They decide how much fresh gas mixture can reach the combustion chamber. They control when the combusted mixture is expelled.They have to keep a tight seal – and this consistently. And they have to work reliably as long as the engine is running. In short: Valves have to perform a tough job.
After all, the valve heads with their sealing surfaces hit the valve seats up to 70 times per second. The inertia forces and the forces from the valve springs and combustion pressure represent a great challenge for the components. Especially the exhaust valves, which are heated up considerably by the exhaust gases with temperatures up to 800 °C. In the short time during which the sealing surfaces are in contact, as much heat as possible must be transferred from the valve seat to the cylinder head. However, not only the heat of the exhaust gases is attacking the valves, but also the aggressive chemical components, which can cause deposits and corrosion.
It’s up to the material
To ensure that valves in combustion engines work reliably even under extreme conditions, first-class materials have to be used. MAHLE valves are made from high-grade alloyed materials that are matched optimally to the demands. The materials are developed in close cooperation with the engine makers.
 | Depending on the demands, different materials may be combined to make use of the positive properties of each material and to provide the optimum support for the different areas of the valve. For example, in a MAHLE bimetal valve, the valve head is made from highly alloyed steel, which is connected with the valve shaft in a way that is resistant to chemical and thermal attack. The actual valve shafts have to be hardened and of high strength. |
According to demands, MAHLE valves are optimised further to reduce wear and increase service life. This may be achieved by hardening the valve seat or by build-up welding with special alloys (stellite) to hard-face the sealing surface. The valve shafts are often nitrided or chromeplated to improve their sliding and wear properties.
Keep cool with liquid metal
A special highlight for engines under extreme thermal loads is the sodium filled hollow bore valve. This type of MAHLE valve has a deep bore that reaches from the valve head into the valve shaft. The bore is filled two thirds with sodium and closed afterwards. When the engine is operating, the sodium becomes liquid and turns into an excellent heat conductor. Due to the up and down movements, the heat is transported from the valve head to the valve shaft by the liquid sodium, where the heat is dissipated via the valve guide to the cylinder head and subsequently to the coolant circuit.
At a glance: The sodium filled hollow valve
MAHLE valves – news from the production lines
MAHLE is the world leader in the serial production of sodium filled hollow bore valves and manufactures valves with shaft lengths from 80 to 210 mm on state-of-the-art flexible manufacturing facilities. Flexible technologies ensure high quality standards and allow economical production of even small batch sizes. Also our customers in the aftermarket benefit from our close cooperation with the international automotive industry. We can offer a comprehensive valve program for car and truck engines, which has now been extended by more than 400 types.
 | In addition to a significant widening of the valve range for vehicles from Audi, BMW, Citroën, Ford, Opel, Peugeot, Renault, VW and Volvo, especially the program for Italian manufacturers such as Alfa, Fiat and Lancia has been expanded considerably. Also in the commercial vehicle sector (Deutz, MWM, Perkins, etc.), we have added to our range. |
The latest additions to our program can be found in our current Valve Catalogue 2005, which can be ordered from your wholesaler.