Flow rate into parts

[Silver]

I have read over and over that in a 'displacement' oil pump, flow is equal across viscosities.

But, concerning the flow of oil in between tightly fitting bearings, parts, etc inside the engine, a thinner oil would flow into those tight spots quicker, wouldn't it?

Particularly, if some areas are not getting oil as a direct influence of pressure, then gravity alone is carrying the oil into the part, correct? If that is correct, the speed at which oil reaches these parts not in the direct path of the pressure would be dependent on the oil's 'resistance to flow' (viscosity) correct?

This scenario where a part depends on gravity alone to receive oil may not exist in a practical sense. I don't know, just putting this out there.

 

[OVERKILL]

I have read over and over that in a 'displacement' oil pump, flow is equal across viscosities.

But, concerning the flow of oil in between tightly fitting bearings, parts, etc inside the engine, a thinner oil would flow into those tight spots quicker, wouldn't it?

Particularly, if some areas are not getting oil as a direct influence of pressure, then gravity alone is carrying the oil into the part, correct? If that is correct, the speed at which oil reaches these parts not in the direct path of the pressure would be dependent on the oil's 'resistance to flow' (viscosity) correct?

This scenario where a part depends on gravity alone to receive oil may not exist in a practical sense. I don't know, just putting this out there.

As long as the pump isn't on the relief, the flow rate of the oil is the same. At higher temps, again, assuming no relief operation, a thinner oil will "slip" by the pump more than a slightly more viscous one so in fact you'd get less flow; less volume, per revolution due to that phenomenon.

There are very few, if any, areas in your typical engine that are lubricated by gravity. Probably the biggest impact a super thick lube would have is on the "sling" from the crank/rod interface that lubes the cylinder walls. But, the shearing heat and pressure within the bearings means that this viscosity is rapidly reduced resulting in a proper sling pattern for lubrication.

 

[ABN_CBT_ENGR]

At higher temps, again, assuming no relief operation, a thinner oil will "slip" by the pump more than a slightly more viscous one so in fact you'd get less flow; less volume, per revolution due to that phenomenon.

Respectfully that could only happen if the PD pump was mechanically defective or spec'd wrong (in terms of tolerances) for the fluid being pumped. They don't recirc like a regular centrifugal.

 

[ABN_CBT_ENGR]

But, concerning the flow of oil in between tightly fitting bearings, parts, etc inside the engine, a thinner oil would flow into those tight spots quicker, wouldn't it?

No, see Bernoulli and Poisson

The velocity would be faster due to the reduction of space but that compensates by the volume.

Like a garden hose filling a bucket

spray with a nozzle or let the hose run, velocities are different but flow is the same

Gravity is a whole different animal and the pump doesn't control gravity.

 

[CR94]

Respectfully that could only happen if the PD pump was mechanically defective or spec'd wrong ...

You overlooked Overkill's word "slightly." Against pressure, there's normally a difference between theoretical and actual flow per revolution, although that difference with a healthy pump is too small to be significant compared to "flow" confusion typical of many BitOGers.

 

[ka9mnx]

I would say a lighter oil will flow easier but not quicker. That is, less drag (energy) required by the oil pump to flow the oil.

 

[OVERKILL]

Respectfully that could only happen if the PD pump was mechanically defective or spec'd wrong (in terms of tolerances) for the fluid being pumped. They don't recirc like a regular centrifugal.

I've seen it referred to as "pump slip" and it's due to the less than perfect tolerances and thus overly generous clearances in your typical mass produced oil pump. Again, we aren't talking textbook perfection but rather the realities of producing millions of something that's "good enough" for your average car engine. There was a whole paper on it discussed at one point on here, was quite interesting.

 

[ABN_CBT_ENGR]

I've seen it referred to as "pump slip" and it's due to the less than perfect tolerances and thus overly generous clearances in your typical mass produced oil pump. Again, we aren't talking textbook perfection but rather the realities of producing millions of something that's "good enough" for your average car engine. There was a whole paper on it discussed at one point on here, was quite interesting.

You are correct and the line between design slip ( nothing being perfect) and a mechanical malfunction is vary vague and undefined- no argument there and every design engineer fully understands this.

That being said, "slippage" defined as the percentage of inefficiency/loss cannot be ascribed as fluid transfer from the high pressure side to the low pressure side, that's a malfunction, not a loss of efficiency. No other way it can be stated.

The point I was referring to relative to your post is the malfunction part ( due to design and application issues) not normal loss of efficiency.

Otherwise, it seems you and I are pretty much parallel on the point at hand with little difference between what we are saying.

 

[ABN_CBT_ENGR]

You overlooked Overkill's word "slightly." Against pressure, there's normally a difference between theoretical and actual flow per revolution, although that difference with a healthy pump is too small to be significant compared to "flow" confusion typical of many BitOGers.

Discounting slip/efficiency and assuming a properly rated pump- there wont be.

If it does happen then there's a problem with the pump or the rated application.

 

[CR94]

So discounting "slip," there won't be "slip"? That's helpful.

 

[ABN_CBT_ENGR]

So discounting "slip," there won't be "slip"? That's helpful.

No, in layman's terms "slip" has no bearing on the pumps output because its factored in thus "non existent" in terms of the subject matter in question. All pumps BEP is about 80% so no amount of "slip" will ever touch that.

 

[Bryanccfshr]

I don’t worry about pumping losses the differences are not significant. . another known loss is windage loss when the oil drops into the moving crank, but many Engine designs have windage trays and two part oil pans to help eliminate windage loss.

 

[barryh]

As long as the pump isn't on the relief, the flow rate of the oil is the same.

What is the normal design philosophy for relief operation. I expect they flow the whole time when the oil is cold.

I know of one application where the relief is more or less permanently flowing oil hot or cold, in fact the cam chain lubrication depends that it does. Only at hot idle does the relief valve not flow oil. In this case oil flow rate is determined by viscosity for a high percentage of the time.

I assume this is not a typical approach.

 

[ZeeOSix]

But, concerning the flow of oil in between tightly fitting bearings, parts, etc inside the engine, a thinner oil would flow into those tight spots quicker, wouldn't it? Particularly, if some areas are not getting oil as a direct influence of pressure, then gravity alone is carrying the oil into the part, correct?

No, see Bernoulli and Poisson

The velocity would be faster due to the reduction of space but that compensates by the volume.

Like a garden hose filling a bucket

spray with a nozzle or let the hose run, velocities are different but flow is the same

Gravity is a whole different animal and the pump doesn't control gravity.

We was specifically talking about parts that are splash lubed or gravity flow lubed, not PD pump pressurized.

 

[ABN_CBT_ENGR]

We was specifically talking about parts that are splash lubed or gravity flow lubed, not PD pump pressurized.

No, "we" wasn't

 

[ZeeOSix]

No, "we" wasn't

The OP and We ... but not you.

 

[ABN_CBT_ENGR]

The OP and We ... not you.

Actually it was broad based and not restricted to any one item or component but that goes back to your other areas we have previously identified

 

[ZeeOSix]

Broad based ... yeah, that's it. What about that "whole different animal" that's not controlled by the PD pump?

 

[4WD]

So discounting "slip," there won't be "slip"? That's helpful.

Resistance to flow (residual pressure)
Inside diameter, Rate (Q), Length, Density, Viscosity (shear stress)
There is not much hydrostatic pressure in an engine since the vertical height is limited … so gravity feed is slow.
(that is mainly post end user return)