How does an oil pump deal with reduced flow?

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Can someone with knowledge on fluid dynamics educate me on this? Let's say the size of the mouth on an oil pickup was reduced by about 50% due to an obstruction, the oil pump's rotation is usually linked to the rotation of the crankshaft, with one revolution of the oil pump's internals, how does it cope with the obstruction?

It can't create air inside the pump if there's no air being sucked in, so what's to replace the 50% loss in the mouth? Does the pump just work harder, power in the engine is lost and the flow through the remaining 50% increases in pressure or something? If the obstruction was 100% and the engine was forcing the pump to pump, this should cause a vacuum and something would have to give right?

Basically how big of a deal is it if the opening on an oil pickup is obstructed? I'm referring to the oil pickup design where there's a sheet metal casing with an opening and a strainer inside the sheet metal casing, not the kind where the strainer is fully exposed.
 
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I presume the pickup and tube heading into the pump is designed to ensure laminar (smooth) flow. I also assume its designed such that if the screen is partially plugged there still isn't enough pressure drop across the screen for the flow to still flow in a laminar fashion - ie smooth flowlines.

So the answer is I guess it depends. If you change it enough to be turbulent you will end up with oil that froths and possibly cavitation in the pump - both are very bad.

Why do you ask?
 
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If an amply sized intake becomes only 50% blocked, nothing will happen except slightly increased pressure drop through it. The flow rate would not change significantly. However, if the intake is already significantly clogged, then you might have a problem.

The 50% blockage would be more likely to cause trouble if the temperature is so low that the oil is barely pumpable.
 
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MolaKule

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Can someone with knowledge on fluid dynamics educate me on this? Let's say the size of the mouth on an oil pickup was reduced by about 50% due to an obstruction, the oil pump's rotation is usually linked to the rotation of the crankshaft, with one revolution of the oil pump's internals, how does it cope with the obstruction?

It can't create air inside the pump if there's no air being sucked in, so what's to replace the 50% loss in the mouth? Does the pump just work harder, power in the engine is lost and the flow through the remaining 50% increases in pressure or something? If the obstruction was 100% and the engine was forcing the pump to pump, this should cause a vacuum and something would have to give right?

Basically how big of a deal is it if the opening on an oil pickup is obstructed? I'm referring to the oil pickup design where there's a sheet metal casing with an opening and a strainer inside the sheet metal casing, not the kind where the strainer is fully exposed.
Sounds as if you might have sucked a piece of metal into the screen, such as a bolt?

@CR94 and others have given some good responses: If an amply sized intake becomes only 50% blocked, nothing will happen except slightly increased pressure drop through it. The flow rate would not change significantly. However, if the intake is already significantly clogged, then you might have a problem.

The 50% blockage would be more likely to cause trouble if the temperature is so low that the oil is barely pumpable.


An obstruction would be similar to a converging (narrowing) channel which will cause an increase in velocity but at the same time will cause a decrease in the pressure.

In the case of the intake, the oil will try to flow faster around the obstruction but at the same time (and as CR94 stated) the pressure will drop.

If this is in an engine and you have an oil pressure gauge, then it should show an upstream pressure drop from nominal pressure.
 

Omahaug

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Thanks for all the responses!

The backstory on this, I recently (like a week ago) replaced a dented oil pan, the dent had clipped half the pickup opening which basically pushed it in a little, the end result is the pickup mouth is now about 50% narrower than it should be (based on reference pictures).

I only realized this after putting the new pan on. I was mulling over whether to pull the new pan and new RTV off but based on the responses I've now resigned myself to doing it (what a pain in the ***). I'm going to pull the pan and put my finger into the sheet metal dome around the pickup and pull the pushed in part back out (the metal is thin and easy to bend). Going to cost me 5 more quarts of oil and I hope I don't damage the new pan taking it off lol.

I'm not replacing the pickup because the "damage" is minor, it's attached using two fasteners and sealed with liquid gasket, don't want to upset any of that...

This is what the pickup looks like (not mine, a reference picture):
1667802425350.jpg
 
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