Sportster Oil Pressure and Dynamics

[bustert]

hummmm???
even though water is a glass looks like a liquid, truth told there is some in the gas phase, just toooo small to see.
water makers use a vacuum and temperature to distill water. it is all about changing the vapor pressure point.
the sun evaporates water at ambient, but, it is solar energy that excites the molecule to the point of vapor pressure allowing a gaseous stage.
take the water pump on your chevy. the system pressurizes to 14psig but that is constant across the board. the pump moves water through the system and arrives at the suction about zero pressure, now if there is a restriction and the pump goes negative, the part of the water in gaseous phase will expand and can cause total loss of circulation.
cavitation and boiling are two diff animals.

Boiling is done by heating a reserved liquid whereas cavitation occurs because of reduction of pressure of a flowing liquid below its vapor pressure.

Collapsing of bubbles in case of Boiling doesn't make any damage to the container whereas bubble collapse in case of Cavitation causes significant damage to the moving parts of a machine .

what does that mean??? cavitation in an engine block carries energy and can erode the surrounding metal, waukesha had issues with this in some of the engines causing liner failure. you can boil water all day long in an engine and NO damage will be done, IF, the surrounding material can take the heat.

[Hippysmack]

Pump manufs and physics is telling me that you have to have both positive and negative on each side respectively in order for the pump to be efficient.
The pump design dictates what is required. Then you just give it what it needs.
There is also a practice of adding a pump upstream to keep positive pressured oil at the pump especially when the "oil level" is below the oil pump (industrial use).
The pump may be capable of sucking a golf ball through a garden hose as far as I know.
I could rig up a port on my old pump and see what vacuum it's running along with the feed hose at the same time.

We know now that gravity is somewhere less than a 1/4" psi.
The manometer readings on my bike initially were -28"wc at idle (just over -1 psi) and -1"wc at 5000 (-.036psi).
But those are just residual pressures.
In reality, piston action displaces the same volume that it sucks up inside the crankcase.
So there is potential for higher positive force on the scavenge port than there is on the feed hose.

[Hippysmack]

Bustert,
Uncle Bill (hydraulic engineer I once knew) put it like this.
Both cavitation and boiling are two peas of the same pod.
Both can occur due to a low pressure pulling vapors out of the liquid.
Cavitation is the one that explodes.
Boiling just sings.
He also said the heat generated from cavitation and affects thereof can cause boiling.
Now he was about 60 at the time, so was more laid back than I assume he was in his younger years.

But to freshen up, I did some looking around.
I had no idea there were so many interpretations of these things.
They all dance around each other featuring the heat from transfer or pressure drop causing boiling vapors.
And a pressure drop causing vapors, that when bubbles form, they manifest and explode when pressurized.
Whether bio-chemist, or nuclear engineer, physicist, hell others too.
Even they still argue the point between them.
But I think we got the just of it for our applications.

I rewrote part of post #134 so maybe it's not as confusing, probably needs something else but I know.

[Hippysmack]

He was pretty down to earth.
Drove me all over town showing me things he built.. talk your ear off.
I guess this thread reminds of some of those old times.
Old fart almost ran his car into a tree hitting the brakes to show me some 40 year old piping he conjured up.
Memories are a bad thing to lose.

[bustert]

uncle bill is incorrect

study the properties of a submarine propeller. why does it produce bubbles deep in the ocean?
pressure drop is large enough or temp is high enough, the drop may be enough to cause the water to flash to a vapor when the pressure falls below saturation pressure.
any vapor bubbles produced at the eye of the propeller are swept along the flukes by the flow of the water, when these vapor bubble reach a region where the pressure is greater than saturation, they abruptly collapse. why?? well the flukes are more loaded than the hub, right. this collapse is cavitation!! watch videos and see, there will be vapor bubbles coming more center to the hub. the newer propellers are an engineering feat, as they nearly suppress cavitation, reason why they need that??? well cavitation produces sound that can be picked up.

take a glass pot and fill it with water and slowly bring it to temperature and carefully observe the action!
first you will see tiny bubbles form, rise a short distance and disappear, also notice the sound it produces. this rapid production of vapor and collapse is cavitation.
as temperature rises and more vapor is produced, they have a tendency to combine to larger bubble and rise rapidly, but, the sound produced is NOT the sound of cavitation, that point is past! the sound you now hear is the large bubble breaking the surface of the water.
that large bubble contains very little energy since it is largely used in expansion. but the cavitation contains more energy and the sonic frequency is much higher. in the waukesha engine, under high loading, there was cavitation forming near the top of the liner due to high heat loads, this sonic energy was pitting the liner and eventually would fail causing liner leak. the liner was altered to high chromium surface in that area.
although they are related, they are NOT the same.