The Naked Scientists

The Naked Scientists Forum

Author Topic: How Accurate Are Petrol/Gas Pumps ?  (Read 10138 times)

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • Posts: 20602
  • Thanked: 8 times
    • View Profile
How Accurate Are Petrol/Gas Pumps ?
« on: 20/09/2011 11:00:07 »
Over here in goold ole UK...our non UK chums might be interested to know that we can purchase a whole litre of petrol/gas for only $2.20 !!!! (Sept 2011)...Yep...ewe read that right well over two dollars for a friggin litre !!


So, ewe can imagine why I wonder that when I fill my tank up that I am getting what I have paid for !


I want to know is how accurate are the pumps at measuring a litre of fuel ?....Could i be losing out even more ?..or gaining ?

How do they measure the litre ?



Whilst filling up my car I asked a typical girlie driver if she knew and this was her response !





A Typical Girlie Driver Yesterday !





As ewe can see....no luck there !!  ::)






Do ewe know how accurate pumps are and how they measure the litre ?


Ta


Neil
Fed Up With Fuel
xxxxxxxxxxxxxxxx








 

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • Posts: 20602
  • Thanked: 8 times
    • View Profile
How Accurate Are Petrol/Gas Pumps ?
« Reply #1 on: 20/09/2011 11:01:08 »
...also...what do ewe pay for a litre of gas ?
 

Offline techmind

  • Hero Member
  • *****
  • Posts: 934
  • Un-obfuscated
    • View Profile
    • techmind.org
How Accurate Are Petrol/Gas Pumps ?
« Reply #2 on: 20/09/2011 11:39:55 »
I don't know about the accuracy of dispensing, but I did discover a curious glitch in the system a couple of years back ... when petrol was advertised as costing £1.00 per litre...

I bought "10.00" litres of fuel and it cost £10.01.    ::)

Doncha just love computers and rounding errors! The girl at the till said some other customers has noticed the same thing.
 

Offline peppercorn

  • Neilep Level Member
  • ******
  • Posts: 1466
    • View Profile
    • solar
How Accurate Are Petrol/Gas Pumps ?
« Reply #3 on: 20/09/2011 11:43:31 »
I've heard it claimed that you will get raw deal if you fill up on a hot summer's day compared with a cold (let's assume, winter's) day.  This is due to the expansion of the fuel - so we'd be better off if we could buy fuel by the kilogram, I guess!

It's a while since I filled up on petrol (or gas') and as I just sold my car it probably won't be something I'll be doing again for a while longer.
 

Offline damocles

  • Hero Member
  • *****
  • Posts: 756
  • Thanked: 1 times
    • View Profile
How Accurate Are Petrol/Gas Pumps ?
« Reply #4 on: 20/09/2011 11:53:19 »
Our irrigation channels (not the main ones, but the little ones in the offtake to individual properties) have/used to have paddle wheels in them that turned to measure the water flow. I had always imagined that the older style water meters and petrol dispensers worked in a similar way. I can remember one fuel company had bowsers where you could see the little paddle turning in a glass hemisphere on the side of the bowser. But this style of meter seems to have been replaced with something electronic and I too would be interested to know how the modern ones work.

How accurate they are is really a matter for the weights and measures legislation and enforcing authorities, but I seem to recall that here (in Oz) there is a surprisingly large tolerance, something like 5%!

Petrol prices have gone up a lot here in the last couple of years; at present they are around $1-50 per litre. (At present $A is very close to $US).
 

Offline Geezer

  • Neilep Level Member
  • ******
  • Posts: 8328
  • "Vive la résistance!"
    • View Profile
How Accurate Are Petrol/Gas Pumps ?
« Reply #5 on: 21/09/2011 03:21:18 »
Yes, I think the flowmeters in the pumps measure by volume, so you do get a bit less when the petrol is warm, but it's not much of a difference. The best pumps were probably the really old ones where you could see the fuel you were getting in a big glass tank on top of the pump.

In these parts, regular gasoline is currently going for about $3.70 a US Gallon, which is almost four litres. That puts it at less than half of what Sheepy has to shell out. I think he's getting fleeced.

At those prices you might be better running your car on ouzo. BTW, that girlie isn't by any chance Prunella Cholmondeley-Marjoribanks?


