In the event of leaks in fuel tanks, not only can fuel leak itself, but also environmentally harmful fuel vapors can get into the air. Experts estimate that such undesired evaporations due to leakages are still responsible for up to 20% of all hydrocarbon emissions from cars worldwide. It is therefore important to identify leaks in the tank at an early stage and have them rectified. The tightness of the tank is checked primarily by pressure pumps. They are installed in the tank and generate an overpressure for a brief moment at regular intervals. If this pressure drops, the sensors of the device report a leak.
Tank leakage pumps are an effective means to early detect even smallest leaks in order to avoid damages to the environment. As a result, the pumps are gradually establishing themselves as the standard for cars with conventional drives.
Werner Müller, Head of Mechanical Solutions at SGL Carbon.
After the mandatory installation in North America, the tank leakage pumps with the introduction of the new emission standards China 6a-c have gradually become mandatory in China since this year.
For this purpose, SGL Carbon has been supplying tailor-made components made of a special graphite-plastic mixture to an internationally operating renowned automobile manufacturer for their pump system, diagnostic module for tank leaks. The system was originally developed in the late 1990s but is in greater demand than ever due to the even stricter emission standards. A corresponding multi-year framework agreement ensures cooperation for the coming years.
The particularly complex thermoset-graphite components, which are only a few centimeters in size, are the heart of the so-called vane-type pump. The pump is named like this because small movable blades, so-called vanes in the rotor, compress the air by rapidly rotating it in cells that are getting smaller and smaller, thus generating air pressure. The material of the vanes and rotor must therefore have a particularly high mechanical strength combined with very good sliding properties.
“The graphite-based material is particularly suitable for these pump components because it has exactly these properties. In addition, the material is chemically resistant to gasoline vapors and has excellent dry-running properties, ”explains Werner Müller, Head of the Mechanical Solutions product segment at SGL Carbon, which manufactures the automotive components from thermoset graphite. As a result, graphite components enable particularly reliable and long-lasting operation of the pumps. Another advantage of thermoset graphite is the low weight, which has a positive effect on the CO2 balance.
The small but particularly complex components for the leakage pumps are manufactured at the SGL Carbon location in Bonn. In addition, many other graphite components for the automotive industry, such as bearings and seals made from special graphite, as well as solutions for other industries, such as the growth sectors LED and semiconductors, are also manufactured here.
Tank leakage pumps mostly consist of a small air pump with graphite components inside (see similar application in picture on the left), based on the vane principle with a 12-volt electric motor and a solenoid-operated switching valve with a reference opening. At some point after the engine is switched off, the pump turns on and blows air through a reference opening while the control unit measures the power consumption of the engine. If the current measurement does not at least equal the reference measurement, the control unit will interpret this as a small leak in the tank system and display the corresponding error codes in the cockpit with indicator lights. A way to the workshop becomes inevitable.