Trying to detect when a pneumatic conveying line plugs can be challenging. A line can plug at any moment, usually without notice and typically at the worst time for it to happen. Then begins the expensive and time consuming process of taking the line apart to find and clear the plug.
Some systems use a pressure transducer to detect when the line is starting to plug. When a plug starts, there will be resistance and an increase in line pressure. The blower has to work harder to try and blow the plug free. A rise in convey line pressure occurs and the pressure switch gives an indication. This may be fine for shorter conveying distances but when the distance is great and/or the diameter of the pipe becomes large, the pressure transducer may not react quickly enough. Sometimes pressure oscillations from material feeding into the line can cause erroneous errors. The signal may not offer a stable enough signal to monitor.
The use of a microwave flow/no flow detector can aid with the plugged convey line scenario. Using the Doppler effect, the detector can tell if the normal flow of material is beginning to slow. The best place to locate this device is near or at the end of the convey line. If the line begins to plug, it can detect a lessening flow and go into alarm mode. The flow/no flow detector can be used in conjunction with a pressure transducer to confirm a plugged situation. The flow detector can be tuned to the particular application for sensitivity and alarm delay. In this manner, the operator can use the pressure readings to further determine if a plug condition is starting. Consider the use of a flow/no flow detector as an “umbrella” policy for your conveying lines.
Ross Jamison
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