Why do you need to perform DOP leak test on ultra-clean bench high efficiency filter?

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Why do you need to perform DOP leak test on ultra-clean bench high efficiency filter?

1. Overview

If the high-efficiency filter or its installation has defects such as small holes in the filter itself or cracks formed during installation, the desired purification effect will not be achieved. Therefore, after installing or replacing a high-efficiency filter, it's essential to conduct a leak test on both the filter and the mounting connection to ensure proper performance.

2. Purpose of Leak Detection

The main goal of leak detection is to identify any flaws in the high-efficiency filter or its installation by measuring the amount of leakage. This helps in taking necessary corrective actions to maintain the system’s integrity and effectiveness.

3. Scope of Leak Detection

Leak detection is typically performed in clean areas, laminar flow benches, and on high-efficiency filters installed on equipment. It ensures that all critical components are free from leaks that could compromise air quality.

4. Common Leak Detection Methods

The most commonly used method is the DOP (Di-Octyl Phthalate) leak test, which involves using DOP solvent as a dust source and an aerosol photometer to detect leaks. Another method is the particle counter scanning technique, which uses atmospheric dust as a source. However, since the particle counter provides cumulative readings, it's less efficient for scanning. In contrast, the DOP method allows for faster and more accurate detection, especially when smoke is introduced to enhance visibility. This makes the DOP method widely adopted globally.

5. DOP Method Leak Detection

5.1 Working Principle

The DOP method involves introducing DOP aerosol on the upstream side of the tested high-efficiency filter. The aerosol particles, which are spherical and have a molecular weight of 390.57, are collected on the downstream side using a photometer. The photometer measures the scattered light generated by the dusty air, converting it into an electrical signal and displaying the relative concentration of the aerosol. This test essentially measures the penetration rate of the high-efficiency filter.

5.2 Materials and Instruments

- DOP solvent (dust source)

- DOP generator (produces aerosol under pressure or heat)

- Aerosol photometer (measures and displays aerosol concentration; must be calibrated within its validity period)

- Nitrogen gas

- Epoxy resin silica gel

- Spare high-efficiency filter of the required model

5.3 Leak Test Procedure

5.3.1 Preparation

Prepare the necessary equipment and the layout of the air supply ducts in the area to be tested. Coordinate with the HVAC company to perform tasks like sealing or replacing the high-efficiency filter on the day of testing.

5.3.2 Testing Steps

1. Ensure the DOP solvent level in the generator is above the minimum. If low, refill it.

2. Connect the nitrogen bottle to the generator and turn on the temperature control until the indicator changes from red to green (around 390–420°C).

3. Attach one end of the test hose to the upstream port of the photometer and the other to the inlet side of the high-efficiency filter. For system leak tests, introduce DOP smoke directly into the air conditioner (avoiding absorption by internal filters). If the DOP generator is too small, place it in the static pressure box of the filter or at the fan inlet.

4. Turn on the nitrogen valve, set the pressure between 0.05–0.15 MPa, and slowly open the oil valve of the generator. Adjust the photometer reading to 10–20 and stabilize before recording the upstream concentration.

5. Place the other end of the test hose on the downstream port of the photometer and scan the filter outlet and frame. Keep the sampling head about 3–5 cm away from the filter, moving at a speed below 5 cm/s. Inspect the entire filter material, seal joints, and support frames for leaks or damage.

6. If the photometer shows a penetration rate below the acceptable standard, use epoxy resin silica gel to seal the leak or tighten bolts. If needed, replace the filter and re-scan until the reading is within the acceptable range.

7. Document the findings and mark the sealed areas clearly.

5.3.3 Acceptance Criteria

- For 100,000-class clean zones: Filter efficiency should be >95% (photometer reading <5)

- For 10,000-class clean zones: Filter efficiency should be >99.97% (photometer reading <0.03)

6. Notes

6.1 DOP leak tests must be conducted after installing or replacing a high-efficiency filter. In clean areas above 10,000-class, annual testing is typical, while septic areas may require biannual checks. If there are significant changes in dust levels, wind speed, or bacterial counts, a leak test should also be performed.

6.2 DOP contains a benzene ring and is suspected to be carcinogenic. The U.S. has developed an alternative called Emery 3004, which follows the same principles but uses a different dust source.

This process ensures that only high-efficiency filters that pass strict inspection are used in ultra-clean workbenches, guaranteeing reliable performance during production and testing.