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Old 05-11-2015, 08:40 AM   #11
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Originally Posted by bansil View Post
crawl under bus and look at tank, see if there is a rubber line coming from top of tank and draped over the side, I have actually pressurized my tank to a couple pounds using a tapered plastic fitting for inner tubes and air mattresses, stuck in that vent hose when filling new filters and bleeding injector lines (do not over pressurize!!!)
As I read the first portion, I thought you were talking about filling inner tubes and air mattresses from the gas fumes in the tank. I can picture that. Not good.:icon_e_surprised: Glad you clarified.
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Old 05-11-2015, 11:06 AM   #12
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A geeky, colored glasses goatee wearing...HippY , or maybe a techy guy ????


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Old 05-12-2015, 07:23 PM   #13
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I was not able to find a tube hanging over the side of the tank, i called a couple of truck places here in town but they had no reference book.
I put a regular pipe cap on it.

If it is supposed to be vented cap will I notice a vacuum if it is running and I hold my hand over the tube?
maybe a piece of plastic bag?
thanks
Cliff
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Old 05-12-2015, 11:33 PM   #14
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Originally Posted by c_hasbeen View Post
. . . I put a regular pipe cap on it.

If it is supposed to be vented cap will I notice a vacuum if it is running and I hold my hand over the tube?
maybe a piece of plastic bag?
thanks
Cliff
If it is supposed to be vented but is not, I don't think the fuel draw will be fast enough to feel suction on your hand, but I may be wrong. But once the engine pumps enough fuel out, there will usually be a vacuum that will prevent drawing any more and seem like you ran out of fuel.

As a result, you open the cap and see there is indeed fuel, put the cap back on and voila!, the engine starts and runs again until it doesn't. My snowblower lost a vent spacer in its cap this winter, and with the cap on tight it was pulling this trick until I figured it out.

On the sheet metal passenger car tanks, I have heard that with a strong enough fuel pump the vacuum can collapse the tank instead of starving the engine. But the heavy tank on a bus should be strong enough to resist this.

If the engine will run for an hour with the un-vented pipe cap on the tank, you should not need to add a vent and be good to go.

If you have any doubts, a pinhole in the pipe cap would relieve the vacuum. I'm guessing that 1/8 inch or even smaller might do the trick. I would maybe even start with 1/16 inch. If the bus idles and cruises fine, but seems to starve going up long hills unless you take your foot off the throttle, you might gradually enlarge the vent until you have continuous power at all loads.
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Old 05-13-2015, 07:14 AM   #15
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Sounds like great advice Redbear
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Old 05-17-2015, 09:11 AM   #16
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I forgot to add that the effect is greater when the tank is full of fuel, and not nearing empty. If a vacuum is formed, a near-empty tank would try to expand a lot of air just a little bit, and may not cause fuel starvation.

A vacuum caused in a near-full tank would need to expand the little bit of air a lot, and cause a multiplication of the pressure drop and its effects.
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