Regarding the question of whether towers are considered pressure vessels? ? Urgent! Urgent! Urgent! !

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1. Resin towers and filters are commonly used in wastewater treatment. Sometimes, the water in the resin tower does not fill it completely; that is, there is a gas phase above the water level at the beginning. If it is assumed that the gas phase initially contains only the saturated vapor pressure of the liquid (absolute pressure, with constant temperature and assuming no connection to the atmosphere), then as the water level rises and the volume of the gas phase decreases, will the pressure in the gas phase increase? In other words, normally a decrease in the volume of the gas phase leads to an increase in pressure, but will this increased pressure push the vapor back into the gas phase? In other words, does the pressure in the gas phase remain unchanged as the liquid level rises? ? 2. If the gas phase above the liquid level in the resin tower is in communication with the atmosphere, then the valve connecting it to the atmosphere should be closed during operation. When water is fed in for filtering, the volume of the gas phase at the top decreases, and as a result the pressure in that gas phase space may exceed 0.1 MPA. Should this be considered sufficient to classify the filter as a pressure vessel? ? ? ? The manufacturer says that the filter does not belong to pressure vessels. . . . . Confusion. I hope the expert can give some guidance! !