Is it necessary to break the vacuum immediately after an emergency shutdown of a condensing steam turbine?
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Question: After an emergency shutdown of a condensing steam turbine, is it necessary to stop the steam seal immediately, thereby breaking the vacuum?
There is no need to break the vacuum, and it cannot be done through the steam from the shaft seal; doing so could allow cold air to enter the machine rapidly through the shaft seal and strike the impeller, which is in a high-temperature state, causing damage； Just stop the vacuuming, and the pressure will rise naturally ； If rapid vacuum breaking is required, it is recommended to stop the condensate pump; the vacuum can then be broken through the atmospheric safety valve ；
The turbine must be rotated after it stops, so it’s fine for the air seal to keep running. There’s no need to break the vacuum immediately either
Since an emergency shutdown has already been initiated, why break the vacuum? It is appropriate to break the vacuum during an emergency shutdown; be sure to wait until the vacuum level drops to zero before stopping the steam supply to the shaft seal
One cannot first stop the steam seal before breaking the vacuum; if vacuum pumping continues after the steam seal is stopped, cold air will enter the turbine along the shaft end, causing a significant temperature drop that may lead to rotor bending.
Breaking the vacuum is done to achieve rapid stopping; typically, air compressors are equipped with vacuum-breaking valves that open automatically to enable quick stopping. Centrifuges also stop quickly when they do so under load, so there is no need for this process