Oil Pump Dyno

[Joe-JDC]

My first concern was the pressure would actually drop with the larger tubing.  Glad to see it did not.  Great information.  Joe-JDC

[machoneman]

94/92 = 2 psi difference = 2.17% difference, likely within a 98% confidence interval. I'd ignore this minimal difference or run the test 2 more times....and average all 3. If so, I'll bet the difference would drop to maybe 1 psi, maybe even less. JMO.

[Nightmist66]

My first concern was the pressure would actually drop with the larger tubing.  Glad to see it did not.  Great information.  Joe-JDC

Why would it drop? I'm not as sharp as most guys here, but it seems like this is a simple case of supply vs demand. Especially at higher pump speeds, if the pump is meeting a restriction on the suction side(such as a small pickup tube), then it would seem as a larger diameter pickup would be beneficial. Can the pickup tube be too large? Like 3/4"? The inlet to the pump should be suited to match the upsizing I would assume, or there is still a bottleneck. I would think unless you start sucking air at some point, the more available(oil through pickup), the better. This may not always be needed though, as with milder builds/lower rpm/thinner oils. Wouldn't an analogy of trying to suck air through a coffee stirrer and then again through a regular straw be the same principal?

[runthatjunk]

 For some reason this time the bypass valve decided to open at 94 psi instead of 92 psi.  I can't explain that with the changing of the pickup!
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If the pump is bypassing internally wouldn't the smaller pickup showing a restriction cause a bit of pull on the back side of relief valve possibly?

[WConley]

For some reason this time the bypass valve decided to open at 94 psi instead of 92 psi.  I can't explain that with the changing of the pickup!
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If the pump is bypassing internally wouldn't the smaller pickup showing a restriction cause a bit of pull on the back side of relief valve possibly?

I think the rear of the bypass valve is not exposed to suction-side pressure.  It just seems to be a closed chamber with a spring and cup plug.  If that's the case, the suction pressure would have little effect.

[winr1]

Would like to see what what would happen if the oil supply to the pump was above the pump



Ricky.

[WConley]

Would like to see what what would happen if the oil supply to the pump was above the pump



Ricky.

Probably not much, except that the pump would stay primed and pressure would come up much faster on startup.  In order to add 1 psi to the static output pressure, the oil supply would have to be about 30 inches above the pump.  (That's from the density of a column of oil - gauge pressure at the bottom of the column.)

In reality a lot of the pressure loss is from pipe flow friction in the passages.  This gets worse as the flow rate goes up.

[427John]

Would like to see what what would happen if the oil supply to the pump was above the pump



Ricky.

NPSH doesn't affect positive displacement pumps nearly as much as it does centrifugal pumps.

[XR7]

Have you run the pump up to 8500? Just curious, as there are guys that take them that high, will it just flat-line or will it start to drop or dip at some point higher than shown (7500)?

[WConley]

Have you run the pump up to 8500? Just curious, as there are guys that take them that high, will it just flat-line or will it start to drop or dip at some point higher than shown (7500)?

I think the M-57 B will keep going for a bit, while the M-57 HV will just keep bypassing (flow slowly dropping off as it aerates the oil).

Next time I get a chance I'll pull the M-57 B up to 8,500.  It should do fine up there.

[pbf777]

Would like to see what what would happen if the oil supply to the pump was above the pump
Ricky.

Probably not much,

     The comparison would be as to the fluid level of the sump to the pump position; in the typical Ford V8 with the oil pump submerged in the sump the pump receives oil readily, and generally remains primed for restarts, but removing the pump from this position such as higher timing cover or external block mountings then the changes in the relation of the reservoir fluid level may have dramatic effects.     

     A time ago we did some testing work for an oil pump manufacture who's product was not accomplishing that which they claimed; we were at a loggerhead as our definitive results as mounted to the engine just were not as their "engineers" had reaped from their test stand!  In passing I asked: so, where is the oil reservoir in relation to the pump mounting on your testing fixture?  Answer: several feet above the pump, by this won't make any difference as this is a positive displacement pump design.  I said well, why don't you move the oil volume down to the level of the pump, and with further testing even below as is required in some installations and watch what happens!  Their engineer called me back and stated that with those changes their results mirrored ours! Sorry.     

