Is the pressure at the inlet of the air compressor positive or negative?
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As is well known, the suction inlet of a compressor has a certain degree of suction force; so is the pressure at its inlet positive or negative? For some compressors, control is achieved through the inlet pressure difference and outlet pressure at the first stage, while for others it is controlled using the pressure difference at the last stage and the outlet flow rate. I’d like to ask everyone: the inlet at stage 1 is under negative pressure, right? The inlet at the final stage should be under positive pressure, then? For another example, what is the pressure condition at the two pressure tapping points corresponding to the inlet pressure difference? When comparing the pressures at the two pressure tapping points at the inlet, is the pressure closer to the suction inlet lower or higher than the pressure further away from the suction inlet? In other words, are the positions corresponding to the positive and negative pressure sampling points of the pressure transmitter fixed?
Just understand one thing: in the absence of external work, gases always flow from high pressure to low pressure! If what enters the compressor is atmospheric air, which has no pressure, then there must be negative pressure at the inlet; otherwise, how can air get in?
Gas flow requires a pressure difference, so there must be a pressure difference at both ends of the intake pipe. Where there is flow, there is pressure loss; therefore, there is also pressure loss at both ends of the intake pipe. As for how large this pressure loss is, and whether it should be ignored, that’s another matter
Why can the inlet be at positive pressure? Who does the work on it? Personally, I think it should be negative pressure.
What he is asking about is the situation of multiple levels of compression. The first stage is definitely under negative pressure, but as for the transition from the second stage to the first stage, is it the second stage that blows air towards the first stage, or is it the first stage that draws in air from the second stage?