There are many different types of valves that can be used for the aircraft engine. While they each have different physical characteristics and serve different purposes, the aircraft valves tend to operate in a similar fashion. For example, the valves in the cylinders of an aircraft engine must endure severe conditions, including high temperatures, corrosion, and operating stresses. For this reason, metal alloy is often used in most valves so that they can resist and withstand being subject to extreme factors. However, some valves, such as intake valves, must function at temperatures lower than exhaust valves, and can thus be made of chromium-nickel steel. On the other hand, exhaust valves can be built of nichrome, silchrome, or cobalt-chromium steel because these materials are much more heat resistant. For more information on the different aircraft valve types, see below for more information.