{"id":5334,"date":"2026-04-24T09:05:16","date_gmt":"2026-04-24T01:05:16","guid":{"rendered":"https:\/\/www.bacintl.com\/?p=5334"},"modified":"2026-04-27T08:39:41","modified_gmt":"2026-04-27T00:39:41","slug":"the-working-principle-and-maintenance-of-the-negative-pressure-weighing-chamber","status":"publish","type":"post","link":"https:\/\/www.bacintl.com\/fr\/the-working-principle-and-maintenance-of-the-negative-pressure-weighing-chamber\/","title":{"rendered":"The working principle and maintenance of the negative pressure weighing chamber"},"content":{"rendered":"

I. Working Principle
\nThe negative pressure weighing chamber is a type of local purification and negative pressure isolation equipment. The core lies in the use of vertical unidirectional flow and stable negative pressure to prevent dust from spilling out and protect personnel and the environment, meeting the protection requirements of GMP for the weighing of highly active\/toxic materials.<\/p>\n

\"\"
\n1. Airflow organization (vertical unidirectional flow)
\nThree-stage filtration: Return air first passes through the primary filter (for large particles) \u2192 the intermediate filter (pre-filter, protecting HEPA) \u2192 the high-efficiency HEPA (with a 0.3\u03bcm retention rate \u2265 99.99%). Air flow distribution: The fan sends the clean air into the static pressure box, 90% of which is vertically downward (forming a class 100 \/ ISO5 clean area), 10% of which is a small amount of exhaust air, maintaining a relative negative pressure of -5 to -15 Pa in the operation area.
\nNegative pressure isolation: Air only enters and does not exit. Dust is filtered by the airflow and does not escape, avoiding cross-contamination and occupational exposure.
\n2. Core structure
\nBox: 304 stainless steel, seamless welding, corrosion-resistant, easy to clean.
\nFilter system: Primary G4, intermediate F8, high-efficiency H14\/ULPA.
\nFan + static pressure box: Provide stable pressure and uniform air distribution.
\nControl system: Differential pressure \/ wind speed sensors, PLC, alarm function.
\nII. Maintenance and servicing (GMP compliance)
\n1. Daily maintenance (daily \/ weekly)
\nDaily:
\nCleaning: Wipe the countertop, inner wall, and uniform flow membrane with a dust-free cloth and 75% ethanol to remove residual materials.
\nInspection: Start the machine for 3\u20135 minutes to confirm stable negative pressure (-5 to -15 Pa), wind speed 0.45 \u00b1 0.1 m\/s, no abnormal noise from the fan, and no leakage from the seal.
\nWeekly:
\nCalibrate wind speed \/ negative pressure, record differential pressure (primary \/ intermediate \/ high efficiency).
\nCheck sealing strips, exhaust vents, lighting \/ ultraviolet lamps (if any).
\nClean the return air filter and the surface of the primary filter.
\n2. Regular maintenance (monthly \/ quarterly \/ annually)
\nMonthly:
\nPrimary filter: Clean or replace (3\u20136 month cycle, replace when the differential pressure exceeds the initial value by 2 times).
\nIntermediate filter: Check the differential pressure, replace every 6\u201312 months.
\nBox \/ pipeline: Conduct smoke testing for leaks to ensure no dust escapes.
\nQuarterly:
\nCalibrate wind speed sensor (error \u2264 \u00b10.05 m\/s), differential pressure gauge.
\nCheck fan bearings, motor insulation, and tighten electrical connections.
\nAnnually:
\nHEPA integrity: Leak detection with PAO\/DOP, replacement if the leakage rate is > 0.1%.
\nHigh-efficiency filter: Replace every 1\u20132 years, or replace when the differential pressure exceeds the initial value by 50%.
\nUltraviolet lamp: Replace (lifespan approximately 9000 hours, intensity \u2265 70\u03bcW\/cm\u00b2).
\nComprehensive verification: Cleanliness, negative pressure, air flow direction, noise (\u2264 65 dB).
\n3. Key compliance points for filter replacement
\nBefore replacement: Shut down, disconnect power for 10 minutes to release static electricity; clean the interior of the box.
\nHigh-efficiency replacement:
\nRemove the uniform flow membrane, loosen the pressure frame, remove the old HEPA (remove the sealing rubber strip together).
\nInstall the new HEPA according to the airflow arrow direction, press the four sides evenly, and ensure there is no gap in the seal.
\nLeak detection: Scan the frame and filter material with PAO, and it is qualified if there is no leakage.
\nAfter replacement: Record the model, differential pressure, and replacement date, and file for future reference.
\n4. Common faults and handling
\nInsufficient negative pressure: Check for door \/ sealing strip leakage, blockage of primary \/ intermediate filters, insufficient fan speed \u2192 Clean \/ replace filters, tighten the seal, and inspect the fan.
\nUneven wind speed: Blocked uniform flow membrane, local leakage of HEPA \u2192 Clean the uniform flow membrane, detect and replace the HEPA.
\nAbnormal differential pressure: Overdue filter, leakage of seal \u2192 Replace the filter, redo the seal.
\nIII. Maintenance cycle table (quick reference)<\/p>\n\n\n\n\n\n\n\n\n\n\n
Project<\/td>\nCycle<\/td>\nStandard \/ Action<\/td>\n<\/tr>\n
Filtre primaire<\/td>\nMonthly cleaning, with replacement every 3 to 6 months<\/td>\nPressure difference \u2264 2 times the initial value<\/td>\n<\/tr>\n
Filtre \u00e0 moyenne efficacit\u00e9<\/td>\nReplace every 6 to 12 months<\/td>\nPressure difference \u2264 2 times the initial value<\/td>\n<\/tr>\n
High-efficiency HEPA<\/td>\n1 to 2 years, or a pressure difference exceeding 50%<\/td>\nPAO leak test passed<\/td>\n<\/tr>\n
Wind speed \/ Negative pressure calibration<\/td>\nEach season<\/td>\nWind speed: 0.45 \u00b1 0.1 m\/s, negative pressure: -5 to -15 Pa<\/td>\n<\/tr>\n
Box cleaning<\/td>\nDaily<\/td>\nDust-free cloth + 75% ethanol<\/td>\n<\/tr>\n
Smoke leak detection<\/td>\nMonthly<\/td>\nNo dust leakage<\/td>\n<\/tr>\n
Ultraviolet lamp replacement<\/td>\nEvery 3 years<\/td>\nIntensity \u2265 70 \u03bcW\/cm\u00b2<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