     Scott.

[WConley]

I would say that pump was having trouble keeping a prime.  Perhaps a leak in the pickup path somewhere?  Millions of production geroter pumps run just fine sitting above the oil bath.  On my test rig, the pumps are not in the oil bath and they pull up pressure quickly.

[pbf777]

I would say that pump was having trouble keeping a prime.  Perhaps a leak in the pickup path somewhere?

    If this is response to my previous post?.................then nope!

    We also did repeated testing of the "ideal" diameter for this pick-up path, and note that it must be established just exactly how much oil is being distributed but for say something around eight gallons per minute as this is an approachable sum for a somewhat "lose" big block, and finding that 1/2" I.D. sufficient for up to say 8" approx., then 5/8" for longer distances which should cover most in the pan installations, for external pump installations -12 hose for reasonable runs in the engine compartment with no real benefit for -16 hose unless running the length of the chassis distances (though we have chosen otherwise in some instances), say dry-sump reservoir mounted in the trunk with perhaps limited drop in elevation.  But, definitely avoid having to "lift" the oil to the pump inlet!     

    And, if pumping in excess of say eight gallons or more per minute, those little boxes with the perforated steel sheet "screen" mounted on the end of the P.U. tubes really.......... "sucks"!   

    Also for many, one needs to reconsider just how close one thinks the P.U. inlet should be to the bottom of the pan.        

    Remember, one does want to avoid creating an excessive pressure drop in this inlet path, even if the pump is able to maintain the outlet sum, as there will be a loss in the quality of the delivery.

    And also, there are many other variables not present within a test stand versus mounted to functioning engine that at times muddies the water so to speak, much as with air flow numbers from a flow bench versus which cylinder head that actually made more power.  This doesn't negate the observation and value of the endeavor, and I do really appreciate this thread looking forward to the observations and discoveries being presented thru what many might not realize is a great sum of effort by Mr. Conley, but still, it may prove frustrating when one experience doesn't mirror another other.     

     Scott.

[427John]

While NPSH(oil above suction of the pump) shouldn't have a major effect on the positive displacement pump performance it will minimize if not eliminate the effect of any air leakage into the suction side of the pump.The typical mass produced bolt on oil pickup tube with thin paper gasket and sweated on flange hardly qualify as the most reliable method of air tight joint,while they obviously work well enough for the majority of rigs out there,every time I installed one I wondered about how much air leaks in there.The more modern engine oil systems with their o-ring sealed joints appear that they would be better,but then how much cost does that add.While minor leaks on the pressure side just eats into the excess capacity of the pump air into the suction can have a major effect on pump performance.

[WConley]

While NPSH(oil above suction of the pump) shouldn't have a major effect on the positive displacement pump performance it will minimize if not eliminate the effect of any air leakage into the suction side of the pump...

This was my point.  If a positive displacement pump is seeing strong output changes from a few inches variation in the input head pressure, there's a problem.  That problem typically involves input side air leakage.

Think about it.  The pump is an inch above the oil bath, and is not delivering as expected.  You move the pump down an inch and suddenly all is well.  If that inch of suction-side static pressure head made the difference, then moving the pump up another inch away from the oil would make it twice as bad.  My years of experience (and graduate level study of hydraulics) do not support this.  The only difference is that the inlet side is submerged and can no longer leak.

Now if we're talking about non-positive displacement pumps, all bets are off.  They will be affected by changes in inlet head pressure.  In fact, the definition of a true positive displacement pump is one where flow is independent of pressure.

That's the key term.  Flow is independent of pressure.  A geroter pump is almost a true positive displacement pump, because there is slight leakage.  For our purposes and at the speeds we run our pumps, they can be treated as truly positive displacement.  It takes large pressure changes (many psi) to have a noticeable effect on flow.  I have seen this on my test rig when I adjust the orifice valve.  A slight change in inlet side static pressure head (<< 1 psi) will not create a measurable change in output.  Of course, you need to have sufficient flow capacity to the inlet (pipe size).