Exhaust valve actuator saftey valve function and what happens spring air pressure is too low

The reason for the introduction of this extra precaution is the recognition of the damage that may occur if the air spring pressure to close the exhaust valve becomes too low at high engine loads. The exhaust valve spindle may then reach the mechanical end-stop in the fully open position while, at the same time, the exhaust valve actuator produces max. hydraulic pressure. The slow-down function in
connection with the safety relief valve will prevent major damage to the camshaft and the exhaust valve. safety valve set point is 21bar. when the air spring pressure to close the exhaust valves had become too low, due to operational reasons, and the valve spindles reached the mechanical end-stop in the fully open position while, at the same time, the exhaust actuator produced max. hydraulic pressure. This led to the cams slipping from their positions and to the exhaust valve air pistons becoming damaged. when the piston reaches the mechanical stop there wont be any air under piston and all spaces are filled with oil which is not compressible resulting in cam slippage.