Sundyne LMV-311 overamping

[crivera]

I'm having problems with a LMV-311 drawing more power than the predicted performance curve says it should. At our current flowrate, we're reading a motor load approximately 15-20 hp above where the pump curve says it should be.
We are still within the limits of this motor, but with a pump conversion we want to install to increase the flowrate, we cannot use our current motor even though Sundyne says we can. We had the new conversion pieces installed and the predicted curve was within the limits of our pump, but on the test stand, we were running out of power on the motor.

Sundyne is stating that we have a problem with our motor, but both of our motors in the field are reading higher power than the pump curve is stating we should have. Our diffusers and diffuser covers are relatively clean and smooth. I had run across a posting at one time where someone talked about taking a skim cut on the diffuser when their pump was over amping and this cured their problem. Has anyone had experience with the pumps drawing more power than predicted?

The overamp situation was proved out by re-installing our original configuration and running it on the test stand with the same results we had in the field.

I think I can rule out a motor problem, because both of my pumps are behaving the same, I can't see that I have two motors that are each drawing 15-20 hp more than they should be. The motor did pull a reasonable amount of current when it was run solo.

Any help would be appreciated.

 

[itsmoked]

What's the motor Voltage and HP?

Certainly "shaving" the pump will reduce its current draw - along with its pressure, and flow.

How are you calculating the "power"? Are you mixing up kVA with kW?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[crivera]

We measured the power with a power condition monitor. I'm not sure of the details, but it measured voltage, power factor, and current through the 480V 3ph motor starter. It is a 125 hp motor. With that, the power was calculated and given to me.

As for the skim cut on the diffuser cover, that would increase the clearance between the back of the impeller and the diffuser cover (similar to the "dollar plate" on a regular horizontal pump). As Sundyne had said, the head developed and flow matched fairly well, but the horsepower delivered by the motor was high.

 

[JJPellin]

I have seen unusually high amps from a few Sundyne pumps. One set was model LMV-311. These pumps were in our Alky unit and had been designed for "clean" propane. However, we tend to get some acid carryover in this stream. The diffuser cover and diffuser would become rough and pitted from the acid corrosion. The amps would go up and the motors would trip off. We were able to take skim cuts on those parts to restore the surface finish and drop the amps back down with very little affect on capacity or pressure. The other pumps where we were tripping motors were VIP-801 canned motor pumps. We never got a satisfactory explanation for that problem. We upgraded to larger motors and eventually had to scrap the pumps and replace them with sealed pumps because of power, corrosion and heat problems. Sundynes are very sensitive to diffuser throat diameter, especially at the higher speeds and higher heads. On the highest energy designs, performance can be affected significantly by changing the throat by only a few thousandths of an inch. If it is a very high head very low flow design, excess flow through an internal cyclone separator can make a large affect on performance. We have another set of LMV-311's that had high internal seal flush flow that was causing a loss of performance and increase in power. Their numbering system for sizing the internal orifice is cryptic and confusing. I would make sure the diffuser throat size is correct, the internal orifice feeding the cyclone separator is correct (if equipped), ask them to verify the impeller pattern, inducer pattern and diffuser throat design.

I would ask them to verify the proper impeller diameter. They have one impeller design that uses a confusing part numbering system. Usually, the last 4 digits represent the impeller diameter. In this one design, the part number does not represent the diameter. Even Sundyne gets confused by this one. They once sold me the wrong diameter impeller three times before they got it right. They sometimes change the impeller diameter on the test stand based on meeting the guaranteed performance point. This change might not get documented in the Bill-of-Material or datasheet. They might have increased the diameter to meet the promised head, but not accounted for the extra power required.

I would verify the motor amps and voltage on all three legs. Your power meter could be reading only one phase and basing the results on the assumption that the others are the same. You could have an imbalance between the three phases that is not seen by the monitor.

Are you certain that your actual specific gravity matches the value used as the basis for the curve? If your product temperature is much lower than expected, the specific gravity could be too high. Have your product tested for specific gravity at the actual pumping temperature.


Johnny Pellin

 

[crivera]

The high amps/horsepower were seen with two sets of internals. The first set was the conversion which comprised of a new inducer, diffuser, diffuser cover, and impeller. The impeller was machined to the diameter required for the conversion and installed. When the shop tried to generate the test curve, they were showing signs that we would run out of horsepower before even reaching BEP where the predicted design still showed within the limitations of our motor. Since this test could not be taken all the way to the design point, a decision was made to re-install the original configuration and generate a test curve for it. The original pump parts were installed, and the test was repeated.

The surface of the old diffuser was not as smooth as the new parts from the conversion. The surface was actually coated with a fairly light surface rust with no noticable pitting or large rust particles. I did not get to view the old diffuser cover before it was installed.

I did not get to personally verify any internal dimensions with regard to the internal separator either. Upon testing the original configuration, again the head and flow matched up fairly well, but he horsepower was high. In our case the original configuration was still within our motor horsepower and may have been this way for a very long time.

For the power monitoring, in the field we monitored all three phases simultaneously and the amperage didn't vary too much between phases. In the shop I don't know if they looked at all phases. The specific gravity is actually just a little bit lower than the SG on the design sheet. The pumping temperature is approximately 100 Deg F, the same as the design conditions.

At the next opportunity I'll have to verify the internal orifice diameters. Another option I have is to eliminate the motor by having a dyno test to ensure my motor is capable of delivering the rated power as Sundyne keeps wanting to say I have motor problems.

Thanks,