I just finished R-2800: P&W's Dependable Masterpiece and noticed there's no mention of a pump for crankcase ventilation. Is this handled by the oil scavenge pumps?
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asked May 24, 2019 at 23:33
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$\begingroup$ By ventilation do you actually mean return of oil? When I see that word I think of a crankcase breather to let gasses out. If you mean oil, it will certainly have a scavenge pump or pumps, as with any dry sump engine. $\endgroup$– John KMay 25, 2019 at 4:05
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$\begingroup$ @JohnK no I'm speaking from life experience. In car engines, there's always such a pump because combustion gas would go over the piston rings and accumulate in crankcase if not constantly sucked off. It's usually a positive displacement type of pump. $\endgroup$– Meatball PrincessMay 25, 2019 at 5:12
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2 Answers
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The radials were virtually all dry sump systems. Within a dry sump system is an air-oil separator as well as overboard breathers for the crankcase and dry sump oil tank.
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In a car the combustion gasses that blow past the piston rings are sucked out by a line connecting the crackcase to the intake manifold by a check valve (the PCV valve). The suction "pump" is from the low pressure in the intake manifold. Cars before the PCV valve (developed in the 50s) just vented the crankcase gasses overboard through a hose. Aircraft engines, including the big radials and the Lycoming engine on my own plane, do the same.
Positive crankcase ventilation was probably the first pollution control device developed for cars. Piston aircraft engines have never used pollution control devices. They still use gasoline with lead in it.
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1$\begingroup$ LOL yes. I was shopping for PVC pipe yesterday... $\endgroup$– John KMay 26, 2019 at 2:27