Fuel dispenser

A gas pump (or fuel pump ) is a device at a gas station, is filled with the fuel ( eg, gasoline, diesel, natural gas, hydrogen, LPG ​​, occasionally also an additive such as AdBlue ) into the to be refueled vehicle. The dispensing valve - known colloquially nozzle - is connected via a hose to the pump. About the dispensing valve, the fuel is filled into the tank of the land, water or air vehicle.

Temporal development

The first taps on public property were in the 1920s, often on sidewalks in front of inns or department stores. They had hand-operated petrol pumps, also known as the " Iron Maiden ". To refuel you knocked on the associated business and was operated. In the first models was just pumped. With advent of the glass cylinder outside the tapped fuel load was read on a scale, which then ran into the tank. In the two versions of glass then has already been pumped, while the other container contents proceeded in the tank. From the mid- 1930s there was first pumps that had counters with price display.

Until the late 1970s, only columns were used with a mechanical calculator. 1978, the first electronic price calculator for pumps in Germany was developed, then gradually disappeared after the gas pumps with mechanical counters at gas stations and were replaced by electronic ones. Likewise, most gas pumps, where with two hoses up to two different products could be fueled, now by so-called MPDs ( acronym for Multiple Product Dispenser) were replaced. These pumps up to five different fuels can be submitted per Pump side. In addition, there are many gas stations high performance fuel pumps that are specially designed for the refueling truck. Since they have a capacity of up to 130 l / min (against about 35 l / min at car columns), they are equipped with tapping valves, which have a much larger diameter than car nozzles. This serves on the one hand the faster promotion, on the other hand they may be confused with severe car - tapping valves because they do not fit in car filler neck. In the period of transition from leaded to unleaded gasoline, the diameter of the nozzles was reduced to prevent erroneous refueling with leaded gasoline. The diameter at petrol pump nozzle is 21 mm and 25 mm for diesel in passenger cars.

A pump also includes a display for volume and price control of the filled fuel. In addition, information on the octane number ( see knock resistance ) and various safety regulations the rule.

In self-service gas stations tank data ( pump number, fueled product, quantity delivered, unit price per liter and has to be paid ) are also transferred to one or more cash in the shop. For several years geldautomaten similar terminals are installed in gas pumps, where you can pay the fuel directly using a credit card.

Pump of 1958 in Traktorium in Drasenhofen

Historical dispensers in the Deutsches Museum (right one " Iron Maiden " )

Old gas pump at a gas station in Vienna

Historic gas pump on the Roscheider Hof bei Konz (1 August 2004)

Petrol pumps in the former Soviet Union

Gas recirculation

Modern automotive petrol stations use pumps and nozzles with a gas recycle to the extraction of volatilized to gas fuel. This health and environmentally hazardous benzene vapors are largely absorbed. In Germany, under the Regulation to limit hydrocarbon emissions during refueling of motor vehicles ( 21 BlmSchV ) since 1 April 2003, the newly built petrol stations provision that the proper function of the gas recirculation is automatically monitored ( vapor recovery monitoring). In case of failure of the gas recirculation, the pump must be set within 72 hours of service, otherwise the further delivery of petrol at this petrol pump through technical measures is automatically suppressed.

Vapour balancing is called the process that for every liter of liquid phase, a liter of gas phase between supplying tankers and (usually :) Erdlagertank the gas station switches back. The vapor pressure of gasoline at 20 ° C to 60 kPa ( 0.6 bar), the ratio of density of liquid = 750 g / l density gas phase = 4.5 g / l can be carried back line of fuel vapor at each filling step calculation avoid 0.6 % fuel loss.

