Here is a recent paper on a rig that was built by some researchers in India. I was researching this subject and found it.

http://ijates.com/images/short_pdf/1425886013_584.pdf

Kinda fun to read. The rig is crude, but they did make it work. Can't imagine the oil they were pumping. Nasty stuff.

What's really interesting is they referenced a us patent 6123533.

Cavitation-free gear pump - Patent # 6123533 - PatentGenius

The inventor speaks to high speed cavitation in the suction side gear mesh. Caused by the teeth in the center opening appart and creating a sudden increase in volume that has to be filled or cavitation can occur.

If I thought about the high speed filling characteristic of the mesh, losses on the intake could affect the risk of local cavitation. Which could reduce the volumetric efficiency.

It is possible that what people stumbled across was the high rpm filling characteristics were improved when more attention was paid to the local transitions in the inlet

That might explain the physics, and the reasons why pump flow could increase with some better inlet porting.

This video is cool
http://youtu.be/hh7CaWd8Ou0

Shows the cavitation in the expanding gear mesh.

Forget the empirical formula, cavitation, pressure drop, parasitic loss, etc. Just share with us how you bench test a 911 oil pump. Thanks. I think the answer is without these parameters they don't really have any means to test the pump.


regards

In an earlier post, I stated that we test the oil pumps on an engine lathe with a vacuum gauge. The next time we test a pump I'll try to take pictures so everyone can see how we do it.

Henry - can you share what vacuum you consider adequate?

Test oil weight? Or can you just fix the gauge to an inlet, spin the lathe, and measure? Less mess, and comparing new pumps to used ones would provide a baseline even though air's viscosity is nowhere near oil's?

The reason that it is common practice in the Automotive maintenance world 'inspect' pumps rather than try to test them is that you need to replicate all of the conditions that the pump experiences to gain a genuine result.

If the pump body is not at its operating temperature then clearances will be reduced and both cavitation and spill measurements will be inaccurate.

If the oil isn't heated to the correct operating temperature the cavitation and spill characteristics will be inaccurate. It would be possible to simulate this a 'test fluid' of the correct viscosity.

If the outlet pressure is wrong then the spill characteristics will be wrong.

As a simple example 'spill' for a given clearance and oil viscosity is directly proportional to pressure and this will affect flow.

If the outlet pressure is zero then spill will tend zero even if lateral clearance is excessive.

If you test a pump under zero outlet pressure conditions you will never obtain a meaningful baseline as a 'bad' pump will flow virtually as well as a 'good' pump.

In the last few years the frequency with which new pumps are tested has fallen due to improved component inspection and a reduction in the dimensional variation of individual parts.

Test set up.......
 

Henry,

I acknowledged your post earlier and gave me an idea how to make a suitable set up. It would be beneficial and helpful for DIYers to be guided in doing such test. For example, since I don't have a lathe machine, I could use a variable motor to set the RPM. What grade of oil and temperature to use? What delivery pressure to expect versus RPM. I am certain that you will share your experience with us. Love to see some demo pictures. Thanks.

Tony

At this point, "specifics" tend to get accusations of lying and that, quite frankly gets tedious.
I will offer these observations and be done with this conversation.
Over the years we have seen marked (observable) improvement in pump output by performing some simple modifications to the internal port shapes.
Second, and this one speaks directly to the concerns of the DIY builder: I have never seen a 911 oil pump that failed to perform as designed that wasn't physically damaged. IE: even a worn pump will out perform the needs of a stock or close to stock engine. If the engine requires an increased flow (trying to create crankcase vacuum, moving more oil through a cooler for race application, or higher pressures to compensate for bearing clearance also in race application) the only cure for that is a larger (turbo, 996TT or GT3) pump.
Third, mag case pumps seem to perform less efficiently when hot due (I assume because I have no empirical data) to excessive housing expansion but when modified even those pumps perform adequately in a sub 200hp engine.

Pressure will vary in a linear manner with speed until the pressure reaches a set value or until the pressure differential across the pumps starts to cause sufficient spill so that the output of the pumps equals the spill rate and an equilibrium pressure is produced.

If this pressure is lower than the set pressure required by the engine then the pumps would be quite poor as clearance would most likely be too high.

If you test the pump with the grade of oil you use on the engine at 90 degC then the pump will arrive at the correct temperature and all of the other required conditions will be met.

If you measure the flow at zero pressure and then flow at different pressures you will be able to see the impact of clearance and determine the 'spill' curve for the pump.

Spill should be proportional to the cube of the clearance and linear with differential pressure.

Determining cavitation is much more complex and the most appropriate way is to use a rotating torque meter and the pump cavitates there will be a very observable frequency modulation on the mean torque signal.

Engine oil at a typical temperature of 90degC has a bulk modulus of around 1.5 x 10^9 Pa which means at 65 psi the volume will only reduce by around 0.03% so you can ignore compressibility.

Measuring the scavenge section is more straightfoward as you can only measure suction pressure. The pump develops no real positive pressure in this condition so spill effects become irrelevant and providing bearings are in good order and that the pump is therefore rotordynamically sound all should be OK.

You could measure the flow of this section of the pump with 'solid' oil but there is no real point in doing this work.