Pump selection
Pump selection
(OP)
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?
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?





RE: Pump selection
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
RE: Pump selection
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.
RE: Pump selection
RE: Pump selection
KSB = 22 HP
Flygt = 35 HP
RE: Pump selection
RE: Pump selection
Grundfos gives something similar to KSB (21 HP).
Might be Flygt.
RE: Pump selection
RE: Pump selection
RE: Pump selection
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.
RE: Pump selection
RE: Pump 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.)
RE: Pump selection
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.
RE: Pump selection
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
RE: Pump selection
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.)
RE: Pump selection
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.
RE: Pump 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.)
RE: Pump selection
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.
RE: Pump selection
They just gave me a fairly good price quote for this project though (with a 12 weeks delay for transport).
RE: Pump 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.)
RE: Pump selection