HEPA filter is very delicate and require special care while handling and the installation.
To provide good seal the HEPA is attached to the filter retainer and the clamp mechanism. Sometimes this clamp is spring loaded. It’s crucial that new HEPA is secured in a place ensuring good seal.
After replacement, flow has to adjusted and pressure differential across filter to be checked. It’s necessary to validate the HEPA and its installation, through the integrity test.