ValuPrep syringe filters are reliable, highquality syringe filters for HPLC and UHPLC sample processing and clarification. Syringe Filters. Apply gentle pressure to begin filtration. (A gentle pressure helps assure maximum throughput.) CAUTION: As the filter removes particulate, filtration will become more difficult (the syringe plunger will be harder to use) and pressure will rapidly increase on the filter. Change filters when resistance becomes excessive. Failure to change filter may result in membrane rupture, which results in particulate contaminating the filtrate. These filters are for single use only.