Pump Reliability Question

[dg47]

We are considering a pump purchase for a condition that is 1400 gpm at 550 ft TDH. The liquid is water used for cooling nozzles that spray into hot gas going to an electrostatic precipitator for gas cleaning. The operation is critical and runs 24/7. Two pumps will be installed one being an installed spare. One vendor has submitted a multistage ANSI pump and the curve looks good. The other has submitted an API horizontal centrifugal pump, single stage and the pump looks equally good. Cost of the API pump is about 3X of the multistage pumps. Loss of the pumps would be a significant operational cost. I am not familiar with the reliability of a multistage pump vs the API. Could you provided some feed back. Thanks for the help.

 

[BigInch]

I'm sure you can imagine that the 3x price tag is worth at least 3x in reliability. There is really no comparision I would care to make between the two specs based on pump curve alone. Each spec has a specific purpose. It boils down to, "Do you want chicken meatballs, or you want a thick juicy beef steak?"

Offhand lets make a rough estimate with an API reliability at 0.95 vs 0.85.
The chance of two APIs down would be 0.05^2 = 0.5% downtime.
Two nonAPIs down 0.15^2 => 97.75% reliability => 2.5% downtime. That's about 5 times less process downtime using an API. Now the question is, how much does lost production cost you?

In order to attempt to make a more or less direct cost comparsion between the two specs, you would have to consider increasing the power rating of the nonAPI you are thinking about purchasing to say 150% or more of the API pump, and also increase the maintenance time alloted to the nonAPI as well.

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"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[TenPenny]

I didn't know there was such a thing as a multistage ANSI pump.

I would lean toward the API pump if it's that critical, but also remember all of the other things you can do to improve reliability.

 

[BigInch]

I was wondering about that too, but figured the OP could sort it out if I referred to them as the API and the non-API pump, assuming that was what he really wanted to know.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[JJPellin]

We have a few multi-stage ANSI pumps. All of the ones that come to mind are vertical in-line configuration with all of the stages overhung on the end of the motor shaft. The only manufacturer's name that comes to mind is Grundfos. We use them for Chlorine eductors in our cooling towers. This is a service that we can live without for a few days with very little impact. And the pumps are so cheap, we can keep a full spare setting on the shelf in the warehouse. For a critical service that requires 24/7 operation, I would go with API.

Johnny Pellin