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Fuel Pressure Drop with ASA Crankcase Vacuum Kit

avrojockey

avrojockey

Well Known Member
Patron
I'm getting a ~1 psi drop in fuel pressure after installing Anti-Splat Aero Vacuum kit on oil separator. Seems like this is normal since the pump diaphragm is exposed to crankcase atmosphere.

My question is how low is too low? Lycoming manual says 0.5 psi minimum at carb and I'm at ~2.0 in cruise before the red cube...which drops it a little more (0.5 psi at most)

Good news...I defiantly gained (as Charlie Berens would say) a-couple-two-tree knots

Merry Christmas!
 
Last edited:
Did ya really gain a couple two tree knots? Yeah no? Or no yeah? Oh and tell your folks I says hi.
 
So I'm thinking about this a little more...pressure is resistance to flow...so what is actually happening is the crankcase vacuum is reducing the flow rate of the engine driven pump since the restrictions down-stream haven't changed. I guess what Lycoming is saying with 0.5 psi minimum for a carb, that any flow rate that produces minimal pressure is adequate for the power plants need at maximum power
 
Great video! Totally explains why increased crankcase vacuum on the diaphragm counteracts the spring's action, which is what actuates the pumping of the diaphragm.
 
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