The atmospheric pre concentrator is a core equipment used in environmental monitoring for the analysis of volatile organic compounds (VOCs), semi volatile organic compounds (SVOCs), and odorous substances. Its function is to achieve sample concentration and enrichment through low-temperature adsorption, heating desorption, and other technologies. To ensure stable instrument performance, accurate data, and extended service life, comprehensive maintenance is required from daily maintenance, regular upkeep, key component management, and operating standards. The following are detailed maintenance details:
1、 Daily maintenance details
1. Cleaning and dust prevention
-External cleaning: Wipe the instrument casing with a dust-free cloth daily to avoid dust accumulation affecting heat dissipation or blocking the air vents.
-Air inlet protection: The instrument air inlet needs to be equipped with an air filter membrane (such as PTFE material), which should be checked and replaced weekly to prevent particulate matter from entering the internal pipeline.
-Pipeline cleaning: After each sampling, blow the pipeline with high-purity nitrogen for at least 30 minutes to remove residual volatile substances and avoid cross contamination.
2. Flow and pressure monitoring
-Carrier gas stability: Check the pressure of the carrier gas (such as high-purity nitrogen or helium) daily to ensure that the pressure fluctuation range is within ± 5% of the instrument's nominal value.
-Flow calibration: Use soap film flowmeter or electronic flowmeter to calibrate the carrier gas flow rate every month, with an error controlled within ± 2%. Otherwise, adjust the valve or replace the flow controller.
3. Cold trap status check
-Temperature verification: Confirm daily that the actual temperature of the first stage cold trap (-30 ℃~-15 ℃) and the second stage cold trap (-150 ℃~-180 ℃) does not deviate from the set value by more than ± 2 ℃, in order to avoid temperature runaway and a decrease in adsorption efficiency.
-Frost treatment: If frost accumulates on the surface of the cold trap, pause the instrument and wait for the temperature to rise before blowing and melting with dry nitrogen gas. It is strictly forbidden to directly scrape off to avoid damaging the refrigeration module.
4. Filter membrane and adsorbent replacement
-Particulate filter membrane: The primary filter membrane at the inlet should be replaced every two weeks. If there is a lot of dust in the sampling environment, the cycle should be shortened.
-Adsorbent maintenance: Adsorbents such as Tenax, activated carbon, or silica gel need to be replaced regularly according to their usage frequency (usually every 3-6 months). Before replacement, high-temperature activation or nitrogen purging regeneration is required.
2、 Regular in-depth maintenance
1. Maintenance of pipeline system
-Airtightness testing: Conduct a full pipeline pressure test every month, close all outlets and pressurize to 10 kPa. If the pressure drop does not exceed 5% within 10 minutes, it is considered qualified.
-Valve lubrication: Inject a small amount of inert silicone oil (such as DC 200) into the pneumatic valve every quarter to avoid sealing ring wear and gas leakage.
2. Cold trap defrosting and cleaning
-Deep defrosting: Perform a cold trap defrosting once a quarter, start the heating program to room temperature, and rinse the inner wall of the cold trap with anhydrous ethanol to remove volatile residues.
-Sealing inspection: The O-ring at the connection of the cold trap needs to be replaced annually to ensure vacuum sealing.
3. Detector calibration
-FID (Hydrogen Flame Ionization Detector): Check the flow rates of hydrogen, air, and exhaust gas weekly, calibrate the response values with standard methane gas monthly, and ensure a linear error of less than 5%.
-MS (Mass Spectrometry Detector): Perform mass axis calibration every six months and clean the ion source to avoid interference from pollutants in the spectrum.
4. Electrical and control system inspection
-Aging detection of circuits: Check the power lines, signal lines, and connectors for oxidation or damage every year, with a focus on inspecting the cold trap temperature control sensor and solenoid valve circuits.
-Software update: Upgrade instrument control software in a timely manner, fix known vulnerabilities, and optimize collection parameters.
3、 Special maintenance of key components
1. Maintenance of refrigeration system
-Compressor maintenance: Clean the condenser fins annually, check the refrigerant pressure (such as R404A refrigerant), and supplement or replace as necessary.
-Temperature difference control: During the cooling process of the cold trap, a gradient cooling program (such as -1 ℃/min) should be set up to avoid sudden temperature changes that may cause the adsorbent to rupture.
2. Heating desorption module
-Temperature uniformity test: Use thermocouples to detect the temperature distribution of the desorption tube at multiple points every six months, with a deviation of<± 5 ℃.
-Heating wire inspection: Regularly clean the carbonized residue inside the detachment tube to avoid local overheating that may cause the heating wire to melt.
3. Sampling pump and flow sensor
-Pump body lubrication: Special silicone oil is added monthly to the diaphragm pump, and the oil level of the vacuum pump needs to be checked and the pump oil needs to be replaced (once a year).
-Sensor cleaning: Gently wipe the mass flow sensor with an alcohol swab to avoid zero drift caused by dust blockage.
4、 Storage and transportation precautions
1. Long term shutdown protection
-When the instrument is shut down for more than one week, high-purity nitrogen should be used to blow the pipeline and seal the inlet. The cold trap should be kept at a low temperature (below -15 ℃) to prevent deliquescence.
-Run once a month with power on, execute the no-load cycle program, and maintain lubrication of mechanical components.
2. Anti seismic transportation
-During transportation, it is necessary to remove the cold trap and fragile components, use original shock-absorbing packaging, and keep them vertically placed to avoid tilting more than 30 degrees.
5、 Maintain records and safety regulations
1. Log management
-Establish maintenance files to record the maintenance content, replacement part batches, and calibration data for each maintenance, in order to trace the cause of faults.
-Abnormal events (such as sudden pressure changes and signal noise) should be noted in detail and image data should be retained.
2. Safe operation
-When handling high concentration VOCs samples, operate the entire process in a fume hood, wear a gas mask and anti-static gloves.
-It is prohibited to plug and unplug pipelines or replace components with electricity. Before maintenance, the power supply must be cut off and the system pressure must be released.