About existing valve gear solutions
Recent status: Several disadvantages, especially for large valve piston travel required now
The best known valve gears show different disadvantages that cannot be fully avoided. Depending on the preferred application of a steam locomotive, one or another valve gear was applied.
Today, efficiency is more important than before, and large valve piston travels are needed to achieve this.
The most common type was Walschaerts valve gear. This type, from today's point of view, has a big disadvantage by using an open loop for the expansion link, concerning lubrication (as an environmental impact) and wear (as a maintenance cost related impact). A deviation of that, the Helmholtz valve gear, would only reduce the maintenance cost related impact by making rework of the expansion loop easier.
The second most common type was Baker valve gear. This type has a big disadvantage at large valve piston travels, giving unequal valve event results.
The Southern valve gear even was proposed by L.D. Porta, but still has a big disadvantage, meaning vertical movement of the driver suspension resulting in varying valve events.
Other valve gears could not make a breakthrough because of other disadvantages, let it be bad valve events or expensive production or maintenance.
To avoid these disadvantages, a new version of valve gear was designed.
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