Regarding the measurement of backflow instruments
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As shown in the figure, this is a schematic diagram of the installation of the catalyst differential pressure gauge; purge lines are connected to both the positive and negative pressure sides of the pressure tap tube. When in use on the positive and negative pressure sides, the purge line is also open. My question is: won’t the pressure of the purge air affect the pressures on the positive and negative sides, thereby affecting the measurement of the differential pressure?
Instrument calibration is carried out with backflow air; theoretically, the pressure measurement remains unaffected as long as the pressure of the backflow air is stable.
It still relies on the purge air from this gauge to transmit pressure
Could you elaborate? As I understand it, P2 is the backflow pressure, while P1 is the actual pressure inside the container; it is P1 – P2 that is the pressure measured by the gauge, and this value is lower than the actual pressure P1 inside the container. Is it to use the zero setting of the pressure gauge in order to subtract the backflow pressure P2?
Could you explain in detail the measurement principle of a backflow pressure gauge?
1. The backflow air should create an open-air blowing effect right at the equipment end, to prevent pressure differences from forming in the measurement pipeline and causing errors. 2. In the case of a differential pressure gauge, counterflow air with the same flow rate is present on both the positive and negative sides, which cancels each other out and eliminates errors. There is 1 main thing to pay attention to.
It can be understood in that way as well, but the backflow pressure should be higher than the pressure inside the container; otherwise, the catalyst will enter the pressure guiding tube and cause blockages. When it gets blocked, the only option is to wait until operations stop before trying to clear it.
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The purge pressure definitely affects the working blowing pressure. During purging, the equilibrium relationship between pneumatic and hydraulic pressures is disrupted, resulting in inaccurate measurements that must be disregarded.
It should be that the backflow pressure is greater than the process pressure. Simply put, it can be calculated as follows: the required pressure difference is P(difference) = P(top) – P(bottom). However, because the pressure tap tubes are blocked, the same purge pressure is applied to both the top and bottom sides; as a result, the pressure difference becomes P(difference) = {P(purge) – P(top)} – {P(purge) – P(bottom)}. After simplifying this equation, we still get P(difference) = P(top) – P(bottom), thus solving the problem of blocked pressure tap tubes
If it’s not measuring differential pressure but rather pressure, then your statement doesn’t apply.