IV. Key Compliance Points
\nContinuous Negative Pressure: During operation, it is strictly prohibited to open the door or break the seal to prevent environmental contamination.
\nTraceable Records: Pressure difference, air velocity, leak detection, and replacement records must be kept for at least 5 years, in accordance with GMP audit requirements.
\nSpecial Tools: Use dust-free tools for cleaning and maintenance to avoid secondary contamination.<\/p>","protected":false},"excerpt":{"rendered":"

I. Working Principle The negative pressure weighing chamber is a type of local purification and negative pressure isolation equipment. The core lies in the use of vertical unidirectional flow and stable negative pressure to prevent dust from spilling out and protect personnel and the environment, meeting the protection requirements of GMP for the weighing of […]<\/p>","protected":false},"author":3,"featured_media":5335,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[92],"tags":[],"class_list":["post-5334","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry-technology"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.bacintl.com\/fr\/wp-json\/wp\/v2\/posts\/5334","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.bacintl.com\/fr\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.bacintl.com\/fr\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.bacintl.com\/fr\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/www.bacintl.com\/fr\/wp-json\/wp\/v2\/comments?post=5334"}],"version-history":[{"count":2,"href":"https:\/\/www.bacintl.com\/fr\/wp-json\/wp\/v2\/posts\/5334\/revisions"}],"predecessor-version":[{"id":5337,"href":"https:\/\/www.bacintl.com\/fr\/wp-json\/wp\/v2\/posts\/5334\/revisions\/5337"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.bacintl.com\/fr\/wp-json\/wp\/v2\/media\/5335"}],"wp:attachment":[{"href":"https:\/\/www.bacintl.com\/fr\/wp-json\/wp\/v2\/media?parent=5334"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bacintl.com\/fr\/wp-json\/wp\/v2\/categories?post=5334"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bacintl.com\/fr\/wp-json\/wp\/v2\/tags?post=5334"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}