Pump selection 1

[SMIAH]

I need to choose between 2 pumps for wastewater pumping :

1) KSB : KRT K 80-251/172UG-S
2) Flygt : N 3171HT-4''

Both seems to be efficient for 380 USGPM at 111'.

I is 29 HP and the other 18 HP.

What should I check?

 

[LittleInch]

The pump curves (can you upload both).

Are you quoting shaft (pump) power or size of motor being offered? At 75% eff I get about 14hp shaft power for your figures. Maybe the other vendor just doesn't have motor the right size?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[SMIAH]

Motor rated power.

Flygt:
• Rated power : 26.1 kW
• Speed : 3530 rpm

KSB :
• Rated power : 13.1 kW
• Speed : 2915 rpm

Pump curves attached. Might look for other vendors.

 

[SMIAH]

KSB'one

 

[SMIAH]

Sorry confusion about motor rated power:
KSB = 22 HP
Flygt = 35 HP

 

[DubMac]

Without having looked into the details, the speeds you mention make it seem that you are comparing a 50cycle against a 60cyle motor.

 

[SMIAH]

Think you got it.

Grundfos gives something similar to KSB (21 HP).

Might be Flygt.

 

[SMIAH]

Human error always end up as the prime suspect for invalid data.

 

[DubMac]

And if you torture data long enough, you can make it confess to anything.

 

[SMIAH]

Checking a little more (60 hz) :

Flygt
57.5%/3600 RPM/17.2 kW
GrundFos
59.9%/1746 RPM/15.8 kW
KSB
66.9%/1752 RPM/17.1 kW

Price now.

 

[SMIAH]

Let's start another thread about motor speed now (3600 vs 1800 RPM).

 

[Artisi]

No need, see if Flygt have a 1780 rpm selection.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[BigInch]

You should also check what power rating you need.
Check the maintenance and reliability requirements too.
Generally 3600 rpm machines are smaller, cost less, but usually don't last so long, or require more maintenance.

Independent events are seldomly independent.

 

[LittleInch]

I'm not sure if you're looking at motor rated power or pump absorbed power. The motor rating only affects the start current and not the normal operating current.

For the same duty and the same liquid, a lower efficiency pump will use more power in operation, hence your figures for Grundfos and KSB above look like motor rating - a lower efficiency pump cannot use less power than a higher efficiency pump.

Pumps only consume the power they need to do the duty they experience. You could put a 30kW rated motor on any of these pumps and they would still use the same amount of power, just that you paid more for your motor.

If you think you're ever going to operate to the right of your duty point, then get a bigger rated motor becasue it will be able for the extra load, but if you're confident that your system will remian the same, then get the highest efficiency pump regardless of motor rating.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Artisi]

Just to expand on what LittleInch has raised is the way motor power is usually reported for submersible pump compared to non-submersible pumps.
Non-sub pumps report power at the input shaft there as for submersible units the power is usually reported as power at the motor terminal. So when comparing submersible against non-submersible you must ensure you are comparing total power input of both, likewise if comparing hydraulic efficiency.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[SMIAH]

Thanks guys. It was motor rated power.

Flygt do have a 1800 RPM motor too. I'll let them specify something now.

I didn't know Grundfos had submersible pumps for wastewater.
I'll check ABS, KSB, Flygt, Fairbanks-Morse and Grundfos.
Might be a little small for some of them though.

 

[Artisi]

You can't go past Flygt,ABS and KSB, Grundfos make excellent pumps but I think the first 3 in the order listed are your best options.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LaBamba]

Consider also the differences in impellers. The Flygt N-Series is a different style (cleans itself on every rotation) from the KSB, the Grundfos. It might be better for you (if you have stringy solids present) or it might not; the cost difference may not be justified. Also remember that the N-series efficiency remains constant as any non-self cleaning impeller's efficiency drops as solids build up.

Another consideration (and I've run into this) is, where is the pump coming from? Flygt pumps are made in Europe or the US. KSB is, I believe, made in South America. While I've never experienced any problems importing European equipment, I have with gear from South America (please correct me if I'm wrong about that). For some reason, customs is suspicious of imports from that region (hmm). If you ever find yourself in need of a quick replacement, that factor can be important.

 

[SMIAH]

It takes longer to get KSB parts/pumps in here. Maybe it has to do that it comes from South America as you pointed out.
They just gave me a fairly good price quote for this project though (with a 12 weeks delay for transport).

 

[Artisi]

LaBamba: what makes you believe that KSB (a German pump company) are manufactured in South America.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)