THIS IS A MULTI PURPOSE DESIGN. 1. Additional Filtration 2. Accessory Hardware Adaption In addition to the filtration benefits the HPRA can be used during the installation of a dual pump setup or supply and return oil for twin turbos to eliminate drilling holes in your factory reservoir. The hole marked "pressure relief return" in the picture below, dumps oil back to the oil pan down the front cover. This is a perfect place to return oil from a twin turbo configuration. The Powerstroke uses high pressure oil to activate the injectors. At start-up, the high pressure pump (HPOP) draws oil from the reservoir to start the engine, and the low pressure pump is refilling the reservoir with unfiltered oil until there is engine oil lube pressure. This allows a small amount of dirty oil from the oil pan to reach the HPOP and the injectors every time the truck is started. Small fine debris will pass fairly easily, but larger debris can cause pump or injector damage. In mid year 1999 (Engine Serial Number 1039779), Ford integrated a filter screen into the front cover gasket to catch any large debris before entering the HPOP. This new "gasket" with integrated filter CANNOT be retrofitted into an older engine as the front engine cover was machined differently to accommodate it. If you do use this gasket accidentally, you will crack the front cover causing a very expensive repair bill.