Fuel dispenser

A fuel dispenser is a machine at a filling station that is used to pump gasoline, diesel, CNG, CGH2, HCNG, LPG, LH2, ethanol fuel, biofuels like biodiesel, kerosene, or other types of fuel into vehicles. Fuel dispensers are also known as bowsers (in Australia)., petrol pumps (in Commonwealth countries), or gas pumps (in North America).

History

The first gasoline pump was invented and sold by Sylvanus F. Bowser in Fort Wayne, Indiana on September 5, 1885. This pump was not used for automobiles, as they hadn't been invented yet. It was instead used for some kerosene lamps and stoves. He later improved upon the pump by adding safety measures and also by adding a hose to directly dispense fuel into automobiles. For a while, the term bowser was used to refer to a vertical gasoline pump. Although the term is not used anymore in the United States, it still is used sometimes in Australia, New Zealand and Canada.

Many early gasoline pumps had a calibrated glass cylinder on top. The desired quantity of fuel was pumped up into the cylinder as indicated by the calibration. Then the pumping was stopped and the gasoline was let out into the customers tank by gravity. When metering pumps came into use, a small glass globe with a turbine inside replaced the measuring cylinder but assured the customer that gasoline really was flowing into the tank.

Design

A modern fuel dispenser is logically divided into two main parts — an electronic "head" containing an embedded computer to control the action of the pump, drive the pump's displays, and communicate to an indoor sales system; 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 some cases the actual pump may be sealed and immersed inside the fuel tanks on a site, in which case it is known as a submersible pump. 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 modern pumps, the major variations are in the number of hoses or grades they can dispense, the physical shape, and the addition of extra devices such as Pay at the pump devices and attendant "tag" readers.

Historically, fuel dispensers had a very wide range of designs to solve the mechanical problems of mechanical pumping, reliable measurement, safety and aesthetics. This has led to some popularity in collecting antique dispensers, especially in the USA.

Nozzles

Nozzles are attached to the pump via flexible hoses, allowing them to be placed into the vehicle's filling inlet. The hoses are made very tough to survive hardships such as being driven over, and are often attached using heavy duty spring or coil arrangements to provide additional strength.

The nozzles are usually color coded to indicate which grade of fuel they dispense, however the color coding differs between countries or even customers. For example, a black handle is used to warn people that the fuel dispensed is diesel. In the United States, diesel fuel pumps commonly use green hoses and green slipcovers over the nozzle.

Blending

In some countries, pumps are able to mix two grades of fuel together before dispensing; this is referred to as blending or mixing. Typical usages are in a "mix" pump to add oil to petrol for two-stroke motorcycles, to produce an intermediate octane rating from separate high and low octane fuels, or to blend hydrogen and compressed natural gas (HCNG).

Flow measurement

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 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.

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 than 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 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.

In some regions, regular required inspections are conducted to insure the accuracy of fuel dispensers. For example, in the US state of Florida, the Florida Department of Agriculture and Consumer Services conducts regular tests of calibration and fuel quality at individual dispensers. The department also conducts random undercover inspections using specially designed vehicles that can check the accuracy of the dispensers. The department issues correction required notices to stations with pumps found to be inaccurate. Most other US states conduct similar inspections.

Communications components

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.

Other components

A modern fuel pump will often contain control equipment for the vapor recovery system, which prevents gasoline vapor from escaping to the air.

Regulations

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.

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.