Pressure Transmitter Fault Pressure Analysis

- Mar 14, 2018 -

1. The device pressure is too high, the interlock does not act, and the vent valve does not act to stop. Failure Analysis: Under normal circumstances, when the pressure is too high, the PLC internal contact is turned on, send a signal to drive the four-way 24VDC solenoid valve action, vent valve action. In this passage, the pressure is extremely high and there are three possible conditions for the vent valve not to act:

1 PLC internal contacts, terminal faults;

2 relay, loop connection failure;

3 solenoid valve failure.

Fault handling: When the field measurement pressure is high, an electrical signal is sent out to indicate that the pressure controller on the site is not faulty. The four-way type 24VDC solenoid valve has an electrical signal, no air source output, and the vent valve does not operate. After the process bypass control, check the solenoid valve controller and check the contact terminals. The contact is found to be in poor contact and recalibrated after processing. After several trials, it was completely easy to use, matched with the car and put on an interlock.

2. Heavy oil manifold pressure alarm interlock system, due to boiler fuel oil heavy oil header pressure drop, and the standby pump can not be automatically started, resulting in heavy oil pressure continues to drop until the boiler chain action cut off heavy oil and stop, causing failure.

Failure inspection, analysis: Under normal circumstances, when the pressure of the heavy oil header drops to a certain value, the spare pump should be started automatically so that the heavy oil maintains a certain flow and pressure. Now that the standby pump has failed to start, it means that the standby pump has not received a pressure drop signal, which means that the pressure transmitter of this system does not feel the change of the main pressure. The reason for the inspection was that the spacer fluid in the catheter was discharged and the heavy oil entered the pressure guiding tube and the positive pressure chamber cavity of the transmitter. Due to the use of spacer fluid to measure the main pipe pressure, the pressure guiding pipe and the instrument do not use heat tracing, and the solidification point of the heavy oil is relatively low. Therefore, condensation occurs in the pressure guiding pipe and the membrane chamber, and the change in the main pipe pressure cannot be sensed and transmitted. At the same time, due to the volume expansion of the heavy oil, the sensor element is indicated by a high force, and this value is always maintained. When the header pressure drops, this value does not change and the backup pump does not start until a shutdown occurs.

Troubleshooting: Use a steam purge to guide the pressure tube and remove the meter membrane chamber for cleaning with gasoline. After the instrument is re-used, the instrument must be subjected to static pressure test and inspection, and the pressure-relief tube should be refilled with spacer fluid.

3. The device pressure switch malfunctions, causing an interlocking action.

Failure inspection, analysis: There are two reasons for the analysis: the pressure tube is clogged or leaking, and the pressure switch is faulty. After inspection, it is found that impurities exist in the pressure switch pressure guiding tube, which can cause pressure switch action. In routine maintenance, the pressure switch pressure tube must be cleaned and treated frequently.

Troubleshooting: After cleaning dirt, it will return to normal.

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