Added a Hot Subject
The actual measurement of gasoline quantities is poorly understood and is currently the subject of a lot of loose talk in the Southwest US. I was looking for a PD picture of a dispenser with a glass vessel on top, the type that prevailed <1930 where the fuel was first pumped into the glass bowl for consumer inspection. I saw I could move this subject along also. After four shots, I was able to work an overview into it. —Preceding unsigned comment added by George5530 (talk • contribs) 17:26, 7 November 2008 (UTC)
Paul Deitch Contributions
Sorry but parts of this article are demonstrably wrong. I would like to collaborate with someone to correct them. Paul Deitch —Preceding unsigned comment added by Pdeitch (talk • contribs) 19:48, 27 August 2008 (UTC)
I have been working in the US and European pump industry for 20+ years and would like to contribute, but don't find it easy to navigate through wiki, and I wouldn't want to a public fight over the rights and wrongs if some one disagrees with me. So if some one wants to help me contribute I would be very happy to do so. I can be contacted at webmaster (@) tlp4u (.) info —Preceding unsigned comment added by Pdeitch (talk • contribs) 20:54, 19 January 2009 (UTC)
OK this is my re-write/comments on the article: sorry if this is not the right way to do it, but it was easier for me to do it in-line. Happy to discuss any points though if some one is interested.
- Thanks for your contribution! OK, first some tips for WP discussion editing: use colons to indent your replies like I have done here. Use four tildes ~ ~ ~ ~ (all together) to sign your "posts". (By the way, I think WP discussions suck but ...)Aaron Lawrence (talk) 11:09, 12 February 2009 (UTC)
- Secondly, hm. You've got quite a bit of useful information to add here, but if you want to edit the whole article I think it would be better if you learned to edit the article yourself. I was expecting you to indicate some areas to add or change ... Editing is not that hard - just click edit this page and change the text you see, keeping the special characters. Anyway, will try to integrate your changes later ...Aaron Lawrence (talk) 11:09, 12 February 2009 (UTC)
- OK, I will go through this bit by bit and move sections to the article. OK? Aaron Lawrence (talk) 13:20, 16 February 2009 (UTC)
[...]and secondly, the mechanical section which in a ‘self contained’ unit has an electric motor, pumping unit, meters, pulsers and valves to physically pump and control the fuel flow.
[...]In general submersible solutions in Europe are installed in hotter countries, where suction pumps may have problems overcoming cavitation with warm fuels or when the distance from tank to pump is longer than a suction pump can manage.
[...] In addition in some markets petroleum is sold with a percentage of oil mixed in. Technically this is dosing because of the relatively small percentage of oil, but is known as a ‘mix’ pump.
- How does this differ from the from the sentence already stating "Typical usages are to add oil to petrol for two-stroke motorcycles"? I added a note about "mix pumps".Aaron Lawrence (talk) 13:20, 16 February 2009 (UTC)
One of the most important functions for the pump is to accurately measure the amount of fuel pumped. Flow measurement is typically done by a multiple cylinder and piston positive displacement meter working on a similar principle to the piston in a combustion engine. The lastest metering technology in use for petroleum is screw metering which provides relatively low wear and tear so that the meter stays calibrated for a longer period. In addition for CNG and Hydrogen coriolis metering is used, but this technology is too expensive for conventional fuels. Not for publication comment- the turbine meter is currently dead for retail applications turbine in the fuel flow. In older gas pumps, the turbine is physically coupled to reeled meters (moving wheels with numbers on the side), while newer pumps turn the turbine's movement into electrical pulses using a rotary encoder. In very old pumps the meter is physically coupled to geared wheels with the price and value numbers on them. As the meter turns, the value wheels rotate to indicate the value of the transaction very much like a large gearbox.
The metrology of gasoline
Gasoline is difficult to sell in a fair and consistent manner by volumetric units. It expands and contracts significantly as its temperature changes. A comparison of the Coefficient of thermal expansion for gasoline and water indicates that gasoline changes at about 4.5 times the rate of water.
In the United States, the National Institute of Standards and Technology (NIST) specifies the accuracy of the measurements in Handbook 44. Table 3.30 specifies the accuracy at 0.3% meaning that a ten gallon purchase could vary between 9.97 and 10.03 actual gallons at the delivery temperature of the gasoline.
The reference temperature for gasoline volume measurement is 60 degrees Fahrenheit or the slightly different 15 degrees Celsius where the metric system prevails. Ten gallons of gasoline at 60F expands to about 10.15 gallons at 85F and contracts to about 9.83 gallons at 30F. Each of the three volumes represents the same theoretical amount of energy. In one sense, ten gallons of gasoline purchased at 30F is about 3.2% more potential energy than ten gallons purchased at 85F. Most gasoline is stored in tanks underneath the filling station. Modern tanks are non-metallic and sealed to stop leaks. Some have double walls or other structures that provide inadvertent thermal insulation while pursuing the main goal of keeping gasoline out of the soil around the tank. The net result is that while the air temperature can easily vary between 30F and 85F, the gasoline in the insulated tank changes temperature much more slowly.
