What factors need to be considered for the negative pressure laminar flow weighing chamber

What is the differential pressure standard of the negative pressure weighing hood? What is the pressure difference between the inside and outside of the hood? At present, there is no clear regulation, in the design of the negative pressure weighing hood, the designer according to the exhaust air volume of 10%-15%, and 85%-90% of the return air volume design, can achieve the weighing hood internal micro negative pressure environment, and then with the internal airflow flow test, can meet the production demand of the negative pressure difference standard.

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First, the determination of the area of the operation area The specific area of the operation area needs to 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 way of blanking, etc., and the height of the workshop should also be considered. 2. Temperature and humidity control methods and requirements Temperature and humidity parameters are generally not controlled according to process requirements. If the operating area is 3 m2 and used continuously for more than 3 h, the design should take into account cooling control.

There are usually 2 ways to control cooling: water coil cooling and air cooling. 3. Illuminance and noise requirements When selecting the model, the illumination of the negative pressure protection device is usually not less than 300 lx; The noise is usually no more than 75 dB.

Fourth, cleanliness requirements often some users think that the operation area of the weighing protection device is laminar flow, so the cleanliness should reach Class A. In fact, the regulations specify that the air cleanliness level in the area is the same as that of the background room. 5. Sealing and integrity test of high-efficiency filter Negative pressure protection devices are usually equipped with DOP detection ports, which can be used for filter integrity testing.

6. Laminar flow wind speed and centrifugal fan requirements The wind speed design requirements of the negative pressure protection device are consistent with other A-level laminar flow, that is, M s 20%, which is usually designed to be manually or automatically adjustable according to the actual situation (**Wind speed monitoring). If ** wind speed monitoring is used, it needs to be equipped with a wind speed sensor. The centrifugal fan can control the wind speed, and when the wind speed of the fan does not meet the requirements, it is inductively transmitted to the inverter through the wind speed sensor, and the inverter adjusts the motor frequency.

When there is an abnormality in the fan, it can be displayed through the filter differential pressure gauge and the touch screen. 7. Monitoring and alarm of primary, medium and high efficiency filters and fans When monitoring and recording the use of primary, medium and high efficiency filters and the operation of fans, it can be equipped with 4 differential pressure sensors: control indoor and outdoor negative pressure, intermediate and medium efficiency resistance, air supply efficiency resistance, and exhaust efficiency resistance.

At the same time, its resistance to the flow equalizer membrane and the primary, medium and high efficiency filters should be displayed on the touch screen. The differential pressure sensor adopts PLC controller** to dynamically control the working state of the weighing room, which can be stored, printed and displayed, and can be automatically corrected when it deviates from the set working state, and the correction has a deviation alarm. 8. Other The size limit of the actual plant site should be taken into account when selecting the model, especially the width should usually be added to the size of 650 800 mm (mechanical area).

When designing a new plant, consideration should be given to equipping the plant with a mechanical room to facilitate routine maintenance.