How should a differential pressure alarm on a dust collector be handled

During normal operation, a fabric filter dust collector continuously monitors the pressure difference (differential pressure) between its inlet and outlet. Differential pressure is one of the most critical real-time parameters reflecting the unit's operating status, and a differential pressure alarm is the most common fault signal issued by the system.

When faced with a differential pressure alarm, many plant operators' initial reaction is to "wait and see" or assume the alarm will stop on its own. Such an attitude risks missing the opportunity to address the issue promptly, potentially allowing the problem to escalate.

What is differential pressure, and what is the normal operating range?

Differential pressure refers to the difference between the gas pressure at the dust collector's inlet and outlet, typically measured in Pascals (Pa) or millimeters of water column (mmH2O). The magnitude of the differential pressure reflects the resistance encountered by the gas as it passes through the filter bags: a higher differential pressure indicates a thicker dust accumulation on the bags or greater resistance to gas flow. Consequently, the fan requires more power to overcome this resistance, and the system's actual airflow volume decreases accordingly.

For pulse-jet fabric filter dust collectors, the normal operating differential pressure range is typically between 800 and 1,500 Pa, though the specific range varies depending on the equipment model and operating conditions. Manufacturers provide a recommended control range, with the high-pressure alarm threshold usually set between 1,500 and 2,000 Pa; the alarm triggers when the pressure exceeds this value.

Common Causes of High Differential Pressure Alarms

Cause 1: Malfunction of the dust cleaning system. This is the most common cause. Issues such as damaged pulse valves (failure to actuate or air leakage), insufficient air reservoir pressure, pulse controller malfunctions, or blockages in the compressed air lines can impair cleaning efficiency; this leads to an accumulation of dust on the filter bags and a continuous rise in differential pressure.

Remedy: Check if the pulse valves are operating correctly (perform a manual trigger test), verify that the air supply pressure is within the rated range (typically 0.3–0.6 MPa), and ensure the pulse controller is functioning properly.

Cause 2: Sudden increase in inlet dust concentration. If production conditions change (e.g., new equipment is added or output increases significantly) and the inlet dust concentration exceeds design specifications, the rate of dust accumulation on the filter bags accelerates. If the cleaning frequency cannot keep pace, the differential pressure rises rapidly.

Remedy: Check for any new dust-generating sources that have not been connected to the dust removal system, and determine whether cleaning parameters (such as the cleaning interval) need adjustment—specifically, by shortening the cleaning interval as appropriate.

Cause 3: Condensation on or blinding of the filter bags. If the exhaust gas temperature falls below the dew point, water vapor condenses on the filter bags and mixes with dust to form a hardened, caked layer. Pulse cleaning cannot effectively remove this layer, causing the differential pressure to rise continuously; even increasing the cleaning intensity yields no significant improvement.

Remedy: Check whether the exhaust gas temperature at the dust collector inlet is above the dew point (typically, it should be 10–20°C higher). If condensation occurs, inspect the thermal insulation, raise the exhaust gas temperature, or implement a preheating phase during startup.

Cause 4: Excessive service life of filter bags, resulting in incomplete dust removal. Fine dust permanently clogs the interstitial spaces of the aged filter bag fibers, rendering cleaning ineffective and causing the differential pressure to remain consistently high.

Remedy: If the equipment has been in operation for more than three years and the differential pressure remains high despite a properly functioning cleaning system, consider replacing the filter bags.

Situations Involving Lower-Than-Normal Differential Pressure

Low differential pressure alarms also require attention. Abnormally low differential pressure may indicate:

Filter bag damage—Gas passes directly through the damaged area, reducing resistance and lowering the differential pressure; however, the outlet dust concentration rises significantly. This is the most critical scenario, requiring immediate system shutdown to inspect and replace the filter bags.

Fan failure or severe duct leakage—The actual system airflow drops sharply, causing the differential pressure to decrease, while dust removal performance becomes severely inadequate.

Establishing a Differential Pressure Monitoring Log

It is recommended to record differential pressure readings daily and plot the pressure trends over time. These curves allow for the early detection of abnormal trends and the anticipation of issues, enabling proactive handling rather than waiting for an alarm to trigger a response. Long-term data also helps assess the condition of the filter bags and the efficiency of the cleaning system, providing a basis for equipment maintenance.