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Effect of 90-Degree Fitting on Lube Oil Flow at Different Speeds
2

Effect of 90-Degree Fitting on Lube Oil Flow at Different Speeds

Effect of 90-Degree Fitting on Lube Oil Flow at Different Speeds

(OP)
I am measuring a gear pump's suction pressure at different speeds (500, 1000, 2000, and 3000 RPM) using SAE 30 lube oil in ambient conditions.  Comparing the results between the initial set-up (bended tubes) and putting a plugged T-fitting on the suction side (see TFittingSetUp.JPG) to gauge the effect of one 90 degree elbow, I noticed that at 500, 1000, and 2000 RPM the set-up with the T-fitting resulted in a suction pressure rise of 56%.  But at 3000 RPM the suction pressure rose only 15% from 9.6 psi to 11.1 psi.   What would cause the much lower rate of increase at 3000 RPM?

RE: Effect of 90-Degree Fitting on Lube Oil Flow at Different Speeds

Tabulated data of RPM and Suction Pressure or Suction Pressure Drop would be useful.  I'm not sure what you are comparing to what?

Good luck,
Latexman

RE: Effect of 90-Degree Fitting on Lube Oil Flow at Different Speeds

Maybe because it's well lubricated  smile2

RE: Effect of 90-Degree Fitting on Lube Oil Flow at Different Speeds

(OP)
Speed   Base    T-Fitting
RPM    psi    psi
500    1.7    2.7
1000    3.2    4.9
2000    6.3    9.8
3000    9.6    11.1

Attached is an image of the "base" set-up to complement the previous image.  I hope that helps better explain what I am comparing.
 

RE: Effect of 90-Degree Fitting on Lube Oil Flow at Different Speeds

What was the flow rate at the various speeds, did the flow increase in protortion to the speed increases.

RE: Effect of 90-Degree Fitting on Lube Oil Flow at Different Speeds

I'm not exactly sure what the data you have presented are or where you are measuring your pressures.  But one of your gauges is 0-400 psig.  If this is the gauge you are using for these pressures then your data is worthless.  If you are using the other gauge (which is a vacuum gauge) then please state the units of your pressure data.

RE: Effect of 90-Degree Fitting on Lube Oil Flow at Different Speeds

I assume the psi figures are pressure drops in the suction line.  Correct me if I'm wrong.  Have you thrown the data against the wall and looked at it?  Graph it with Excel or JMP or some other software.  Do a power law trend line, because pressure drop is usually proportional to flow rate (or RPM in a PD pump) squared.  The trends of the two data sets are similar to each other, but not what I would have expected.  Cavitation?  Pump slippage or internal recycling?  Lines not hydraulically full?  All rthings to look for.

Good luck,
Latexman

RE: Effect of 90-Degree Fitting on Lube Oil Flow at Different Speeds

(OP)
These are the raw data from vacuum gauge readings.

Speed    Base    T-Fitting
RPM    in Hg    in Hg
500    3.5    5.5
1000    6.5    10.0
2000    12.8    20.0
3000    19.5    22.5




 

RE: Effect of 90-Degree Fitting on Lube Oil Flow at Different Speeds

The vacuum gauge readings are useless without further information such as flows or power readings, if you want an answer you need to give meaningful information.  

RE: Effect of 90-Degree Fitting on Lube Oil Flow at Different Speeds

Makes perfect sense to me.

At 3000 rpm you may be right at or close to a choked flow condition with the t-fitting (which is more restrictive that your smooth transition setup), at which point the fluid can move no faster.

With the t-fitting set-up, if you begin to hear a noisy, rumbling sound from the pump, then it may cavitating, which would signify that the fluid flow is becoming "choked".

At some higher rpm and flow rate, the tubing will also become choked as well.

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