    Every fuel tank is vented. You can't take fuel out of the tank for very long without putting something back in to replace the volume of space that the used up fuel is no longer displacing. If the tank wasn't vented, the negative pressure inside would build to the point that either fuel would stop flowing out of it, or the tank would collapse.

    BMW 7-series used to do this in the 90s, the tank venting would fail and the tank would collapse. Train tanker cars have safety valves to prevent them from collapsing in the same way. What happens if that valve doesn't work? Something like this: YouTube - Implosion of a train tanker car - must see !

    Cars have vent tubes that run back to the fuel system on the engine, so that no fuel fumes escape into the air. They also have a carbon filter on that vent tube, also for emissions purposes. So, yes, you can run with a non-vented cap, but you cannot run without fuel tank venting.
     
  7. tommyboy1442

    tommyboy1442 Member

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    so ive seen nonvented fuel caps but didnt keep in mind that the tank is vented.after seeing this video, i believe i will be buying a vented fuel cap. thanx that was interesting.
     
  8. 2door

    2door Moderator
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    That tank car didn't just implode from being drained. It was evacuated by means of high volume vacuum pump lowering the internal pressure, probably something in the neighborhood of 20 plus inches, enough that only 14.7 psi, atmospheric pressure, collapsed it. Nothing like this could happen to a bicycle fuel tank because there is nothing 'sucking' the fuel out. It would take a good fuel pump, and a poorly made fuel tank to collapse a tank like the rail car. Tank cars are designed to withstand positive internal pressure, not a negative pressure. Rapid temperature changes can cause collapse of some vessles if conditions are right, such as reduced internal pressure and rapid application of heat/cold to the outer surface.
    Tom
     
  9. corgi1

    corgi1 New Member

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    You don't think heating the train car ,closing the lid and pushing it out in the cold winter weather would smash it like the 55 gallon drum on another vidio :confused:
     
  10. 2door

    2door Moderator
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    NO...........................
     
  11. corgi1

    corgi1 New Member

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    Well its 30 out side and dropping I think I will sneak down to the switching yard and..................
     

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