Clearing the Inlet: Restoring Flow to Online Ammonia Analyzers

Clogging of the sample inlet and sampling lines is one of the most frequent faults in online ammonia nitrogen analyzers. Because these instruments operate continuously in wastewater plants and industrial settings, suspended solids, reagent crystals, and biological slime gradually accumulate inside narrow tubing—often only 0.8 to 2.0 mm in diameter—interrupting sample delivery and causing data loss, alarms, or measurement bias. Restoring normal operation requires a systematic approach: stop and locate, clean by type, verify, and prevent recurrence.

Stop and Locate the Blockage

When the analyzer reports “sampling timeout” or “abnormal flow,” or when the sampling pump sounds strained and no liquid movement is visible, stop the instrument immediately and cut off power and reagent supply to prevent pressure buildup from worsening the blockage or damaging the lines. Disconnect the sampling and reagent lines separately and introduce compressed air at 0.2–0.3 MPa into each. 

If airflow is restricted in the sampling line, the blockage lies in the sampling section—the intake port, pre-filter, or main sampling tube. If the reagent line is restricted, the problem is in the reagent delivery path, such as the reagent bottle outlet, reagent tubing, or injection valve. Common blockage points also include tube elbows, solenoid valve cores, and the measurement cell inlet.

Clean According to the Nature of the Blockage

The type of deposit determines the cleaning method. For suspended particles or algae, use a dedicated tube cleaner for gentle clearing or flush the line with high-pressure clean water in the reverse direction until flow is restored. For reagent crystallization—such as mercury iodide precipitate from Nessler’s reagent—prepare a dissolving solution such as dilute hydrochloric acid, soak the tubing for a period, and then rinse thoroughly, ensuring the solution is compatible with the tubing material to avoid corrosion. 

For biological slime, circulate an enzyme-containing cleaner to break down organic deposits, followed by distilled water to remove all residues before resuming analysis. If the blockage is severe at a bend or fitting and cannot be cleared, replace that section with tubing of the same specifications, such as PTFE, and ensure connections are tight and leak-free. 

When the injection valve itself is clogged, disassemble the valve assembly and wipe the valve core and seat with a lint-free swab dipped in cleaning solution, checking that seals remain intact during reassembly.

Verify and Prevent Recurrence

After cleaning, reconnect the lines in reverse order of disassembly, check seals for aging or damage, and perform a leak test by introducing compressed air at 0.1–0.2 MPa and applying soapy water to each joint. 

Start the instrument and run a blank test with deionized water to confirm stable readings and proper color development. If the blank value is abnormal, recheck whether cleaning was thorough or recalibrate the zero point.