Factory Report Passed but On-Site Leak Test Failed: Common Causes

For cleanroom project teams, this is one of the most frustrating situations.

Every high-efficiency filter arrives with a complete factory test report. Efficiency, resistance, and leak-test data all meet the requirements. The packing list is signed, the filters are stored, and installation proceeds according to plan. Yet when the on-site aerosol leak test begins, the photometer immediately alarms.

Is the factory report falsified? In the vast majority of cases, no.

The problem usually lies in the journey between "factory-qualified" and "on-site qualified," a stage that is rarely monitored end to end.

Factory Qualified Does Not Mean Intact on Arrival

A HEPA or ULPA filter can leave the factory in perfect condition, but it is not an indestructible steel box. The media is ultrafine glass fiber, often only a fraction of a millimeter thick. The media pack is bonded to the frame with potting compound. This structure performs well under design airflow conditions, yet it can be affected by non-design conditions such as impact during handling, vibration during transport, or temperature and humidity fluctuations in storage.

We have observed several typical forms of transit or storage damage:

Micro-cracks in the potting compound.

The seal between the media pack and the frame is intact at the factory. Continuous vibration during transport, however, can create fine cracks at the interface between the compound and the metal frame. These cracks are invisible to the naked eye and do not appear during the factory scan. On site they become leak paths, and the photometer detects abnormal signals around the frame.

Localized media damage.

This is the most direct and common issue. Impacts during handling, supporting the filter by the media instead of the frame during installation, or accidental contact with tools can tear or puncture the media. Even a few millimeters of damage is enough for aerosol particles to pass through in large numbers.

Moisture absorption during storage.

If high-efficiency filters are stored for extended periods in uncontrolled environments before installation, the media can absorb moisture from the air. Damp media loses strength and becomes more vulnerable to damage during later handling. Fiber structure may also undergo irreversible expansion and deformation, affecting both resistance and efficiency. If any residual dust is present on the surface, moisture can cause caking and result in abnormally high initial resistance after installation.

A Practical Approach When On-Site Leak Testing Fails

When an on-site leak test triggers an alarm, we recommend that project teams pause before requesting a return and follow a quick diagnostic sequence:

• Check the frame seal first. In many cases the leak source is not the media but the installation sealing surface. Confirm that the gel is fully filled and the knife edge is correctly seated, or that mechanical compression bolts are tightened evenly. Only after the frame seal is verified should the filter itself be removed for inspection.
• Visually inspect the media surface under good lighting. Look for creases, punctures, or signs of edge delamination.
• Review transport and storage records. Was the filter subjected to heavy loads after arrival? Were rain and moisture protection measures in place on site? How long and under what conditions was the filter stored before installation?

These steps help distinguish whether the issue originates from filter quality or from intermediate stages such as transport, storage, and installation. In many cases the latter is the real cause.

What We Do as a Supplier

For a filter supplier, shipping a qualified product from the factory is only the first step. Ensuring that the filter arrives intact and performs correctly in the cleanroom is the complete delivery that customers actually need.

This is why we focus on several key areas:

Packaging design.

Each high-efficiency filter is packed in an individual rigid carton with full-face cushioning that protects the media. The carton is clearly marked with moisture protection, crush resistance, and "this side up" instructions. For large shipments we add vibration-damping layers on the pallet to reduce the effect of low-frequency transport vibration on the potting compound.

Potting process.

We use two-component polyurethane potting compound. After curing, its toughness and adhesion are verified through transport vibration simulation tests to ensure that micro-cracks do not form under normal shipping conditions. Every filter undergoes a full aerosol scan of the potting groove before leaving the factory. This is a non-negotiable quality step.

On-site support.

We provide unpacking and inspection guidelines for project teams. When needed, we can arrange technical personnel to supervise installation and assist with leak testing. If an on-site leak test fails, we respond quickly to help diagnose the cause. If the issue is related to sealing or installation, we assist with adjustment. If the filter has been damaged in transit, we initiate replacement. The goal is to keep the project moving without spending unnecessary time on responsibility debates.

A filter that leaves the factory with a clean report still needs careful handling through transport, storage, and installation. Paying attention to these intermediate steps is often the difference between a smooth commissioning and repeated leak-test failures.