The valve lead and valve seat work under most demanding conditions. These must remain tight when the valve is seated. When the exhaust valve just starts to open the gases at high pressure and temperature escape at great velocity that may cause erosion of the valve and seat material. Such erosion also take place if some dirt or grit from ash gets lodged between the valve and seat and there is leakage of gas.
If the fuel contains elements such as sodium and vanadium, at high temp a viscous and sticky compound is deposited that is very corrosive. At low temperature there may be dew formation and sulphur oxides produce during combustion coming in contact with water may form acid causing corrosion of parts.
The valve seat therefore require periodic servicing. If the seat were an integral part of exhaust valve cage or the cylinder cover, then the entire cage or cover may need to be replaced, which would be very expensive. For this reason detachable valve seats made of high quality heat resistant material is fitted.
Valve Seats main functions:
- Compression gas sealing – Prevents compressed gaseous bodies and combustion gas from leaking into the manifold.
- Heat transfer – Releases heat in the valve to the cylinder head
- Strength – Holds tight when the valve is mounted.
- Wear-resistance – Hard to wear down under high heat and high load.
Properties of molybdenumMolybdenum is hard slivery metal with very high melting point. It is primarily use to make alloys with other metals. The most common alloy of molybdenum are those with steel. Molybdenum improve strength, toughness, resistance to wear and corrosion and ability to harden steel.