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techtalk:ih:oil03 [2020/05/11 21:04] hippysmack [Oil Pump Cycle] |
techtalk:ih:oil03 [2020/11/07 04:16] hippysmack [Sub Documents] |
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| * [[techtalk:ref:oil06|Comparing the 77 Style Oil Pump to Newer Pumps]] | * [[techtalk:ref:oil06|Comparing the 77 Style Oil Pump to Newer Pumps]] | ||
| + | ====== Oil Pump Function ====== | ||
| + | |||
| + | The oil pump is a positive displacement unit. \\ | ||
| + | If you block the discharge flow path, discharge pressure will rise and literally approaches infinity until something fails. ((BuckIRyder of the XLFORUM http://xlforum.net/forums/showthread.php?t=730325&page=2)) \\ | ||
| + | It's non-regulated and delivers its entire volume of oil under pressure to the oil filter mount. \\ | ||
| + | However, don't take the term "positive displacement pump" literally. ((Dr Dick of the XLFORUM http://xlforum.net/forums/showthread.php?t=1429178&page=2)) \\ | ||
| + | Compared to a centrifigal pump, gear / gerotor type pumps use displacement to function. \\ | ||
| + | How positive it is depends on what it's pumping. \\ | ||
| + | |||
| + | The most 'positive' pump on our bikes may be the master cyl for the disc brakes. \\ | ||
| + | You pull the lever and it pumps real good, positive, unless there is air in the system. \\ | ||
| + | Then you still get the displacement but not the pressure because liquid is not compressable but air is. \\ | ||
| + | |||
| + | Gear / gerotor type pumps work by filling the spaces between the teeth with whatever it is that is being pumped (oil in our case). \\ | ||
| + | The oil in the tooth spaces gets squezed out of the spaces when the gear teeth mesh together (because a tooth is now in that space. \\ | ||
| + | But there is still a little space left at full mesh. \\ | ||
| + | Gearotor pumps have a smaller space at full mesh than gear pumps. \\ | ||
| + | |||
| + | Now when the mesh breaks, a void is created. Oil gets sucked into that void. \\ | ||
| + | Now what if air is in the spaces instead of oil? \\ | ||
| + | It gets sqeezed out also unless there is pressure (restriction) in the curcuit its trying to flow into. \\ | ||
| + | In that case, some air stays in the spaces and gets compressed in the small space remaining as the teeth mesh. \\ | ||
| + | When the teeth unmesh, air expands (refilling void that should be getting oil sucked into it. \\ | ||
| + | The pump can't make enough pressure to overcome the exit restriction. \\ | ||
| + | Then there is no flow and no ability to reprime itself since. \\ | ||
| + | (it's not making enough suction due to the expansion of the compressed air refilling the void that the oil should be filling) \\ | ||
| + | |||
| + | Eventually the pressure in the return line gets released. \\ | ||
| + | While this is happening oil is building up in the pickup sump and waiting for the return side to come back online. \\ | ||
| + | The supply pump is still pumping while the return is toggling from air locked to primed and pumping. \\ | ||
| + | |||
| + | Think about what state the return oil is in as it collects in the return pickup cavity. It's just been thru a 60 cycle blender. \\ | ||
| + | Our bikes live with that every mile they travel with lots of air whipped into every drop of return oil. \\ | ||
| + | Restrictions in the return side of the pump will lead to a more sustained oil level in the crankcase sump. \\ | ||
| + | (large enough to reduce outflow from the engine to a volume less than the supply pump is feeding the engine) \\ | ||
| + | |||
| + | This is a condition known as wetsumping. \\ | ||
| + | Read more about [[techtalk:ref:oil10|wetsumping]] in the REF section of the Sportsterpedia. \\ | ||
| ===== Production Oil Pumps ===== | ===== Production Oil Pumps ===== | ||
