CR4® - The Engineer's Place for News and Discussion®

 Previous in Forum: Capacity of Unloading Pumps Next in Forum: Help Needed on Compressed Air Vehicle
Active Contributor

Join Date: Jul 2016
Posts: 11

# Life-Cycle Cost of Submersible Pump

03/29/2017 7:41 AM

We are using Submersible Pumps whose maintenance cost is too high (i.e. their parts cost alot). So we need to get the pump from another manufacturer whose maintenance frequency and cost is lower. But before doing that I am requested to calculate the life cycle cost and efficiency of the pump in use. Now to calculate LCC, it is required to calculate energy cost, efficiency etc. To calculate them, I would require formulas for calculating these parameters. Moreover are the formula general for all types of pumps, or are they unique for submersible pumps?

Kindly provide me with the procedure and formulas for calculating efficiency and costs of submersible pumps.

Interested in this topic? By joining CR4 you can "subscribe" to

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Guru

Join Date: Apr 2010
Posts: 5914
#1

### Re: Life Cycle Cost of Submersible Pump

03/29/2017 9:27 AM

Life cycle cost for a submersible pump is pretty much the same as any other item.

"A life cycle cost analysis involves the analysis of the costs of a system or a component over its entire life span. Typical costs for a system may include:

• Acquisition costs (or design and development costs).
• Operating costs:
• Cost of failures
• Cost of repairs
• Cost for spares
• Downtime costs
• Loss of production
• Maintenance costs:
• Cost of corrective maintenance
• Cost of preventive maintenance
• Cost for predictive maintenance
• Disposal costs."

http://simple.werf.org/simple/media/LCCT/index.html

4
Guru

Join Date: Jun 2009
Location: South of Minot North Dakota
Posts: 8399
#2

### Re: Life-Cycle Cost of Submersible Pump

03/29/2017 2:36 PM

Usually when I am looking for an improved device to replace one that fails often I look at what was the common failure point of the old units design and try and find a newer version that has a better design in that weak aspect.

The most common fail points I know of in submersible pumps are the impellers and related body components wearing out due to abrasion scouring from high levels of abrasive particles in the fluids they move.

If they are plastic or composite go with stainless steel on the next units. If they were stainless steel and they keep wearing out you have a severe sediment problem with your source water you need to deal with.

Second to that is motor failure due to bad electrical control and supply issues. Either the pumps are behind cycled on and off too often or the power source has too much of a voltage drop at the motor.

Other than that without you defining the actual points of failure your pumps are having we will just be guessing at what is the source of your problem and to what can be done to fix it.

Guru

Join Date: Jan 2007
Location: Edinburgh, Bonnie Scotland
Posts: 1183
#3

### Re: Life-Cycle Cost of Submersible Pump

03/30/2017 2:18 AM

There is also the additional costs of trying to keep an older pump running past its optimum replacement time. The more often maintenance has been done, the shorter the time to the next overhaul (usually).

sometimes plastic impellers give longer life than stainless, depending on the medium being pumped.

__________________
Madness is all in the mind
Power-User

Join Date: Jan 2015
Posts: 119
#4

### Re: Life-Cycle Cost of Submersible Pump

03/30/2017 8:44 AM

Do you have other pumps? Matching brands/sizes where you can will make it easier/cheaper in the long run. Probably stating the obvious here.

Guru

Join Date: May 2016
Posts: 950
#5

### Re: Life-Cycle Cost of Submersible Pump

03/30/2017 10:19 AM

Why do we get so many, "Please tell me how to do my job." questions that apply to very basic engineering?

Guru

Join Date: Jun 2009
Location: South of Minot North Dakota
Posts: 8399
#6

### Re: Life-Cycle Cost of Submersible Pump

03/30/2017 10:48 AM

Because they weren't taught anything of applicable value in school and their now bosses and managers are mostly just bureaucrat wanna be paper shufflers that know even less practical knowledge than they do.

Power-User

Join Date: Jul 2016
Posts: 381
#7

### Re: Life-Cycle Cost of Submersible Pump

03/30/2017 12:15 PM

The formulas are similar for all similar technology pumps, i.e. centrifugal, but the life cycle cost is highly dependent on the actual equipment you are running, duty cycle, head variation, flow, temperature, specific gravity of the fluid.

You can approximate the kW demand of the pump by measuring actual motor amperes, correct for power factor, that will be simplest method to establish operating cost not otherwise apparent. Use actual motor data to establish power factor at various load points, 0%, 25%, 50%, 75%, 100%.

Other typical costs are separate seal water flows, cost per pound of treated water. Remaining costs are things you can see and count.

Power-User

Join Date: Nov 2007
Location: Bronkhorstspruit, Gauteng, South Africa
Posts: 111
#8

### Re: Life-Cycle Cost of Submersible Pump

03/31/2017 2:42 AM

From the supplier of the pump you could get the performance data sheet which will be able to tell you which pump should be more efficient.

There should be very few wear parts on a submersible pump like the impeller and seals.

Maybe you must look closer at the reason for failure and try to eliminate these. Mechanical failures are mostly related to impurities in the liquid and a strainer could help. Electrical failure is usually due to poor cooling and since the motor is cooled by the pumped liquid too high a pump head or clogging of the suction can attribute to this.

What size are the pumps? If they are small (less than 10 kw) efficiency may be of little importance, if they are big then efficiency (energy consumption) becomes important.

As mentioned in another reply the cost of downtime may be crucial.

I would suggest that you consider all these facts before you look for a formula that would provide an answer. Compile a spreadsheet with all these figures and try a 'what if' approach.

__________________
Johan van Niekerk
Power-User

Join Date: Mar 2014
Posts: 364
#9

### Re: Life-Cycle Cost of Submersible Pump

03/31/2017 3:01 PM

Not knowing much about your situation, try getting a high wear parts kit (bearings, seals, thermal overload switch, etc.) added by the manufacturer to your next pump order as part of the deal. If you have identified the major high cost wear items, but generally have reasonable service (efficiency and ease of getting into and out of the pump to do repairs, mainly) otherwise, go with the one or two brands to have given you this. If you start accumulating certain parts that are lasting longer or are finding you need parts not typically included in your purchase kit, you can get the manufacturer to adjust future kits. They will want your business.

Interested in this topic? By joining CR4 you can "subscribe" to