BUBBLES
Submitted: Friday, Oct 20, 2017 at 11:46
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MUZBRY- Life member(Vic)
Gday
I was just wondering why there are so many bubbles in diesel when it pumps into the tank.There cant be bubbles in the pump because it would possibly cavitate . Just wondering
Reply By: RMD - Friday, Oct 20, 2017 at 12:08
Friday, Oct 20, 2017 at 12:08
The nozzle used on most pumps has a cutoff feature when the level reaches the nozzle. It has a detector which is loose in the small section of the nozzle dia.
When fuel passes over/past it it can draw a small amount of air into that section and that areates the fuel to some degree.
Fuel hitting corners and baffle plates or restrictions also areates the fuel as does dropping into the tank. As you fill the tank the return/exiting air comes out of the large breather into
the neck where the fuel is pumped in. That air, if it combines with the intake fuel flow, to some degree, but does so far more if the fuel is actually allowed to hit the air exit port into
the neck. That will definitely aerate the fuel as it fires directly into the fuel stream
So if the fuel is turbulated, and hits the exit air port + the amount the nozzle creates you will end up with a large amount of froth. Not allowing time for the fuel froth to subside means it becomes a problem for those in a hurry with little patience.
In a highflow truck tank the area in the tank is larger so more opportunity for the froth to dissipate before it gets to
the neck. They also have far less intake turbulation happening.
If filled quickly our vehicles require a slowdown of rate near the end to allow the froth to dissipate. Very slow after the first shutoff and there is no problem. Don't wear dark glasses when filling if you want to see the increasing level in the tank, other wise you see it on your pants when full.
AnswerID:
614456
Follow Up By: Member - Rod N (QLD) - Friday, Oct 20, 2017 at 12:33
Friday, Oct 20, 2017 at 12:33
Petrol doesn't do it so it must be something to do with diesel. I think BP advertises that their Ultimate fuel is low foaming.
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Follow Up By: RMD - Friday, Oct 20, 2017 at 15:45
Friday, Oct 20, 2017 at 15:45
Rod N
You are so right, petrol has a far different surface tension of the fuel compared to diesel and is thinner than diesel too, and also volatility of petrol is higher.
It is the diesel which foams so defiinitely something to do with diesel.
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Reply By: Allan B (Sunshine Coast) - Friday, Oct 20, 2017 at 15:03
Friday, Oct 20, 2017 at 15:03
.
G'Day Muz,
The bubbles you are observing are probably from the action of the cut-off valve within the filler nozzle.
There is a venturi within the nozzle arranged so that the flow of fuel creates a partial vacuum that draws air in via a small tube whose open end is positioned at the nozzle discharge opening. When the end of this tube is occluded by the rising fuel the pressure within the tube decreases and operates the cut-off valve.
The bubbles you see are the result of the air induced by the venturi being mixed into the fuel. It has no effect on the measured volume as the air is introduced after the metering.
AnswerID:
614463
Follow Up By: Member - Tony H (touring oz) - Friday, Oct 20, 2017 at 16:37
Friday, Oct 20, 2017 at 16:37
Well there you go......
I thought the bubbles was an 'indication' of the fuel quality....more bubbles lesser quality.....whenever I get BP Ultimate, I get very few if any bubbles??? (probably more anti foaming agent)
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Reply By: Bob Y. - Qld - Saturday, Oct 21, 2017 at 10:18
Saturday, Oct 21, 2017 at 10:18
Muz,
There is a direct correlation between foaming of diesel and the following:
The number of other vehicles waiting to use the one & only diesel pump;
The Impatience Factor of drivers of said vehicles;
The state of your clothes ie: are you going to a wedding/christening, or just slipping up to the yard to do a service on a D9?
Are there any disposable gloves left at said bowser;
Where are you planning to travel? If it's the Simpson/CSR, then you'll want the diesel lapping the flange at the filler spout, which might be difficult if you refer to points 1 & 2.
No doubt there's many other difficulties when the diesel is foaming?
Bob
AnswerID:
614490