Safety wire tabs conveniently located  on hex nut for easy access Resin-impregnated,  cellulosic full-pleat media for uniform  flow and collapse  resistance Corrugated center support tube for  maximum resistance to collapse Figure 6-10.  Oil pressure adjustment screw.  Figure 6-9.  Cutaway view of a filter.  counterclockwise decreases the spring tension and lowers  the pressure. Some engines use washers under the spring that  are either removed or added to adjust the regulating valve  and pressure. The oil pressure should be adjusted only after  the engine’s oil is at operating temperature and the correct  viscosity is verified. The exact procedure for adjusting the  oil pressure and the factors that vary an oil pressure setting  are included in applicable manufacturer’s instructions. Usually, the oil pressure gauge indicates the pressure that oil  enters the engine from the pump. This gauge warns of possible  engine failure caused by an exhausted oil supply, failure of  the oil pump, burned-out bearings, ruptured oil lines, or other  causes that may be indicated by a loss of oil pressure. One type of oil pressure gauge uses a Bourdon-tube  mechanism that measures the difference between oil  pressure and cabin, or atmospheric, pressure. This gauge is  constructed similarly to other Bourdon-type gauges, except  that it has a small restriction built into the instrument case,  or into the nipple connection leading to the Bourdon tube.  This restriction prevents the surging action of the oil pump  from damaging the gauge or causing the pointer to oscillate  too violently with each pressure pulsation. The oil pressure  gauge has a scale ranging from 0–200 psi, or from 0–300 psi.  Operation range markings are placed on the cover glass, or  the face of the gauge, to indicate the safe range of oil pressure  for a given installation. A dual-type oil pressure gauge is available for use on  multiengine aircraft. The dual indicator contains two Bourdon  tubes, housed in a standard instrument case; one tube being  used for each engine. The connections extend from the back  of the case to each engine. There is one common movement  assembly, but the moving parts function independently. In  some installations, the line leading from the engine to the  pressure gauge is filled with light oil. Since the viscosity of this  oil does not vary much with changes in temperature, the gauge  responds better to changes in oil pressure. In time, engine oil  mixes with some of the light oil in the line to the transmitter;  during cold weather, the thicker mixture causes sluggish  instrument readings. To correct this condition, the gauge line  must be disconnected, drained, and refilled with light oil. The current trend is toward electrical transmitters and  indicators for oil and fuel pressure-indicating systems in all  aircraft. In this type of indicating system, the oil pressure  being measured is applied to the inlet port of the electrical  transmitter where it is conducted to a diaphragm assembly  Oil Pressure Gauge 6-9