BUBBLES

Submitted: Friday, Oct 20, 2017 at 11:46
ThreadID: 135771 Views:2910 Replies:11 FollowUps:6
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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
Muzbry
Great place to be Mt Blue Rag 27/12/2012

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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.
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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: Michael H9 - Friday, Oct 20, 2017 at 12:46

Friday, Oct 20, 2017 at 12:46
I'm wondering if we pay for the space the bubbles take up when each litre passes through the pump? 0.9 litres of diesel, 0.1 litres of bubble (or worse) for each litre.
AnswerID: 614460

Follow Up By: Member - kimberleybloke - Friday, Oct 20, 2017 at 13:36

Friday, Oct 20, 2017 at 13:36
G'day Michael, in a nutshell all diesel pumps that sell to the public must have an air separation/elimination device before the meter that measures the fuel. Also before the meter on a diesel pump there will be an air detection shut off device/valve, that will stop the flow of diesel completely if it detects any air mixed in with the fuel before it reaches the metering unit. Fuel will not flow again until all the air has been eliminated. In most situations you can be confident that only fuel is being measured. Companies that repair/calibrate diesel pumps must test that these systems are operating before recertifying a pump for public use. Having said that, the shut off systems can be tampered with, (even though they should have a repairers seal affixed) If anyone thinks something is a bit fishy, ie really aerated fuel coming out of the spout, you could contact your state trade measurement people and ask them to check said pump.
Regards, Mark.
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Reply By: Allan B (Sunshine Coast) - Friday, Oct 20, 2017 at 15:03

Friday, Oct 20, 2017 at 15:03
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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.
Cheers
Allan

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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: axle - Friday, Oct 20, 2017 at 20:12

Friday, Oct 20, 2017 at 20:12
Muzbry,,, Stop topping it up with lemonade!!....LOL



Cheers Axle.
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Follow Up By: RMD - Friday, Oct 20, 2017 at 20:51

Friday, Oct 20, 2017 at 20:51
If it’s froffy then it may be something other than lemonade.
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Reply By: 9900Eagle - Saturday, Oct 21, 2017 at 05:33

Saturday, Oct 21, 2017 at 05:33
Here you go Muzbury, this should do your head in.

Bubbles link
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Reply By: MUZBRY- Life member(Vic) - Saturday, Oct 21, 2017 at 08:30

Saturday, Oct 21, 2017 at 08:30
Good morning
Thanks fellas, thats exactly what i was thinking. It just doesn't matter.
Muzbry
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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



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Reply By: member - mazcan - Sunday, Oct 29, 2017 at 13:29

Sunday, Oct 29, 2017 at 13:29
I can remember fuelling up our caterpillar D2 tractor tank when I was only 14yrs old with a hand drum pump and the diesel had air bubbles in it in those days nothing has changed still the same today doesn't matter whether you pour it or pump it always has air bubbles
AnswerID: 614638

Reply By: greybeard - Sunday, Oct 29, 2017 at 15:30

Sunday, Oct 29, 2017 at 15:30
The diesel pump was invented by the same bloke who invented the beer tap.
AnswerID: 614642

Reply By: Member - Roachie - Sunday, Oct 29, 2017 at 17:32

Sunday, Oct 29, 2017 at 17:32
Watch this......

https://www.youtube.com/watch?v=x4LCbGsujdU&t=203s

This is the type of pump and filtration system I use on my Silverado.
AnswerID: 614643

Reply By: Allan B (Sunshine Coast) - Sunday, Oct 29, 2017 at 20:25

Sunday, Oct 29, 2017 at 20:25
.
I think that there may be some confusion here between "bubbles" and "froth". And Muzbry did ask about bubbles.
Cheers
Allan

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Follow Up By: MUZBRY- Life member(Vic) - Sunday, Oct 29, 2017 at 21:16

Sunday, Oct 29, 2017 at 21:16
Gday Alan
Arnt bubbles froff ?. I must say that the bubbles i was asking about could be called froth . But like i said earlier, "it just does not matter"
Muzbry
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