What maintenance work should be carried out regularly for the negative pressure weighing chamber?

Regular maintenance of the negative pressure weighing chamber is the key to ensuring its stable performance, meeting cleanliness standards, and extending the service life of the equipment. The following are the specific maintenance tasks and key points classified by maintenance cycle (daily, weekly, monthly, quarterly, and annual) :
I. Daily Maintenance
1. Cleaning and disinfection
Operation surface/equipment surface: Wipe with 75% ethanol or special disinfectant to remove residual dust and material particles.
Floor: Clean with a vacuum cleaner or a wet mop to prevent water accumulation from causing mold growth.
Waste disposal: Timely clear the waste generated during the weighing process, place it in a dedicated sealed container, and handle it according to regulations.
2. Check the operating status
Negative pressure monitoring: Observe the reading of the differential pressure gauge to ensure that the negative pressure value is within the design range (usually -5Pa to -10Pa). If the pressure difference is constant (such as a decrease in the absolute value), it is necessary to check for filter blockage or sealing issues.
Abnormal noise/odor from the equipment: Check if there is any abnormal noise or overheating during the operation of the fan or motor. If any problem is found, stop the machine immediately and report for repair.
Lighting/Ultraviolet lamp: Confirm that the lamp is working properly. If the ultraviolet lamp irradiation time is insufficient, extend the disinfection time or replace the lamp tube.
Ii. Weekly maintenance
1. Cleaning/replacement of the primary filter
Disassembly and cleaning: Remove the primary filter (mostly made of washable non-woven fabric or metal mesh), rinse it with clean water, and dry it. If it is damaged or severely dirty, replace it directly.
Installation reset: Ensure that the filter is installed tightly to prevent air leakage from affecting the negative pressure effect.
2. Calibration of weighing instruments
Calibrate electronic balances and other weighing tools (using standard weights), record the calibration results, and ensure that the weighing accuracy meets the requirements.
3. Inspection of sealing performance
Check whether the sealing strips of the weighing room door and the transfer window are aged or damaged and whether they are tightly closed. If there are any problems, replace the sealing strips in time.
Iii. Monthly Maintenance
1. Inspection/replacement of medium-efficiency filters
Pressure difference detection: Compare the pressure difference before and after the medium-efficiency filter. If the pressure difference exceeds the initial value by 1.5 to 2 times (for specific details, refer to the equipment manual), the filter needs to be replaced.
Direct replacement: If the usage frequency is high or the amount of material dust is large, even if the pressure difference does not meet the standard, it is recommended to replace the medium-efficiency filter regularly every 3 to 6 months.
2. Maintenance of fans and motors
Operating parameter detection: Use a multimeter to measure whether the motor voltage and current are stable and ensure that the fan speed is normal.
Lubrication and maintenance: Add an appropriate amount of lubricating oil to the fan bearings (by the model and dosage specified in the equipment manual) to reduce wear.
3. Cleanliness test
Use a dust particle counter to detect the number of suspended particles in the weighing chamber to confirm whether the cleanliness grade (such as ISO 8 grade) meets the standards. If it exceeds the standard, filter leakage or abnormal airflow needs to be investigated.
Iv. Quarterly maintenance
Performance evaluation of high-efficiency filters
Wind speed detection: Use an anemometer to measure the wind speed at the outlet surface of the high-efficiency filter. It should conform to the design value (usually 0.3-0.5m/s). If the wind speed drops by 15%-20%, the filter may need to be replaced.
Leakage detection: Scan the frame and filter material of the high-efficiency filter through smoke testing or a particle counter to check for any leakage points. If there is any leakage, it should be repaired or replaced in time.
2. Electrical system inspection
Professional electricians should check whether the circuit connections are firm, without any looseness, aging, or damage, to ensure reliable grounding of the equipment and avoid the risk of electric leakage.
Test whether the emergency stop switch and alarm device function properly to ensure that the machine can be stopped quickly in an emergency.
3. Airflow direction test
Use a smoke generator or silk thread to observe the direction of the airflow. Confirm that the airflow is evenly supplied from the high-efficiency filter at the top, and then discharged from the bottom or side after passing through the weighing platform. There should be no airflow short circuit or vortex phenomenon.
V. Annual Maintenance (or Performance Verification)
Comprehensive performance verification
Third-party testing: Entrust a qualified institution to conduct annual testing, and the items include:
Static pressure difference: Confirm that the negative pressure value meets the design requirements.
Air change rate: Verify the supply and exhaust air efficiency (usually required to be ≥15 times per hour).
The number of suspended particles and the content of microorganisms (such as settling bacteria): Comply with the standards of clean areas (for the pharmaceutical industry, GMP requirements must be met).
Issue a report: Adjust the maintenance plan based on the test results. If the performance of the high-efficiency filter is substandard, it needs to be replaced as a whole.
2. Major equipment overhaul
Comprehensive filter replacement: If the high-efficiency filter has been in use for more than 2-3 years (or the detection shows a decline in efficiency), it needs to be replaced as a whole, and leakage tests and air velocity uniformity adjustments should be carried out.
Seal update: Replace all aged sealing strips and gaskets to ensure the airtightness of the weighing chamber.
Fan performance test: Check whether the air volume and air pressure of the fan meet the standards. Replace the fan or motor if necessary.
3. Archiving of document records
Sort out the annual maintenance records, test reports, filter replacement records, etc., file and preserve them for traceability, and comply with GMP and other compliance requirements.
Vi. Special Maintenance Scenarios
Restart after a long period of downtime.
Thoroughly clean the weighing chamber, replace the primary and medium-efficiency filters, and conduct leakage detection on the high-efficiency filter.
Run the equipment unloaded for more than 2 hours, and only put it into use after testing that the negative pressure, air velocity, and cleanliness meet the standards.
2. After use with high dust or special materials
If high-viscosity, hygroscopic, or toxic and harmful materials are being weighed, the cleaning frequency should be increased. If necessary, the filter should be specially cleaned or replaced in advance.
Maintenance Precautions
Personnel qualifications: Operations such as electrical maintenance and high-efficiency filter replacement must be carried out by professional technicians or the manufacturer's after-sales service to prevent equipment damage due to improper operation.
Record completeness: Each maintenance must be filled out in detail in the "Equipment Maintenance Record", including time, content, model of replaced parts, operator, and other information.
Spare parts management: Stock up on commonly used spare parts in advance (such as primary and medium efficiency filters, and sealing strips) to ensure timely maintenance and reduce downtime.
Through systematic and regular maintenance, the negative pressure control capacity, cleanliness and operational stability of the negative pressure weighing chamber can be effectively guaranteed, the risk of contamination can be reduced, and the production compliance requirements of the pharmaceutical, chemical, and other industries can be met.