Suppose a differential pressure transmitter is used to measure the pressure dropped across a baghouse, an assembly using multiple fabric “socks” to filter particulate material from a gas stream, like a large-scale vacuum cleaner.
Gas passes through the socks, filtering out the particulate matter. The DP transmitter’s pressure measurement serves to indicate how clogged the socks are:
When the transmitter signal reaches a certain value (indicating clogged filter socks), a control system triggers either a mechanical shaker or a blast of gas from jets located near each sock shakes the dust from the outside area of each sock, the dust falling down into the narrow area below where it is extracted over time from the baghouse.
Suppose an instrument technician leaves the three valves in the positions shown (hollow = open ; solid = closed). What effect will this have on the socks over time as they perform their filtering job, assuming the control system continues to operate as designed?
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With the Inlet valve of HP side & LP side of the DP transmitter closed (solid), the transmitter will not be able to sense the pressure difference across the socks.
Moreover with the equalising valve OPEN ( Hollow), the pressure input at the HP and LP side of the DP transmitter will be equal and hence the DP transmitter will show a value 0 mmWC