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Shanghai Hujing Medical Equipment Co., Ltd
Purpose of DOP leak detection for high-efficiency filter of laminar flow ultra clean workbench
Date: 2025-03-13Read: 7
1. Purification effect and installation replacement of laminar flow ultra clean workbench:
If there are defects in the high-efficiency filter and its installation, such as small holes in the filter itself or small cracks formed by loose installation, it will lead to the failure to achieve the predetermined purification effect. Therefore, after the installation or replacement of high-efficiency filters, it is necessary to perform leak detection on the filters and installation connections.
2. Purpose of leak detection
By testing the leakage rate of the high-efficiency filter, defects in the high-efficiency filter and its installation can be identified in order to take remedial measures.
clean bench
3. Leak detection range
Clean areas, laminar flow ultra clean workbenches, and high-efficiency filters on equipment.
4. Leak detection method
The commonly used method for leak detection is the DOP method (which uses DOP solvent as the dust source and cooperates with an aerosol photometer for leak detection), or the dust particle counter scanning method (which uses atmospheric dust as the dust source and cooperates with a particle counter for leak detection). Due to the cumulative reading of the particle counter, it is not conducive to scanning and the inspection speed is slow; In addition, on the upwind side of the tested high-efficiency filter, the atmospheric dust concentration is often low, and it is necessary to supplement smoke to easily detect leaks. The shortcomings of particle counter leak detection can be compensated for by the DOP method, which is widely used for leak detection abroad.
5. DOP method for leak detection
5.1. Working principle
The DOP aerosol is generated on the windward side of the detected HEPA filter as the dust source (DOP is dioctyl phthalate, with molecular weight of 390.57, and the particles are spherical after spray), and the photometer is used for sampling on the downwind side. The collected air sample passes through the diffusion chamber of the photometer, and the scattered light generated by the dust containing gas through the photometer is converted from photoelectric effect and linear amplification to electricity, and quickly displayed by the microammeter, then the relative concentration of the aerosol can be measured. The DOP test actually measures the penetration rate of the high-efficiency filter.
clean bench
5.2. Materials and Instruments
① Dust source (DOP solvent);
② DOP generator is a device that generates smoke. After pouring DOP solvent into the generator container, aerosol smoke is produced under certain pressure or heating conditions and sent to the upwind side of the high-efficiency filter (heating the DOP liquid to form DOP vapor, which condenses into tiny droplets under specific conditions, removing oversized and undersized droplets, leaving only particles of about 0.3 μ m, and the misty DOP enters the air duct);
③ Aerosol photometer (an instrument for measuring and displaying aerosol concentration, which should indicate the validity period of calibration and must be calibrated and within the validity period before use);
④ Nitrogen;
⑤ Epoxy resin silicone;
⑥ Spare high-efficiency filters of the required model
5.3. Leak testing procedure
5.3.1. Leak detection preparation
Prepare the necessary equipment for leak detection and the layout plan of the air supply duct of the purification air conditioning system in the inspection area, and notify the purification air conditioning equipment company to arrive on the day of leak detection for operations such as gluing and replacing high-efficiency filters.
5.3.2. Leak detection operation
① Check if the level of DOP solvent in the aerosol generator is higher than the low level. If it is insufficient, it should be added.
② Connect the nitrogen cylinder to the aerosol generator, turn on the temperature switch of the aerosol generator, and when the red light turns green, it indicates that the temperature has reached (about 390-420 ℃).
③ Place one end of the test hose at the upstream concentration testing port of the aerosol photometer, and the other end at the inlet side (upstream side) of the high-efficiency filter being tested. [System leak detection can directly put DOP smoke into the air conditioner (be careful not to be adsorbed by the filter inside the air conditioner).]; If the DOP generator is too small to reach the specified concentration, it can be placed in the static pressure box of the tested high-efficiency filter, and the laminar flow workbench can be directly placed in the fan suction port. Then, turn on the photometer switch and adjust the test value to "100".
④ Turn on the nitrogen switch, control the pressure at 0.05-0.15Mpa, slowly open the oil valve of the aerosol generator, and control the test value of the photometer to be between 10-20. After the test value stabilizes, input the upstream measured concentration to proceed with subsequent scanning and inspection operations.
⑤ Place one end of the test hose at the downstream concentration testing port of the aerosol photometer, and use the other end, namely the sampling head, to scan the outlet side and bracket of the filter. The sampling head should be about 3-5cm away from the filter, and scan back and forth along the inner frame of the filter. The inspection speed should be below 5cm/s. The testing range includes the filter material of the filter, the connection between the filter material and its frame, the connection between the sealing gasket of the filter frame and the support frame of the filter group, the connection between the support frame and the wall or ceiling, to check for small pinholes and other damages in the filter medium, frame sealing, gasket sealing, and leaks on the filter frame.
Laminar flow ultra clean workbench
⑥ The instrument reading on the photometer is the penetration rate of the high-efficiency filter. When the efficiency of the high-efficiency filter is below the acceptable standard, use epoxy resin silicone to seal the leak or tighten the bolts (if necessary, stop smoking and replace the high-efficiency filter), and then perform scanning inspection until the instrument reading is within the acceptable range.
⑦ Leak detection should be recorded in a timely manner, and a schematic diagram of the application of epoxy resin silicone sealant should be used to mark the leak points.
5.3.3. Acceptable standards
The efficiency of the high-efficiency filter in the 100000 level clean area should be greater than 95% (the indication value of the aerosol photometer instrument should be less than 5);
The efficiency of the high-efficiency filter in the 10000 level clean area should be greater than 99.97% (i.e. the indication value of the aerosol photometer instrument should be less than 0.03).
6. Explanation
6.1. DOP leak detection must be carried out after the installation or replacement of high-efficiency filters; Daily leak detection of high-efficiency filters in clean areas above 10000 levels is generally conducted once a year (sterile areas should be checked every six months); When there are significant abnormalities in dust particle count, settling bacteria, wind speed, etc. during daily monitoring in the clean area, leak detection should also be conducted.
6.2. DOP, as a dust source, contains benzene rings. Although the dust sources are different, the principle and method of leak detection are the same.
