05-30-2012, 04:44 AM | #41 |
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Re: Vapor lock!
You know, it should make 'one ponder just why this topic of "vapor lock" is so controvercial. If you think about it, even float-a-motor mount or motor oil discussions here do not create the stir like this topic does. It is almost like folks want to fight about it to prove it can, -or cannot happen to them!! I find it even more ironic that apparently if someone raises the octane level of the fuel in the tank, the issue seemingly goes away?
The other thought I ponder is folks are basing this issue now on the ethenol laced fuels. Back a few decades ago when vapor lock was an issue, what was the blame then? Ethenol fuel?? |
05-30-2012, 05:01 AM | #42 | |
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Re: Vapor lock!
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05-30-2012, 05:15 AM | #43 | |
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Re: Vapor lock!
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05-30-2012, 07:33 AM | #44 |
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Re: Vapor lock!
You can call it what you like, but my 28 coupe does not run good after it sits and is restarted in hot weather. I have put a phenolic spacer between carb and manifold. Also rapped the gas line and fuel bowl. This has made a big difference. It never did this until the crap gas came out. In my case I think the manifold heater puts a lot more heat in the engine compartment. But it has been on the car since it was new in Mich. Also it feels real good in the winter time. So if it is not vapor lock, it is caused from the heat, and poor gas.
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05-30-2012, 07:54 AM | #45 | |||
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Re: Vapor lock!
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I have the same confusion... Since fuel is heavier than vapor, it should flow downward while vapor bubbles upward. The vapor should eventually make it's way back to the gas tank. The "pressure" explanation above doesn't seem likely. Why wouldn't the fuel continue to flow down past the vapor? Gravity is the only factor at play here, right?
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05-30-2012, 08:16 AM | #46 | ||
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Re: Vapor lock!
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Ok I am, ...and have been in the same mindset. To me, this is why we always get into these discussions yet there is never any resolve. Can someone not explain EXACTLY what is happening to cause this? In other words, exactly what is the heat doing, ...or what exactly is happening with the poor gas that is causing this? I would like to understand more than just someone saying "it turns into a vapor." . |
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05-30-2012, 09:45 AM | #47 | |||
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Re: Vapor lock!
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If you want a more scientific explanation, I think it has to do with surface tension of bubbles. Before a big bubble, like that under a drain plug in an inline filter, can either squeeze by the plug or up a skinny fuel line, it has to undergo an energetically unfavorable decrease in radius of curvature. I'm not saying I totally buy it, but if someone needs a theory before they can believe their eyes, there you go. Regarding your percolation theory, I don't doubt that a bit of sticky stuff will be left when gasoline evaporates. The part I don't understand is how that sticky stuff gets up on the shut-off valve when the evaporating puddle must be primarily down in the bottom of the bowl. Semantics: This isn't important but I don't underdstand use of the term "percolation" to describe boiling off the fuel in a carb bowl; as I understand it, it's not much like what goes on either in a percolator coffee pot or in a septic bed perc test. I realize that our use the term "vapor lock" to refer to any issues deriving from unwanted fuel vaporization (including percolation) also can be criticized. Earlier you asked how riding the choke could possibly help a vapor lock situation. My guess is that it simply takes what meager fuel is available and adjusts the air/fuel mix ratio to something more useable. Clearly, as you say, if there were complete "lock" of fuel flow, it wouldn't help, at least not for very long. So many threads--so little time. Steve |
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05-30-2012, 10:07 AM | #48 |
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Re: Vapor lock!
It's short notice, but since the MARC meeting is in Oshkosh next month, why not invite a guest speaker to shed some light on the subject? Someone local with extensive experience in thermodynamics and heat transfer would be ideal....someone who knows the difference between vapor and gas. Two potential candidates would be Richard Goldstein and Ephraim Sparrow from the University of Minnesota. Both of these guys are experts in heat transfer and thermodynamics with a lifetime of theoretical, scientific, and practical experience.
I don't have any experience with vapor lock...but get tired of all the bloviating. Just do whatever it takes to get your vehicle running. |
05-30-2012, 10:47 AM | #49 |
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Re: Vapor lock!
Walt had the same EXACT EXACT on the money problem as you.. Here is what WE did to correct it..
Drained the gas tank and filtered the gas, seems many time and it was a problem with an old cork that was flaking and blocking the fuel CLEANED thoroughly the carb and all the jets, removed and cleaned all of them, cleaned fuel bowl and added NEW Filter FINALLY. Changed the Gas cap to one that is vented properly NEVER EVER had a problem since Mark'
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05-30-2012, 11:36 AM | #50 |
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Re: Vapor lock!
