fine-mesh screen, dirt, sediment, and other foreign matter are  removed and settle to the bottom of the housing. At regular  intervals, the cover is removed, and the screen and housing  cleaned with a solvent. Oil screen filters are used mostly as  suction filters on the inlet of the oil pump. The Cuno oil filter has a cartridge made of disks and  spacers. A cleaner blade fits between each pair of disks. The  cleaner blades are stationary, but the disks rotate when the  shaft is turned. Oil from the pump enters the cartridge well  that surrounds the cartridge and passes through the spaces  between the closely spaced disks of the cartridge, then  through the hollow center, and on to the engine. Any foreign  particles in the oil are deposited on the outer surface of the  cartridge. When the cartridge is rotated, the cleaner blades  comb the foreign matter from the disks. The cartridge of the  manually operated Cuno filter is turned by an external handle.  Automatic Cuno filters have a hydraulic motor built into  the filter head. This motor, operated by engine oil pressure,  rotates the cartridge whenever the engine is running. There is  a manual turning nut on the automatic Cuno filter for rotating  the cartridge manually during inspections. This filter is not  often used on modern aircraft. An oil pressure regulating valve limits oil pressure to  a predetermined value, depending on the installation.  [Figure 6-6]  This valve is sometimes referred to as a relief  valve, but its real function is to regulate the oil pressure at a  preset pressure level. The oil pressure must be sufficiently  high to ensure adequate lubrication of the engine and its  accessories at high speeds and powers. This pressure helps  ensure that the oil film between the crankshaft journal and  bearing is maintained. However, the pressure must not be too  high, as leakage and damage to the oil system may result. The  oil pressure is generally adjusted by loosening the locknut  and turning the adjusting screw.  [Figure 6-10]  On most  aircraft engines, turning the screw clockwise increases the  tension of the spring that holds the relief valve on its seat  and increases the oil pressure; turning the adjusting screw  Full flow spin-on filters are the most widely used oil filters  for reciprocating engines.  [Figure 6-8]  Full flow means that  all the oil is normally passed through the filter. In a full flow  system, the filter is positioned between the oil pump and the  engine bearings, which filters the oil of any contaminants  before they pass through the engine bearing surfaces. The  filter also contains an antidrain back valve and a pressure  relief valve, all sealed in a disposable housing. The relief  valve is used in case the filter becomes clogged. It would open  to allow the oil to bypass, preventing the engine components  from oil starvation. A cutaway of the micronic filter element  shows the resin-impregnated cellulosic full-pleat media that  is used to trap harmful particles, keeping them from entering  the engine.  [Figure 6-9] element is designed with a corrugated, strong steel center  tube supporting each convoluted pleat of the filter media,  resulting in a higher collapse pressure rating. The filter  provides excellent filtration, because the oil flows through  many layers of locked-in-fibers. Hex head screw Copper gasket Filter element Rubber gasket Cover plate Rubber gasket Nylon nut Case housing or canister Figure 6-7.  Housing filter element type oil filter.  Figure 6-8.  Full flow spin-on filter.  Oil Pressure Regulating Valve A canister housing filter has a replaceable filter element  that is replaced with rest of the components other than  seals and gaskets being reused.  [Figure 6-7]  The filter  6-8