Methods and apparatus for increasing the duration of uninterrupted filtering flow by using crossflow filtration and ultrasonic energy in difficult to filter process liquids (e.g. of the kind having (1) a carrier liquid, (2) coalescing solids particles which tend to adhere and bridge filter element gaps sized substantially larger than such particles, and (3) larger impurity elements to be filtered out of such process liquid and sized larger than such filter element gaps).