Here's another thought:
For those of you going to Oshkosh, you might have an opportinuty to learn about vapor formation and fuel delivery. Since the meeting is at the EAA grounds, look around and see if there are any exhibits/posters that metion vapor formation, deviation from ideal air:fuel ratio, oxygenation, altitude, or whatever dealing with reliable fuel delivery and combustion. Aircraft engineers and pilots have experience with this topic. |
05-30-2012, 02:06 PM | #51 |
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Re: Vapor lock!
I wonder if these fuel problems happen more often on cars with cast iron or glass sediment bowls??? There's probably a reasonably common cause, if we can discover it. One poster has 2 cars that never do it & 1 car that DOES it. All 3 cars have common stock equipment. Bill W.
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05-30-2012, 02:24 PM | #52 |
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Re: Vapor lock!
An excellent point and your common sense/historical perspective trumps the thoughts of these folks. The volativity of a liquid is the factor, and ethanol added to gasoline lowers the volativity. In other words, ethanol makes engines run less efficiently but lowers the occurence of vaporization of the fuel.
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05-30-2012, 02:53 PM | #53 | |
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Re: Vapor lock!
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Hyperphysics - Georgia State University "The cohesive forces between molecules down into a liquid are shared with all neighboring atoms. Those on the surface have no neighboring atoms above, and exhibit stronger attractive forces upon their nearest neighbors on the surface. This enhancement of the intermolecular attractive forces at the surface is called surface tension." "Molecules liquid state experience strong intermolecular attractive forces. When those forces are between like molecules, they are referred to as cohesive forces. For example, the molecules of a water droplet are held together by cohesive forces, and the especially strong cohesive forces at the surface constitute surface tension. When the attractive forces are between unlike molecules, they are said to be adhesive forces. The adhesive forces between water molecules and the walls of a glass tube are stronger than the cohesive forces lead to an upward turning meniscus at the walls of the vessel and contribute to capillary action." Hope this helps. |
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05-30-2012, 03:15 PM | #54 | |
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Re: Vapor lock!
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Bill W.'s comparing the fuel line with a human esophagus is off the mark. Our beloved Model A's are not living organisms. Simple question, what would keep a vapor bubble from passing up through the fuel line and venting through the gas tank? Perhaps a high spot in the fuel line ,trash in the line, bad fuel cap, something like that. |
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05-30-2012, 03:25 PM | #55 | |
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Re: Vapor lock!
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Hyperphysics - Georgia State University "The process of evaporation in a closed container will proceed until there are as many molecules returning to the liquid as there are escaping. At this point the vapor is said to be saturated, and the pressure of that vapor (usually expressed in mmHg) is called the saturated vapor pressure. Since the molecular kinetic energy is greater at higher temperature, more molecules can escape the surface and the saturated vapor pressure is correspondingly higher. If the liquid is open to the air, then the vapor pressure is seen as a partial pressure along with the other constituents of the air. The temperature at which the vapor pressure is equal to the atmospheric pressure is called the boiling point." Now that we have vaporized fuel in a closed space, tension, cohesion and adhesion take over to finish the drama as explained in my previous post for newshirt. This may/probably doesn't meet your EXACT standards but it is the best this physics lovin, chemistry dropout can do. Like I mentioned before, I didn't believe a gravity system could vapor lock. |
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05-30-2012, 03:30 PM | #56 |
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Re: Vapor lock!
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05-30-2012, 08:09 PM | #57 |
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Re: Vapor lock!
I had this happen quite a bit last summer 105 out if i was at a red light to long it would vaper lock i just unscrew the drain plug let it flow fr one sec and cool carb as soon as temp outside drops a bit ie from day time to night the problem goes away up in ossipee NH you could still get real gass if i used real gass no problem rember alcohal boils at 160 degrees very posible for the temp under the hood to reach 160 very easey on hot day then all the alcohal in the line boils and causes vaper lock
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05-31-2012, 09:01 AM | #58 | |
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Re: Vapor lock!
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Technically, this is not vapor lock since the bubble is air, not vapor. But otherwise it is a good example of how a bubble can block gravity driven flow of liquid even when the system is open to the atmosphere above and below. Such a bubble can form in an inline fuel filter, which is what the original question was about. I believe that the basic explanation for the blockage in the face of gravity is surface tension. Steve |
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05-31-2012, 09:06 AM | #59 | |
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Re: Vapor lock!
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05-31-2012, 01:48 PM | #60 | |
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Re: Vapor lock!
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This is a prime example of surface tension, however, in this example the root cause of the trapped air bubble is usually a non-operational vent pipe. If the drain is properly vented the vents can sometimes accumulate leaves in the pipe and cease to work properly. |
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