Measuring the flow rate

The measurement of the flow rate inside the pump is effected by so-called helical or reciprocating knife. The by a suction pump ( inside the pump ) or pressure pump (outside the pump ) induced flow pressure moves 2-4 piston in the piston diameter or the counter-rotating micrometer, driving a common shaft. Thus, the rotation of the shaft is a measure of the flow rate. To this shaft, either a mechanical or electronic unit is flange-mounted, an electronic pulse generator ( in modern fuel dispensers ), which converts the rotary motion of the shaft into countable pulses to the electronics. The sight glass on the pump point allows the user to control whether only fuel ( and no air ) passes through the flow meter. The permitted in commercial traffic tolerance ( calibration error limit and error limit ) is uniformly throughout the EU / - 0.5 %, ie in a display of 100 liters from 99.5 to 100.5 liters must have been submitted. At public filling stations the discharge amount of the fuel is monitored by the Bureau of Standards. There are to every two years inspections of quality and delivery quantity ( Metrological check ) performed. For initial verification, re-calibrations and recalibrations after previous repair basically done a full examination, in accordance with Directive 2004/22/EC ( MID) placed on the market columns or the measuring instruments contained shall apply as from the factory as erstgeeicht.

Temperature compensation

Since the implementation of the European Directive MID dispensers are permitted with temperature compensation in Germany. These same during the filling process to the displayed delivery amount corresponding to the calculated expansion with an assumed ambient temperature of 15 ° C. In our latitudes, the ground temperature all year is rarely above 15 ° C so that temperature compensation usually higher than the actual tax amount shown and will be charged. The correction factor at motor gasoline approximately one per thousand per Kelvin, and it follows that, for example, at a discharge of 100 liters 9 ° C cold fuel 100.6 liters would be settled. Temperature-compensated pumps are thereby seen that on bezel and bill the unit for the discharge amount is not " liter " or "l " is, but " liters at 15 ° C". For the operator of temperature-compensated pumps have the advantage that the delivery to the customer to the same conditions as well as the supply (This is basically temperature-compensated ), which the otherwise inevitably occur " loss " is reduced. For the customer, temperature-compensated pumps have the disadvantage that these be measured in comparison to a conventional, in the actual discharge temperature, column give off less fuel.

Nozzle automatic

By tapping valve Automatic ( ZVA ) of the refueling process is terminated automatically when tank is full, the operation is as follows:

The flow of fuel generated in the small gap at the valve seat a pressure ( Venturi effect). Through the antenna line, which leads via the diaphragm and the ball -and-tilt safety shutter for sensing port, air is sucked in to compensate for the negative pressure. As long as the sensing port is free, the nozzle can work. When fuel reaches the sensing end of the pipe, the air supply is interrupted. Immediately, a negative pressure builds up, the diaphragm is sucked up and triggered the shutdown. Because the valve it closes against flow direction, the back pressure softens the sidings shock and there is no high pressure peak. The automatic cut-out is also actuated when the sensor cable is sealed by the ball of the safety trigger. This happens whenever the dispensing tube is directed upwards; For example, if it is not correct during the filling downward when it from slipping out of the filler, or when the shift lever is accidentally operated during removal from the pump.

Water protection and explosion protection

The filling area around the fuel dispensers is designed to protect against spills, liquid-tight seeps into the ground water polluting substances, eg precast concrete with special permanently elastic grouting. On the edge of the area consist upstands to prevent spilled fuel can flow from this area. This filling area is drained by the separator, even when the surface is covered. The pumps themselves are so situated that they can not be damaged easily by shunting vehicles ( collision ), eg by increased Anfahrborde or circumferential protection gangs. To prevent dangerous electrostatic discharge ( arcing ), the nozzle on the pump hose is grounded; also the roadbed of the fueling area with highly flammable products (gasoline) to a certain extent must be electrically conductive to allow a potential equalization between tap fittings and vehicle. When aircraft refueling before the actual filling process until a conductive connection is made to the gas pump by clamping one attached to the pump ground wire to the ground connection of the aircraft. These requirements were in Germany until the end of 2012 the technical regulations for flammable liquids - flammable liquids 40 - petrol or flammable liquids 30 - filling stations, emptying points and aircraft refueling points are established and by the TRBS 3151 - the prevention of fire, explosion and pressure hazards at gas stations and filling stations replaced for filling of land vehicles, which summarize the relevant requirements for storage and bottling of mineral oils and liquefied petroleum gas ( LPG ) and natural gas.