1. Part of users when maintain the fuel filters, they lose the upper and lower sealing ring and oil cover, when let the oil flow without being filtrated by element and flow to the center of the element from the gap between the element and filter cap, which makes the fuel filter lose the filtration function 

2. Part of users bottom up the pallet of fuel filter and spring and even throw it, which makes the in and out oil of the filter lid in open state, then the fuel enters to the fuel injection pump with being filtrated