The maximum operating pressure indicated refers to the sealing of the system. If the difference of pressure between inlet and outlet port is greater than 20 bar (290 psi) the filter breaks, for this reason it is advisable to check periodically the filter to avoid clogging.
During the installation of the lubrication system, it is possible than foreign materials remain into the tube. The use of the filter is recommended to avoid this contamination to enter the lubrication system damaging the machine and the lubrication plant.