What is the change in the instrument reading compared to the actual value when a orifice plate flow meter is installed in reverse?
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We have an exam question. Here is the question. In newly installed devices, the orifice plate is sometimes installed in the wrong direction. What changes occur when the orifice plate is installed incorrectly compared to the actual value? Please draw a schematic diagram to illustrate it. Draw the changes in positive and negative static pressure when the orifice plate is installed reversely. May I ask the experts how to draw pictures? . . Urgent Urgent Urgent
When the orifice plate is installed reversely, with the flared end facing the fluid, the pressure difference across the orifice plate decreases, resulting in a flow rate indication that is lower than the actual flow rate.
The flare of the orifice plate should normally face forward; if it faces backward, it can cause flow deviations. This is likely related to the location of the pressure measurement point on the orifice plate. The pressure at the positive pressure port should have no effect, while the pressure measured at the negative pressure port will definitely be affected. It is likely that the lowest pressure point measured under negative pressure has shifted backward, resulting in an increase in the pressure at that measurement point; this leads to a smaller differential pressure being measured, and thus a lower flow rate is indicated.
The original poster can take a look at the relevant posts on this issue. http://bbs.hcbbs.com/thread-1568026-1-1.html
Under normal conditions, as the fluid flows through the orifice plate, it encounters resistance; as a result, the local pressure near the front surface of the orifice plate increases. Near the back surface of the orifice plate, the fluid contracts, causing its flow velocity to increase, its kinetic energy to rise, and its potential energy to decrease, thereby lowering the static pressure. The orifice plate creates a differential pressure, and the flow rate is determined based on the proportionality between this differential pressure and the flow rate itself. If the orifice plate is installed in the reverse direction, on the one hand, the flow velocity increases due to the guiding effect of the inlet slope, resulting in a greater pressure difference; on the other hand, since the inlet is not at a right angle, the resistance decreases and the flow coefficient increases. As a result, at the same flow rate, the pressure difference decreases, and consequently the output of the gauge is reduced.