Temperature compensation is common at the wholesale transaction level in the United States and most other countries. At the retail consumer level, Canada has converted to automatic temperature compensation and the United States has not. Where automatic temperature compensation is used, it can add up to 0.2% of uncertainty for mechanical-based compensation and 0.1% for electronic compensation, per Handbook 44.
There are many fewer retail outlets for gasoline in the United States today then there were in 1980. Larger outlets sell gasoline rapidly, as much as 30,000 gallons in a single day, even in remote places. Most finished product gasoline is delivered in 8 to 16 thousand gallon tank trucks so two deliveries in a 24 hour period is common. The belief is that the gasoline is spends so little time in the retail sales system that its temperature at the point of sale does not vary significantly from winter to summer or by region. Canada has lower overall population densities and geographically larger gasoline distribution systems, compared to the United States. Temperature compensation at the retail level improves the fairness under those conditions.
Higher energy prices have raised awareness of this issue for consumers. At the same time, alternative fuel applications are now reaching the retail market and accurate comparisons between them in normal usage are needed. Eventually the basis for retail sales will change from volume units in liters or gallons to energy units such as the BTU, joule, therm or kWh so that electricity, liquids, liquefied gases and compressed gases can all be sold and taxed uniformly.
As far as I know there is no proposed legislation anywhere in the world to move to petroleum fuel sale by energy units therefore I consider this sentence above totally wrong. In addition as far as I know currently all bio fuels, and cng, and lpg do not have consistent calorific values from load to load so unless the dispenser can sense this (not cost effective today), the consumer is not better off. .
The technology for communicating with gas pumps from a point of sale or other controller varies widely, involving a variety of hardware (RS-485, RS-422, current loop, and others) and proprietary software protocols. Traditionally these variations gave pump manufacturers a natural tie-in for their own point-of-sale systems, since only they understood the protocols. 
An effort to standardize this in the 1990s resulted in the International Forecourt Standards Forum, which has had considerable success in Europe, but has less presence elsewhere. ("Forecourt" refers to the land area on which the fuel dispensers are located.)
Autocut in fuel dispenser
Most modern pumps have an auto cut-off feature that stops the flow of fuel once the tank is full. This is done by having a second tube, the sensing tube, that runs from just inside the mouth of the nozzle up to a Venturi pump in the pump handle. While the tank is being filled, air displaced from the tank is drawn up this tube. Once the fuel level reaches the mouth of the sensing tube, air is no longer drawn up the sensing line. A mechanical valve in the pump handle detects this change of pressure and closes, preventing the flow of fuel. 
Where legally required a modern fuel pump will contain Stage 2 control equipment for the vapor recovery system, which prevents gasoline vapor from escaping to the air. The vapour recovered from the vehicle tank is stored in the free space of the underground fuel tank and then purged back to the delivery tanker when the fuel is dropped (Stage 1 vapour recovery).
Several countries in Europe now require the performance of the vapour recovery system to be separately monitored and the pump shut down if the recovery system fails.
Other options seen on fuel dispensers are payment card readers, and cash acceptors.
Regulations This section does not cite any references or sources. Please help improve this section by adding citations to reliable sources. Unverifiable material may be challenged and removed. (July 2008)
Since fuel dispensers are the focal point of distributing fuel to the general public, and fuel is a hazardous substance, they are subject to stringent requirements regarding safety, accuracy and security. The exact details differ between countries and can depend to some extent on politics.
For example in countries fighting corruption, such as Mexico, gas pumps may be more stringently monitored by government officials, in order to detect attempts to defraud customers. In Poland pumps are required to have transaction audit printers inside which becomes the basis of the calculation of the taxes due.
Typically, individual pumps must be certified for operation after installation by a government weights and measures inspector, who tests that the pump displays the same amount that it dispenses. In Europe the MID factory certification option applies to all EU countries and the dispenser can be delivered, installed and selling fuel without local weights and measures intervention, unless the unit is modified or has its calibration changed. It will then be subject to the period inspections which differ in frequency from country to country. —Preceding unsigned comment added by Pdeitch (talk • contribs) 15:32, 26 January 2009 (UTC) sadly it looks like my strikethroughs were ignored by the editor and some of it doesn't read like i wrote it! sorry again. —Preceding unsigned comment added by Pdeitch (talk • contribs) 15:36, 26 January 2009 (UTC)
"Eventual change" of units for retail sales
This article currently says:
- Higher energy prices have raised awareness of this issue for consumers. At the same time, alternative fuel applications are now reaching the retail market and accurate comparisons between them in normal usage are needed. Eventually the basis for retail sales will change from volume units in liters or gallons to energy units such as the BTU, joule, therm, or kWh so that electricity, liquids, liquefied gases and compressed gases can all be sold and taxed uniformly.
While I don't disagree with the logic that metering fuels in energy units would be saner for the consumer, this is the first I have seen anyone seriously suggest that the industry would make such a change or government will mandate a tax as such, but "eventually" is a pretty good weasel word too. Furthermore, I routinely tell people to buy their gas in the morning and very few people actually understand that there is more value-for-money by buying it in the morning, so I find the statement that higher energy prices have raised awareness to be suspect as well. From my perspective, this whole paragraph is in need of revision or removal to meet WP standards. Scott Dial (talk) 15:50, 1 July 2011 (UTC)
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