When you visit a large motorsport trade show, as I recently did, there will be a number of engine component suppliers present, some of which will be selling high-quality valvetrain components. In the display cabinets ranged before you, among other things you are likely to see valves of all sizes, shapes and materials, there for you to examine and discuss with the various specialists manning the stands.

Among these exhibits, there is sometimes a single, horribly distorted part, proudly displayed. What possible use can this be? One of the primary requirements for a valve to operate in a satisfactory manner is for it to be very straight. Straightness tolerances are measured in microns over the length of the valve, yet these specimens are severely twisted.

The reason a valve manufacturer or supplier wants you to see the twisted valve is to prove to you that their valves are possessed of a large measure of ductility - in other words, the valve will behave plastically beyond yield. This is of little consequence in normal operation, but can be a real saviour in the event that the unexpected happens.

There are many reasons why a valve might see loads that are far different in terms of magnitude and direction from those we can expect in normal service. Normal operating loads come from the valve(Safety valves ) being opened (stem compression) and closing - tension in the stem and seating loads, which may be compressive, tensile or bending depending on the location in the component. There are also some loads due to friction in the valve stem. However, none of these require a large degree of ductility.

When something goes really wrong - for example, the inlet swallowing something it shouldn

2011-02-24

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