The working process of the negative pressure weighing chamber

The working process of the negative pressure weighing chamber is designed around "directional air flow control + negative pressure isolation". The core objective is to confine dust, volatile substances and other pollutants within the chamber through strict air flow organization and pressure control during weighing operations, preventing their spread to the external clean area, while ensuring the safety of the operators. The following is the detailed workflow, divided by operation stages:
I. Preparation stage before startup
Environmental and parameter confirmation
Check the surrounding environment of the weighing room: Ensure that the external area (such as the clean corridor) is clean and free of obvious pollution sources to prevent external contaminants from affecting the interior through gaps.
Confirm the equipment status: Check the negative pressure value displayed on the control panel (usually preset -5Pa to -15Pa), the fan operation mode (such as "weighing mode", "standby mode"), and the filter pressure difference (whether the resistance of the primary/high-efficiency filter is within the normal range). If the parameters are abnormal, they need to be investigated first (such as filter blockage, air valve failure).
Preparation of materials and tools
Send the materials to be weighed, clean containers, and weighing tools (such as balances and spatles) into the room through the transfer window or operation port (avoid opening the door directly to bring in external air).
Operators should wear protective equipment that meets the cleanliness level (such as clean suits, gloves, masks, and goggles or respirators should be added when handling toxic materials).
Ii. Startup and Pre-operation Stage
Start the equipment
Press the "Start" button, and the equipment enters the pre-operation state: the fan starts, beginning to supply and exhaust air. Clean air is delivered into the room through the intake system (primary filter → fan → high-efficiency filter), while the exhaust system filters the indoor air (containing pollutants) through the high-efficiency filter and then displaces it outdoors or returns it to the air conditioning system.
At this point, indoor air is "drawn in" through gaps such as operation ports and door seams (due to negative pressure), forming an isolation barrier.
Self-cleaning and parameter stability
Pre-running time: According to the cleanliness requirements (usually Class 5, that is, ISO 8), it needs to run for 15 to 30 minutes to ensure that the indoor dust particle count, settled bacteria, and other indicators meet the standards (some equipment is equipped with a self-cleaning countdown function).
Reconfirm the negative pressure: After the self-purification is completed, confirm that the negative pressure value is stable within the set range through the differential pressure gauge. If the fluctuation exceeds ±2Pa, the air valve (intake/exhaust ratio) needs to be readjusted to balance.
Iii. Weighing Operation Stage (Core Process)
Air flow organization and pollutant control
The operator extends their arm through the operation port into the room and performs operations (such as weighing, portioning, and mixing) on the weighing table. At this moment
The vertical unidirectional airflow (wind speed 0.45-0.55m/s) sent out by the top high-efficiency filter covers the entire operation area, "pressing down" the dust generated by the materials onto the countertop.
The return air outlets under or around the countertop draw in the dusty air, which is then filtered by the high-efficiency filters of the exhaust system before being discharged, preventing the dust from spreading in the room.
The key function of negative pressure: Even if a small amount of dust overflows during operation, as the indoor pressure is lower than the external pressure, the dust will be "sucked back" into the room instead of spreading to the external clean area.
Implementation of operational norms
Avoid quick movements: Reduce the frequent entry and exit of the arm in and out of the operation port to prevent airflow disorder (which may damage the negative pressure barrier).
Material handling: Handle with care when weighing to avoid violent dumping that may cause dust to fly. Spilled materials should be immediately cleaned up with a clean cloth dipped in disinfectant to prevent residual contamination.
Iv. Post-operation cleaning and shutdown stage
Indoor cleaning
After the operation is completed, keep the equipment running (the fan does not stop), and wipe the countertop, side walls, and observation window with 75% alcohol or a special disinfectant to remove residual materials and dust. Detachable parts (such as the weighing platform guardrail) need to be removed for cleaning before being reinstalled.
Cleaning tools (such as clean cloths) should be disposed of as medical waste after use (especially when handling toxic materials) to prevent the removal of contaminants.
Shutdown and parameter recording
After cleaning is completed, press the "Stop" button. The equipment will enter a delayed shutdown state (usually for 3 to 5 minutes) to ensure that all residual contaminants are completely discharged.
Record operation data: Record the operation time, negative pressure value, filter pressure difference, and abnormal conditions (such as parameter fluctuations) in the equipment log or system to facilitate traceability and subsequent maintenance.
V. Special Case Handling (Such as Abnormal Parameters)
If the negative pressure suddenly disappears or turns positive during operation: immediately stop the operation, shut down the equipment, check whether the high-efficiency filter is clogged (excessive pressure difference), whether the exhaust fan has stopped rotating, and whether the sealing at the operation port has failed (such as aging of the sealing strip). After eliminating the faults, restart.
If dust leaks to the outside (such as obvious dust overflow from the operation port): Immediately evacuate the surrounding personnel, turn on the surrounding exhaust system (such as the clean room air conditioning), disinfect the external area after the dust settles, and then inspect the negative pressure and air flow balance of the weighing room.
Summary of core logic
The essence of the working process in a negative pressure weighing chamber is to achieve the dual goals of "no diffusion of pollutants within the operation area and no intrusion of external pollutants" through a closed-loop control of "clean air flow coverage + negative pressure isolation + filtration purification". Each stage must focus on the two core aspects of "stable negative pressure" and "effective filtration" to ensure compliance with the cleanliness and safety requirements for material weighing in industries such as GMP and FDA.