For further reading

http://en.wikipedia.org/wiki/Fuel_dispenser#The_metrology_of_gasoline
http://en.wikipedia.org/wiki/Flow_measurement
« Last Edit: 21/09/2011 03:49:59 by Geezer »
 

Offline MikeS

  • Neilep Level Member
  • ******
  • Posts: 1044
  • The Devils Advocate
    • View Profile
How Accurate Are Petrol/Gas Pumps ?
« Reply #6 on: 21/09/2011 11:16:08 »
UK petrol pumps always used to be positive displacement pumps and checked regularly by customs and excise.
Petrol in Bulgaria is 2.48 lev per litre, that's 1.11GBP or 1.73USD
 

Offline CZARCAR

  • Hero Member
  • *****
  • Posts: 686
    • View Profile
 

Offline SeanB

  • Neilep Level Member
  • ******
  • Posts: 1118
  • Thanked: 3 times
    • View Profile
How Accurate Are Petrol/Gas Pumps ?
« Reply #8 on: 21/09/2011 16:33:55 »
The flowmeters are accurate, but as the pump ages they do wear and lose accuracy. The shiny outside is nothing, the metering pump inside could be 60 years old, be a shaft that is calibrated initially to give one turn per quart, but is connected to a modernised counter to give price in pounds per litre or dollars per gallon or whatever. They do suffer from 2 problems, varying temperature and wear causing fuel to bypass internally, both causing an error. Temperature of the bulk fuel is pretty constant, as it is stored in a underground tank at close to ground temperature. Best is to fill a day after the tanker has replenished, both because the fuel will have cooled to ground temperature and because the water and other dirt will have separated out of the fuel and will not be in the supply that you get. As to the wear, I knew of a pump that, whilst passing the calibration test where they fill a known volume tank from the pump at full flow, this one was worn, and would read very low if you restricted the flow rate to a very low level. I found this out from having a blocked tank breather, so had to fill at a low rate, taking 20 minutes to fill 40l into the tank. Pump read that the full tank was under 20l when I knew it would be around 38l, so I filled up there a few times, until the pump was replaced during modernisation of the forecourt. Not my problem, as I had shown the fault to the station manager, and the owner did little about it.
 

Offline CZARCAR

  • Hero Member
  • *****
  • Posts: 686
    • View Profile
How Accurate Are Petrol/Gas Pumps ?
« Reply #9 on: 21/09/2011 18:38:06 »
The flowmeters are accurate, but as the pump ages they do wear and lose accuracy. The shiny outside is nothing, the metering pump inside could be 60 years old, be a shaft that is calibrated initially to give one turn per quart, but is connected to a modernised counter to give price in pounds per litre or dollars per gallon or whatever. They do suffer from 2 problems, varying temperature and wear causing fuel to bypass internally, both causing an error. Temperature of the bulk fuel is pretty constant, as it is stored in a underground tank at close to ground temperature. Best is to fill a day after the tanker has replenished, both because the fuel will have cooled to ground temperature and because the water and other dirt will have separated out of the fuel and will not be in the supply that you get. As to the wear, I knew of a pump that, whilst passing the calibration test where they fill a known volume tank from the pump at full flow, this one was worn, and would read very low if you restricted the flow rate to a very low level. I found this out from having a blocked tank breather, so had to fill at a low rate, taking 20 minutes to fill 40l into the tank. Pump read that the full tank was under 20l when I knew it would be around 38l, so I filled up there a few times, until the pump was replaced during modernisation of the forecourt. Not my problem, as I had shown the fault to the station manager, and the owner did little about it.
Ever seen an above ground storage tank?
 

Offline SeanB

  • Neilep Level Member
  • ******
  • Posts: 1118
  • Thanked: 3 times
    • View Profile
How Accurate Are Petrol/Gas Pumps ?
« Reply #10 on: 22/09/2011 10:14:46 »
Yes, but only on either a farm or in a business, where it is used to detote fuel that already has been paid for, into either farm, construction or business vehicles. It is not really relevant here as you are merely recording for either monitoring or not at all, but are not using the information for billing purposes. Your supplier is dispensing into your tank with a calibrated meter, but the flowmeter going out of the tank may not have been calibrated for years aside from the initial factory calibration.
 

Offline Geezer

  • Neilep Level Member
  • ******
  • Posts: 8328
  • "Vive la résistance!"
    • View Profile
How Accurate Are Petrol/Gas Pumps ?
« Reply #11 on: 22/09/2011 17:18:25 »

Ever seen an above ground storage tank?


The gas station nearest to me has above ground tanks that were installed a couple of years ago. I think they are preferred these days because they are less likely to contaminate ground water.
 

Offline damocles

  • Hero Member
  • *****
  • Posts: 756
  • Thanked: 1 times
    • View Profile
How Accurate Are Petrol/Gas Pumps ?
« Reply #12 on: 22/09/2011 18:39:02 »
Quote
Quote from: CZARCAR on 21/09/2011 18:38:06

Ever seen an above ground storage tank?


The gas station nearest to me has above ground tanks that were installed a couple of years ago. I think they are preferred these days because they are less likely to contaminate ground water.

:o

I guess it would give you a better chance of detecting a leak!
 

