When the piston is at top dead center, what is the position of the valves?

When the piston is at top dead center (TDC), it is at its highest point in the cylinder, and the compression cycle is typically occurring in internal combustion engines. At this position, the valves play a critical role in managing the air-fuel mixture entering the cylinder and the exhaust gases leaving it.

At TDC, both the suction (intake) valve and the discharge (exhaust) valve are closed to ensure no gases escape and to maintain the pressure needed for the compression stroke. This closure allows for effective compression of the air-fuel mixture in preparation for ignition and combustion. If either valve were open at this point, it could lead to loss of pressure and inefficient engine operation.

In summary, during the top dead center position, having both the suction and discharge valves closed is essential for the integrity and efficiency of the compression process in an engine.