The cleaning frequency of high-efficiency filters (HEPA/ULPA) should be comprehensively determined based on their type, usage environment, and the accompanying pre-filtration system. However, it should be clear that the vast majority of high-efficiency filters are made of disposable filter materials (such as glass fiber, PTFE membrane, etc.), and it is strictly prohibited to reuse them after cleaning. The following is the specific explanation：

I. Why can’t high-efficiency filters usually be cleaned?
The filter material of high-efficiency filters is ultrafine fibers (with diameters ranging from 0.5 to 2μm), which form dense pores (below 0.3μm) through a complex three-dimensional structure. Particles are captured by principles such as interception, diffusion, and inertia.
During cleaning (such as with water, cleaning agents, or compressed air), the structure of the filter material can be damaged, causing fiber breakage, enlarged pore size, and a significant drop in filtration efficiency (possibly from 99.97% to below 90%).
The pollutants adsorbed by the filter material (such as bacteria and chemical particles) cannot be thoroughly removed, and after cleaning, they may become secondary pollution sources.
The sealing rubber strips and frames of some filters may age due to contact with liquids or cleaning agents, resulting in air leakage.
Ii. Special Circumstances That Can be “cleaned” (Limited to a few types only)
A few specially designed high-efficiency filters (such as those made of metal mesh and used in low-pollution environments) may allow for limited cleaning, but must meet the following requirements:
Marked as “washable”: The manufacturer shall specify the cleaning method (such as blowing with compressed air or soaking in neutral detergent).
The cleaning frequency is strictly limited.
Low-pollution environments (such as ordinary laboratories): Clean once every 3 to 6 months, and the cleaning frequency should not exceed three times (replacement is necessary if it exceeds this limit).
Moderately polluted environments (such as food workshops): Cleaning is not recommended. Direct replacement is more reliable.
After cleaning, a leak test must be conducted. A DOP/PAO leak test should be carried out after each cleaning to ensure that filtration efficiency and sealing performance are not compromised.
Iii. Core maintenance Method to replace “cleaning”: Extend lifespan through pre-filtering
The lifespan of high-efficiency filters mainly depends on the concentration of pollutants upstream rather than “cleaning”. The correct approach is:
Strengthen the maintenance of the pre-filter
Primary filter (intercepting particles ≥5μm): Clean (washable) or replace every 1-2 weeks.
Medium-efficiency filters (intercepting particles ≥1μm): Replace every 1-3 months (non-washable type).
The pre-filter can block over 80% of large particle pollutants, reduce the load on the high-efficiency filter, and extend its replacement cycle (from 6 to 12 months to 1 to 3 years).
Determine the replacement timing by pressure difference:
When the resistance of the high-efficiency filter reaches twice the initial resistance (or the upper limit specified by the manufacturer, such as 300Pa), it must be replaced. Do not force its use just because the “time is not up”.
Summary
Conventional high-efficiency filters: Cleaning is prohibited. The replacement time should be determined by maintaining the pre-filter and monitoring the pressure difference (generally 1-3 years, depending on the environment).
Special washable type: It is necessary to strictly follow the manufacturer’s instructions, limit the number of cleaning times (≤3 times), and leak detection must be carried out after each cleaning.
The core of maintenance is “preventing clogging” rather than “cleaning and repairing”. Blind cleaning may instead damage the filtration performance and increase the risk of pollution in the clean environment.