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Old 25th March 2010, 15:29   #1
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Default Fuel tank quantity sensing Mechanism on dispensing machines .

Many of us are not aware that the petrol kiosk pump has a return pipe-line (in Pink ).. When the petrol tank (in the car) reaches full level, there is a mechanism to trigger off the pump latch and at the same time a return-valve is opened (at the top of the pump station) to allow excess petrol to flow back into the sump. But the returned petrol has already passed through the meter, meaning you are donating the petrol back to SHELL/CALTEX/MOBIL/ PETRONAS


I just got this E mail as a forward , Gurus Please throw some light to this and assure the credibility.

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Old 25th March 2010, 15:38   #2
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Thats sheer daylight robbery if its true. How would a common man know if he is being charged for something he has not taken. Maybe the meter should be at the tip of the nozzle.
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Old 25th March 2010, 15:56   #3
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What an apt time for this thread ! I fill up my tank every Sunday and for the last two weeks I have been noticing that despite the tank being full (auto cut-off) the needle in the fuel gauge does not touch the 'F' mark. It has never been like this before and is strange. I was wondering if I should get my fuel gauge checked and now I bump into this thread.
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Old 25th March 2010, 16:15   #4
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so what you are saying is that after the cutoff, more petrol is filled, the same amount will return back from the car fuel tank to the pump fuel sump.

so then, how come after the cutoff, if we fill too much petrol too fast, it some time comes up and spills out of the fuel cap. this would never happen if it were returning to the pump fuel sump.

the authenticity of this claim should be checked coz it doesn't make any sense.

UM
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Old 25th March 2010, 16:18   #5
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This may hold good for the newest petrol dispensing machines , so just to check please check with Shell in India.
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Old 25th March 2010, 16:19   #6
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I doubt it. I've seen the way the machine cuts fuel. It happens the moment the fuel touches the metal part of the fueling hose and the fuel level in the tank does not go down after that.

You could try filling it to the brim. There is very little room inside the fuel tank inlet pipe, so even if a slight amount of fuel is taken back, the level will drop drastically.

I usually top up at BP, HP or IOC so don't know how shell pumps work, but the filling to the brim technique should give you fair visual idea.

Shan2nu

Last edited by Shan2nu : 25th March 2010 at 16:23.
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Old 25th March 2010, 17:12   #7
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I think auto cut works on the mechanism of lubrication whenever fuel with come up full in tank the level pulls out because of fluid (petrol) in between. Correct me if I am wrong...
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Old 25th March 2010, 17:25   #8
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This is hard to believe.

From what i googled, i found an interesting article which would clear the doubts about the modern day fuel dispensing Machine.
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File Type: pdf Fuel Pump Dispensing Machine.pdf (1.60 MB, 2441 views)
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Old 26th March 2010, 17:53   #9
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That mail you have recieved is absolutely INCORRECT! Let me tell you for a fact there is no return pipe into the tank from the machine In any Petrol Pumps in india be it IOC,BPCL,HPCL or shell

There is just one pipeline from the tank to the machine which is connected to the motor which is then connected to the head assembly then the Hose and last but not the least to the nozzle.

When the nozzle cuts off what ever the meter shows is what is actually there in your fuel tank.

Last edited by Born 2 Be Wild : 26th March 2010 at 17:55.
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Old 26th March 2010, 18:18   #10
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Quote:
Originally Posted by Born 2 Be Wild View Post
That mail you have recieved is absolutely INCORRECT! Let me tell you for a fact there is no return pipe into the tank from the machine In any Petrol Pumps in india be it IOC,BPCL,HPCL or shell

There is just one pipeline from the tank to the machine which is connected to the motor which is then connected to the head assembly then the Hose and last but not the least to the nozzle.

When the nozzle cuts off what ever the meter shows is what is actually there in your fuel tank.
Minus the amount of fuel still remaining in the pipe - from the nozzle till wherever the sensor is which indicates the quantity dispensed..
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Old 26th March 2010, 19:06   #11
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Quote:
Originally Posted by sanjayc View Post
Minus the amount of fuel still remaining in the pipe - from the nozzle till wherever the sensor is which indicates the quantity dispensed..
The Fuel sensor is located right above the Head assembly and the Nozzle till the fuel sensor is calibrated hence when people refuel the pipe is fully loaded till the nozzle so what you pay for is what you get if the Dispenser is properly calibrated.
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Old 26th March 2010, 21:55   #12
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Quote:
Originally Posted by Born 2 Be Wild View Post
The Fuel sensor is located right above the Head assembly and the Nozzle till the fuel sensor is calibrated hence when people refuel the pipe is fully loaded till the nozzle so what you pay for is what you get if the Dispenser is properly calibrated.
Great..that's very comforting to know.
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Old 26th March 2010, 22:06   #13
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Are you telling after the cutoff whatever fuel remains in the fueling pump (yellow pipe) will go back to the sump.

Hm.. if thats the case how much fuel ? depends up on the length/dia of that tube and the quantity it can hold.
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Old 17th September 2013, 12:29   #14
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Default Re: Fuel tank quantity sensing Mechanism on dispensing machines .

1 L = 1000 cc.

Assuming a thick pipe of diameter 6 cm, this would mean approximately every 35 cm of pipe will hold 1 L of fuel. Now it will depend on the length of pipe, if the fuel does go back. (1 m = 3 L of fuel; quite likely people will notice this scam as 3 L is about 7-10% of the capacity of most small cars)
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Old 17th September 2013, 14:00   #15
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Default Re: Fuel tank quantity sensing Mechanism on dispensing machines .

It is unlikely that there will ever be clarity on this issue as we won't have an concrete evidence unless someone inspects a few pumps. I guess to be on the safe side one should not encourage filling any excess fuel once the auto cut-off mark is reached.
I always try and follow this as squeezing a few 100ml extra can result in excess gases being formed in the tank thereby resulting in an overspill that could damage your paint.
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