Characteristics and selection factors of negative pressure weighing chamber

A negative pressure weighing room is a kind of local purification equipment specially used for pharmaceutical, microbiological research, and scientific experiments. Negative pressure is generated in the working area to prevent cross-contamination, which is used to ensure a high cleanliness environment in the active area. 

Weighing and packaging dust and reagents in the equipment can control the spillage and rise of dust and reagents, prevent the inhalation hazards of dust and reagents to the human body, and also avoid cross-contamination of dust and reagents, and protect the safety of the external environment and indoor personnel.

1. Structural features

The negative pressure weighing chamber is assembled from the working area, the return air box, the fan box, the air outlet, and the outer box. The control panel is located in the front of the inner working area of the equipment. The control panel adopts a light-touch LED control panel, which can control the start and stop of the fan, adjust the working condition of the fan, and adjust the wind speed required by the working area (when the equipment is installed and used, the working condition needs to be adjusted by special personnel. ). There is a differential pressure gauge next to it, and the resistance of the test filter is also equipped with an exhaust adjustment plate inside the air supply box, which can adjust the exhaust air volume of the equipment within a reasonable range (after the equipment is installed, it is designed by professionals. try, do not adjust it without authorization).

2. Working principle

The negative pressure weighing chamber adopts the form of vertical unidirectional flow, and the return air must be pre-filtered through the primary filter to deal with the large particles of dust particles in the airflow. The pretreated air is then filtered through a medium-efficiency filter to fully protect the high-efficiency filter. Under pressure provided by the centrifugal fan, it passes through the high-efficiency filter to make it meet the requirements of cleanliness. The clean air flow is sent to the air supply box, 90% of which passes through the uniform air supply screen to form a uniform vertical air supply airflow, and 10% passes through the air volume adjustment plate and is discharged from the equipment. All airflows are processed by high-efficiency filters, so there is no residual dust in the air supply and exhaust, which avoids secondary pollution. Due to the formation of a stable one-way flow in the working area, the dust emitted in this area will be captured by the primary and medium-efficiency filters along with the airflow under the influence of the one-way airflow. The equipment has 10% exhaust air, thus forming a negative pressure relative to the external environment, which ensures that the dust in this area will not spread to the outside to a certain extent, and plays a role in protecting the external environment.

3 selection factors

The negative pressure weighing chamber can be selected or customized according to the specific size of the actual use. The following issues should be considered when selecting or customizing:

3.1 Determination of the area of the operation area

The specific operation area should be determined according to the actual situation. For example, there are several operators, how many balances, how many barrels, the size of the barrels, the feeding method, etc. The height of the workshop should also be considered.

3.2 Temperature and humidity control methods and requirements

Temperature and humidity parameters are based on process requirements, and generally do not control if there are no special requirements. If the operating area is more than 3 m2 and it is used continuously for more than 3 hours, cooling control should be considered in the design. There are usually two ways of cooling control: water coil cooling and air cooling.

3.3 Illumination and noise requirements

In the selection, the illumination of the negative pressure protection device is usually not less than 300 Lx; the noise is usually not more than 75 dB.

3.4 Cleanliness requirements

Some users often think that the operating area of the weighing protection device is laminar flow, so the cleanliness must reach Class A. In fact, the regulations clarified that the air cleanliness level in the area should be consistent with the background room.

3.5 Sealing and Integrity Testing of HEPA Filters

The negative pressure protection device is usually equipped with a DOP detection port, which can conduct filter integrity tests.

3.6 Requirements for Laminar Flow Speed and Centrifugal Fan

The wind speed design requirements of the negative pressure protection device are consistent with other A-level laminar flow, that is, 0.45 m/s ± 20%, which is usually designed to be manually or automatically adjustable (online wind speed monitoring) according to the actual situation. A wind speed sensor is required for online wind speed monitoring. The centrifugal fan can control the wind speed. When the wind speed of the fan does not meet the requirements, it is transmitted to the inverter through the wind speed sensor, and the inverter adjusts the motor frequency. When the fan is abnormal, it can be displayed through the filter differential pressure gauge and touch screen.

3.7 Monitoring and alarming the primary, middle, and high-efficiency filters and fans

When monitoring and recording the usage of the primary, middle, and high-efficiency filters and fan operation, it can be equipped with 4 differential pressure sensors: controlling indoor and outdoor negative pressure, primary and secondary efficiency resistance, and high-efficiency air supply resistance, and high-efficiency exhaust resistance. At the same time, its resistance to the equalizing membrane and the primary, middle, and high-efficiency filters should be displayed on the touch screen. The differential pressure sensor adopts the PLC controller to dynamically control the working state of the weighing room online, which can be stored, printed, and displayed. It can be automatically corrected when it deviates from the set working state, and there is a deviation alarm when the calibration is performed.

3.8 Others

The size limitation of the actual workshop site should be considered when selecting the model, especially the width should usually be increased by 650-800 mm (mechanical area). When designing a new plant, consideration should be given to equipping the device with a mechanical room to facilitate routine maintenance.

Wuxi Lenge Purification Equipments Co., Ltd. is a professional purification equipment manufacturer. Suitable for pharmaceuticals, laboratory, food & beverage, electronics, etc. If you are interested in purification equipment, please get in touch with us! You can call 86-510-85189266. Or send an email to export@wxljjh.com.