Agitator motors

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ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
New install.

Agitators that are a motor with an impeller. Picture a two blade prop on a boat.
Started 4 today and the amp draw is in the 32 vs 19-21 amp expected. The guys did raise one up so it operated just below the surface of the water vs the bottom of the tank. 10 amps. Flow of the liquid would be horizontal in the direction of the impeller. Could the position in the tank relative to the bottom be the problem? To simple?

Motors, wiring, Hz, voltage all good.
 
bob

bob

Senior Member
Location
Alabama
Do you have the HP rating of the motor? When you raise the motor to the top of the tank, the load is not as great
as when it is deeper in the tank. It appears at first that the motor is under sized. Did the motor come as part of a
complete unit from the mfg?
 
T

topgone

Senior Member
ptonsparky said:
New install.

Agitators that are a motor with an impeller. Picture a two blade prop on a boat.
Started 4 today and the amp draw is in the 32 vs 19-21 amp expected. The guys did raise one up so it operated just below the surface of the water vs the bottom of the tank. 10 amps. Flow of the liquid would be horizontal in the direction of the impeller. Could the position in the tank relative to the bottom be the problem? To simple?

Motors, wiring, Hz, voltage all good.
Click to expand...

Most agitators come with gearboxes. Agitator load depends on the speed of the blades, the blade length/angle and the density of the fluid beeing stirred. Refer to manual if the specs fit your application. The gearbox ratio means a lot. Or, the agitator blades may have been angled wrong, hence a heavier load for the drive motor. Please see if you assembled the blades correctly. Also, sometimes the initial calculations fall short of actual conditions, i.e. the blades could be longer than desired or the fluid density is too much from initial assumptions during the design stage.
Perhaps, the easiest fix is to shorten the blades, like what most techs do with pump impellers overloading the pump drives. JM2C
 
Jraef

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Assuming that, as the electrician, you are not going to be questioning the design, component selection or make modifications to the equipment, there are a few more things you can do.

These are usually the equivalent of an axial flow pump, not a centrifugal pump. That just means the flow is going in the same direction as the shaft, but getting too close to the bottom RESTRICTS the flow because the fluid can't move into or away from the impellers fast enough. This ALSO means it is not necessarily a variable torque load. In a variable torque load, load decreases with flow, so if you were too close to the bottom of the tank, the flow would decrease and the motor would see LESS load. But on an axial flow system like many mixers, impeding the flow LOADS the motor more. So the first thing I would check is the design specs on how close to the bottom of the tank the blades were supposed to be. By the way, you will also see that in many cases, the mixer will be put in at an angle, that way you can't get to that point of restriction as easily.

Lightnin_ECL-209x300.jpg

The other thing, as mentioned, is the gear box. I know it sounds basic, but check to make sure the gearbox has oil in it. That's happened to me TWICE (you would think I would have learned the first time...). They are often shipped without oil, and a big tag on the gearbox telling you to add the oil. Guys tear those tags off and never read them.
 
mgookin

mgookin

Senior Member
Location
Fort Myers, FL
ptonsparky said:
New install.

Agitators that are a motor with an impeller. Picture a two blade prop on a boat.
Started 4 today and the amp draw is in the 32 vs 19-21 amp expected. The guys did raise one up so it operated just below the surface of the water vs the bottom of the tank. 10 amps. Flow of the liquid would be horizontal in the direction of the impeller. Could the position in the tank relative to the bottom be the problem? To simple?

Motors, wiring, Hz, voltage all good.
Click to expand...

When a liquid flows through a pipe, it flows in a vortex, and the greatest velocity occurs r/3 from the center (that's 1/3 of the radius). If you want more mixing and less drag on the motor, you may want to place the impeller in this location, if you can. Just my $0.02.
 
gadfly56

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
Did anyone confirm the gearing on these pumps to ensure they have the right RPM's? All things being equal, the load will increase as the cube of the RPM's. See here for a brief but excellent intro to mixing.
 
kwired

kwired

Electron manager
Location
NE Nebraska
JFletcher said:
Snot probably, tho even as much slang as we used at the plant, polymer was always polymer. With plug-ups of the jet-wet mixing systems and subsequent overflow everywhere, I'm sure we used "pita" more than a few times.
Click to expand...
Post 5 stated the application was for "manure slurry". I never been around such an application with this kind of material and heard someone say "it was plugged with polymer"

If I ever do it would about have to be a farmer that also has an engineering degree, and was never raised on the farm;)
 
H

Haji

Banned
Location
India
If a new motor is taking more than rated current, it is due to either wrong design, or LOW VOLTAGE for that particular motor.
 
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