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Pump motor still hot while the pump in right head range

04/23/2022 5:16 PM

We use water pump (stainless steel case & Impeller) to handle edible oil, from storage tank to buffer tank, we calculate the available head is around 20m head, the pump head range min 10m max 35m, we install pressure gauge, reading is 24m (2.4bar) which is efficient point in pump curve, the rated current is 4.4A

The problem is, pump tripped out because of over current which is 4.55, 4.6, 4.8 A, we contact the manufacturer he advice to increase the overload 5%, the pump now not tripped out, but the current reading still high, and the motor is hot which is will lead to motor damage.

we don't know where is the problem since there is no process problem, is it application problem when we use water pump in edible oil application?

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#1

Re: Pump motor still hot while the pump in right head range

04/23/2022 6:47 PM

"Would water require less energy to pump than oil?

This question actually gets to the heart of why people in the field of fluid mechanics rely so heavily on non-dimensional numbers. It really depends on which is more important in the flow you're considering, viscosity or density (which obviously leads to the Reynold's number). Which fluid property dominates will depend on how fast the fluid is moving. If it's moving relatively quickly (turbulent flow) then the density forces will dominate and oil would require less energy to pump than water. If it's moving relatively slowly (laminar flow) then viscous forces dominate (making the friction factor much higher) and water is actually easier to pump."

When we are investigating the type of flow in a pipe, we use the formula: “Re = QDH/νΑ” where “Q” is the fluid flow rate, “DH” is the hydraulic diameter, “ν” is the kinematic viscosity, and “A” is the pipe cross-sectional area. The hydraulic diameter is determined with: “DH = 4A/P” where “P” is the “wetted perimeter”, or the area that contacts the fluid flow.

https://www.quora.com/What-is-the-difference-between-an-oil-pump-and-a-water-pump

https://www.quora.com/Can-I-use-a-domestic-water-pump-2-kW-in-pumping-oil-or-do-I-have-to-use-a-special-pump-for-oil

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#2
In reply to #1

Re: Pump motor still hot while the pump in right head range

04/23/2022 11:57 PM
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#3

Re: Pump motor still hot while the pump in right head range

04/24/2022 2:10 PM

Two things come to mind. The viscosity of the oil may be higher than the viscosity of water, so the pump has to work harder. Another factor is that water is a much more efficient coolant than oil.

https://nrs.blob.core.windows.net/pdfs/nrspdf-5ebdd55a-69c6-4800-b26e-09add3cb3a9a.pdf

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#4

Re: Pump motor still hot while the pump in right head range

04/24/2022 2:54 PM

Has <…hot…> been discussed with the motor manufacturer? What was the outcome?

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#5

Re: Pump motor still hot while the pump in right head range

04/24/2022 6:15 PM

Why, oh why do you continue to use a tool not designed for your job. Edible oil pumps are designed to handle the relatively wide viscosities and density changes that happen from changes in temperature and product. (They're also designed to keep edible products edible.) In contrast, water has a higher density than oil but a much lower viscosity than many oils.

Get the right tool for the job.

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#6
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Re: Pump motor still hot while the pump in right head range

04/24/2022 9:46 PM
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#7

Re: Pump motor still hot while the pump in right head range

04/25/2022 5:19 AM

I would be much more concerned about contamination of the edible oil than the pump over heating. Water pumps are not designed to handle food products. There are cavities behind the impeller where old oil will lodge with the possibility of a build up of bacteria. Repeated heating of this old oil will break it down into fats which will accelerate the contamination problem. Based on the rated current you have a 2.2 Kw motor which can only drive a relatively small pump. Therefore the cost of replacing the pump with a food rated one that is designed to be opened for regular cleaning will be insignificant when compared to; the loss of business, a fine from your local food hygiene inspectors, or a law suit, for supplying contaminated product. If I were you I would raise this possibility with your senior management.

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#8

Re: Pump motor still hot while the pump in right head range

04/25/2022 11:24 AM

What is the service factor of the motor?

This is a percentage of overload that the motor can endure without damage.

The service factor on many motors is 1.25,or 125%; if this is the S.F. of your motor,then it can safely tolerate up to 5 amps without damage.

How "hot" is "hot"? do you have an actual temperature measurement from the motor?

What insulation type is the motor?

A type F is rated for 105C rise,with a hot spot of +10C

A type H is rated for 125C with a hot pot of +15C

Unless your motor exceeds these temperatures and amps,there is no danger to the motor from over temp.

NOTE:Of course,you will not be able to hold your hand on the motor at these temps.

You have not given any details on the type or temperature of the oil you are pumping,and the pressure.

The viscosity of the edible oils can vary by a factor of 2,or greater, depending on temperature of the oil.

If you care to get more technical on the effects of viscosity,head,and temperature,check out this link:

https://www.jmcampbell.com/tip-of-the-month/2006/08/effect-of-viscosity-on-pump-performance/

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#9

Re: Pump motor still hot while the pump in right head range

04/25/2022 10:00 PM

You are looking at a performance curve based on (maybe) 60F water, so that curve is not indicative of your process conditions. To determine your true process conditions, you first of all need to correct your pump curve to account for both specific gravity, and especially viscosity.

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#10

Re: Pump motor still hot while the pump in right head range

04/26/2022 5:42 AM

you have great and accurate reply’s.

When pump curves are calculated, they use water , normally between 50F-70F degrees as a reference only.

you need to contact the supplier to help specify a proper sanitary pump for pumping your medium.

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#11
In reply to #8

Re: Pump motor still hot while the pump in right head range

04/26/2022 7:22 AM

The S.F and insulation type can be found on the nameplate of the motor.

A typical name(data) plate would look like this:

Manufacturer
*Rated voltage
*Full load amps
*Frequency
*Phases
*Rated full load speed
*Insulation class
*Ambient temperature
*Service factor
*Rated HP
*Locked rotor Code
*NEMA design
*Efficiency index or value
*Bearing sizes

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#12
In reply to #6

Re: Pump motor still hot while the pump in right head range

04/26/2022 10:10 PM

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#13

Re: Pump motor still hot while the pump in right head range

04/27/2022 7:17 AM

...instead of the current piece of junk.

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