What are the risks of operating ULPA with excessive air volume and surge air volume?

In actual projects, 'over-rating' is more common than imagined.

In order to quickly restore cleanliness during system debugging, the fan is temporarily turned on to the maximum level; or at the moment the valve is switched, the airflow exceeds the design value in a short period of time. These conditions may seem like the air volume is too high, but for products like ULPA, it may not be as simple as a change in resistance.

The core of the problem is not 'whether it can be blown through', but whether the impact of over-rated and impact conditions on the filter material, structure, sealing and efficiency will be exposed after a period of operation.

What happens inside the filter element when it is operating beyond its rated value?

The rated air volume of ULPA usually corresponds to a recommended working range. Beyond this range, several changes occur simultaneously.

By increasing the wind speed. Increased air volume means more airflow per unit area of ​​the filter material. The higher the passing wind speed, the shorter the time the particles stay in the filter material, and the time for interception and diffusion effects is also reduced accordingly. The efficiency data on the inspection report may not directly extend to higher passing wind speed conditions.

Pressure loss increases. This is the easiest change to observe. The resistance increases as the air volume increases, and the pressure loss under over-rated conditions may far exceed the design value. If the fan does not have enough residual pressure, the air volume cannot be increased, but the energy consumption is only pushed up.

The stress on the structure increases. When air flows through the filter media, it exerts forces on the pleats and support structures. Under over-rated conditions, this force is even greater. There may not be any problems in the short term, but in the long run, the risk of pleat deformation and glue seam fatigue will increase.

Vibration and noise changes. After the wind speed increases, the frequency and amplitude of the excitation of the structure by the airflow may change. For device-side applications, this can affect surrounding precision components.

The particularity of impact air volume

Impulse air volume is different from steady-state over-rating. It is a sudden change in pressure or flow in a short period of time.

The source is usually system operations. Rapid opening and closing of valves, starting and stopping of fans, and coordinated switching of multiple devices may cause pressure waves in the pipeline. The peak value of this transient pressure is sometimes much higher than the steady-state resistance.

The way shock damages is cumulative. A single impact may not cause obvious damage, but repeated impacts will subject the structure to alternating loads. The roots of pleats, glue seam interfaces, and outer frame connections are all easily affected parts.

Detection methods have limitations. Factory testing is usually performed under steady-state conditions, and there is no corresponding standard test for performance under impact conditions. This means that whether a product can withstand impact often needs to be evaluated based on actual working conditions, rather than simply comparing a report.

Scenarios that are easily overlooked: Frequent switching of gears during the system debugging phase, frequent automatic valve adjustment movements, and group control start and stop of multiple FFUs. These daily operations may cause repeated impacts.

Which working conditions require special assessment

For the following types of applications, it is recommended to include over-rated and impact conditions in the assessment during the planning stage.

A system with a wide frequency control range. If the fan is to operate within a wide speed range, the air volume corresponding to the highest speed may exceed the filter rating. The duration and frequency of occurrence of this working condition need to be confirmed.

Clean room for quick response to requests. Some processes require rapid changes in the number of air changes, and the system may significantly adjust the air volume in a short period of time.

A system that links multiple devices. The start and stop of a piece of equipment will affect the air volume distribution of the entire pipeline, causing flow fluctuations in the end filter.

Device-side application. The internal space of semiconductor equipment and precision manufacturing equipment is compact, and the EFU fan may be very close to the filter element. The start, stop or speed change of the fan will have a more direct impact on the filter element. In this type of application, the structural strength and support design of the filter element must match the working conditions.

How to judge and deal with

If the project has over-rated or impact conditions, it is recommended to evaluate it in the following way.

Quantify the working conditions first. Clarify what the maximum air volume is, how long it lasts, and how frequently it occurs. Whether it is occasional or continuous, steady state or transient, the processing methods are different.

Provide working condition information to suppliers. Provide the actual operating air volume range, change rate, and start-stop frequency to the supplier so that they can determine whether the product is suitable. This is not a simple question of 'whether the air volume is enough', it requires a combination of structural design and verification data evaluation.

Check structural design. Fold density, support method, colloid type, and frame strength all affect the performance of the product under over-rated conditions. Different products have different design orientations and different applicable working conditions.

Observation means are left during operation. Pressure difference, vibration, and noise can all be used as references for operating status. If abnormal parameters are found under over-rated conditions, it is necessary to evaluate whether to adjust the system or replace the filter element.

Don't compensate long-term by increasing the RPM. If the system needs to continue to exceed rated operation due to high resistance, it means there is a problem with the selection or system configuration itself. The cost of long-term operation beyond operating conditions may be higher than replacing a more suitable filter element.

Project judgment example

In order to meet the rapid recovery requirements, a certain clean room raised the FFU gear from 60% to 100% during debugging. After operation, it was found that the pressure difference reading of the terminal ULPA was on the high side, and some filter elements became pleated and deformed after several months of operation.

The investigation found that the air volume corresponding to the 100% gear exceeded the recommended working range of the filter element. Although there were no obvious problems in a single operation, repeated operation at high speeds, coupled with flow shocks during start and stop, caused the filter element structure to withstand loads beyond the design range.

Treatment direction: Adjust the system operating gear back to a reasonable range, and meet the cleanliness requirements by optimizing the front-stage filtration and airflow organization, rather than increasing the terminal air volume. For deformed filter elements, evaluate the integrity and decide whether to replace them.

The lesson from this case is: the cost of exceeding rated operating conditions is often not present, but after a period of operation. involving When selecting a HEPA/ULPA air filter , checking the operating range and selecting the grade are equally important.

Selection and Acceptance Checklist

About Aili Industrial’s working condition adaptation

The evaluation of over-rated and impact conditions requires looking at product parameters and actual operating conditions together.

Aili Industrial has independent manufacturing capabilities in filters, motors, fans, control systems and sheet metal processing. The product design phase can match the work scope. For projects with special working conditions, the air volume change range, start-stop frequency and structural constraints can be provided together, and whether the working conditions and structural configuration of the filter element are suitable can be evaluated during the planning stage. When the filter is matched with air supply equipment such as FFU and EFU, the air volume range and control strategy can also be confirmed uniformly.

Explaining the actual operating conditions when making an inquiry will help confirm a more matching product configuration. The specific scope of application is subject to product technical information and project confirmation documents.