this valve used in the refinery.
This is a 'Trip and Throttle' (T T) valve that is maintained in a 'Fully Open' postion during normal turbine operation. It is maintained open by a Hydraulic Control system that, should any of many shutdown conditions occur, the hydraulic oil will be dumped to its reservoir by the operation of a Solenoid valve, actuated by the shutdown signal, and the T T valve will immediately close, stopping the steam flow to the turbine speed control steam chest in a safe manner. The valve handwheel is then operated to ensure that the valve remains fully closed until the system is ready for re-start. The valve cannot be opened again until the shutdown condition has been rectified and the hydraulic system reset to restore the oil pressure to the valve. The valve however, can then only be re-opened manually and slowly until the turbine is brought to the 'Minimum Speed Control' Governor setting. When settled down at this condition and the steam chest valves are under the control of the Governor, the T T valve is swung wide open. This latches the valve in the fully open position until another shut down occurs,
