The core principle of the negative pressure weighing chamber is: through vertical unidirectional flow + local exhaust to form a stable negative pressure, locking dust / pollutants within the operation area and preventing them from leaking out, while ensuring the cleanliness of the operation area.
I. Core Structure (Key Components of Air Flow Path)
Primary / Intermediate Filter: Pre-filters large particles to protect the fan and the high-efficiency filter.
Centrifugal Fan: Provides power to drive the air circulation and exhaust.
High Efficiency Filter (HEPA): Captures particles of 0.3μm with a retention rate of ≥ 99.99%, ensuring the cleanliness of the supply air.
Equalizing Mesh / Equalizing Membrane: Forms a uniform vertical laminar flow (about 0.45m/s).
Return / Exhaust System: Collects the dust-containing air flow, partially recycles and partially discharges.
Pressure Difference Control System: Maintains a relative negative pressure of the operation area to the external environment (usually -15~-30Pa).
II. Operating Process (Air Flow and Negative Pressure Formation)
Return Air Purification
Dust-containing air in the operation area enters through the bottom return mesh, and passes through the primary / intermediate filters successively to remove large particles.
Supply Air Purification
The purified air is sent by the fan into the high-efficiency filter to achieve ISO 5 cleanliness.
Air Flow Distribution (Key)
Approximately 90% of the clean air: Forms a vertical unidirectional flow through the equalizing mesh, covering the operation area downward, and carrying the dust back to the return area.
Approximately 10% of the clean air: Directly discharged outside the equipment.
Negative Pressure Formation
Because the exhaust volume is greater than the return volume, the air pressure in the operation area is lower than the external environment, forming a stable negative pressure, and the air flow can only flow from outside to inside, completely preventing the dust from leaking out.
Circulation and Monitoring
Dust-containing air flow is continuously filtered, purified, and sent back for circulation, forming a closed loop; pressure difference / wind speed sensors monitor in real time, and issue alarms for abnormalities.
III. Core Function
Prevent Leakage: Negative pressure + vertical flow dual locking of dust, protecting personnel and the environment.
Prevent Cross-Contamination: Mainly self-circulation, without affecting the overall pressure difference of the room.
Clean Operation: Meets the cleanliness and safety requirements of GMP/ISO for the weighing of highly active and highly toxic materials.