Offline SeanB

  • Neilep Level Member
  • ******
  • Posts: 1118
  • Thanked: 3 times
    • View Profile
How Accurate Are Petrol/Gas Pumps ?
« Reply #13 on: 22/09/2011 18:56:11 »
Here all filling stations are owned by the relevant oil company, there are no independent retailers. They all use underground tanks, that are checked and replaced at regular intervals, with both an outer barrier and a drain layer with inspection and drain lines. Mostly from a safety and security standpoint, as it is very difficult for an underground tank to contribute to a fire, even if the piping is broken. Above ground tanks are almost always either on private ground or on a trailer.
 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
How Accurate Are Petrol/Gas Pumps ?
« Reply #14 on: 22/09/2011 20:38:44 »
Whew...  only $2.20 for gas in the UK...
It is just under $4 here...

Oh,
Was that per liter?

That is less than $4 per GALLON here!!!

Of course, US Liquid gallons are smaller than either British Imperial Gallons...  or the equivalent of 4 liters.

Anyway, the old analog pumps would read down to a tenth of a gallon, although perhaps the accuracy is higher than that, especially if they are capable of penny sales, or approximately 1/400 of a gallon (it is hard to squeeze off a penny on the pump handle though).

I believe the newer pumps read in hundredths of a gallon.

Most commercial weights and measuring devices have to be periodically calibrated.  I haven't paid much attention to it, but I believe there are calibration tags on all fuel pumps in the USA. 

Hmmm...  1/10 of a gallon would be about 40 cents.  whew. 
1/100 gallon would still be about 4 cents.
(Why are the charges still based on tenths of a penny?)

Anyway, there would be two types of accuracy.  The error in a continuous flow, and the error in a start/stop cycle.  If there are certifications, then somewhere there have to be certification standards.

Also, I believe the EPA is also monitoring the ins and outs of the underground storage tanks.  So, say they have a 10,000 gallon underground storage tank, the ins and outs should match up to somewhere within a gallon or so. 

Anyway, with a bit of sleuthing, one should be able to find the basic calibration standards, as well as the EPA ins/outs alarm triggers.

BTW, there is an above ground Diesel tank at a now closed neighborhood store about 1/2 mile from my house.  I assume the gasoline tank was below ground.
 

Offline Geezer

  • Neilep Level Member
  • ******
  • Posts: 8328
  • "Vive la résistance!"
    • View Profile
How Accurate Are Petrol/Gas Pumps ?
« Reply #15 on: 22/09/2011 21:26:02 »
Whew...  only $2.20 for gas in the UK...
It is just under $4 here...

Oh,
Was that per liter?

That is less than $4 per GALLON here!!!


Er, it's equivalent to $8.32 for a US gallon. That's more than double the price in most of the US.

BTW, why don't they trust you to pump your own gas?
 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
How Accurate Are Petrol/Gas Pumps ?
« Reply #16 on: 23/09/2011 03:20:52 »
BTW, why don't they trust you to pump your own gas?
Ahh...  yes, 
Oregon and New Jersey do not have self service gas.
Although, sometimes one can get away with pumping one's own Diesel.

Here is the Wikipedia Note:
All stations in New Jersey and Oregon offer only full service and mini service; attendants are required to pump gas because customers are barred by statutes in both states from pumping their own gas. New Jersey banned self-service gasoline in 1949 after lobbying by service station owners. Proponents of the ban cite safety and jobs as reasons to keep the ban.  Likewise, the 1951 Oregon statute banning self-service gasoline lists seventeen different justifications, including the flammability of gas, the risk of crime from customers leaving their car, the toxic fumes emitted by gasoline, and the jobs created by requiring mini service.  In addition, the ban on self-service gasoline is seen as part of Oregonian culture.

I've been across the country, and truthfully I don't really care.  It isn't supposed to save a lot of money.

My mother finds that it is awfully convenient to have someone else pump her gas.  And, I suppose that is good enough for me.  At my favorite station, they don't have the mini/full serve distinction, but if the attendant is not busy, they will wash the windows, although it has been years since anybody has offered to check my oil.

Here is a kind of long report about static electricity and fuel tank fires, although it appears to be somewhat less conclusive about the causes than one might expect.  However, it does indicate that some of the fires would be less likely if it was not self service. 

What about the number of people driving off with the filling hose still in the tank?  I've seen it happen in California, but never in Oregon.


The biggest issue that I've had with the Oregon law is that while most of the filling stations along the freeway are open 24/7, those away from the freeway aren't.  And, I have a tendency to drive at night. 

So, for example, from Bend Oregon to Ontario Oregon is about 261 miles of a fairly major, but secondary route, and not a single filling station is open late at night.  And, since the stations are not open, and without self service gas, one is out of luck.
 

The Naked Scientists Forum

How Accurate Are Petrol/Gas Pumps ?
« Reply #16 on: 23/09/2011 03:20:52 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums