Pre filters act as a shield, keeping larger particles from prematurely clogging the HEPA filter, ultimately prolonging the life of the HEPA filter. When airflow is severely restricted by excessively blocked filters, it causes the blower to work a lot harder. This reduces airflow to the micro environment, causing the motors to overheat.
Don’t put yourself, your staff, or your research at risk by neglecting regular maintenance to the blowers. HEPA filters, micro/macro environments, and airflow at the cage level can be severely impaired.