Can a metal tube float flow meter be used under negative pressure?
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As the title suggests, I have been working on an experiment recently to determine the pumping speed of a set of vacuum units. However, problems arose with the flow meter; during attempts to adjust the flow rate, it was observed that the pointer of the metal tube float type flow meter vibrated violently and unstably, making it impossible to obtain a reading. Is it because metal tube float flow meters are not suitable for negative pressure conditions? I would be extremely grateful if a senior who knows the answer could let me know!
When the inlet air pressure is below standard atmospheric pressure, the indicated value is always higher than the actual measured flow rate; the extent of this overestimate depends on the degree to which the valve is open (or, in other words, on the magnitude of the resistance in the gas path), which determines the level of negative pressure generated during suction. The smaller the valve is closed, the greater the negative suction pressure generated, and the higher the proportion becomes.
Teacher, have you solved this problem? I have also been researching the advantages and disadvantages of the positive and negative pressure measurement methods for metal rotor flowmeters. I am not quite sure as to why these methods are not suitable for measuring negative pressure using pumps; I would appreciate your advice