Help reading pump curve

[TurtleboyTom]

Motor is 50hp. Pressure gauge on discharge is reading 116psi. CAD drawing says the pump is 465 gallons @ 245 ft TDH. Does this mean the impeller should be trimmed to ~8 inches? Thanks.

 

[Artisi]

116 psi = 266ft.
Don't really understand your question:
What is the impeller diameter now?
What is the current draw at 116 psi?
What is the actual motor speed at 116 psi, not curve speed?
What is your problem - if you actually have a problem?

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.)

 

[TurtleboyTom]

The pressure is too high and I'm not sure if the impeller ever was trimmed. I'm just wondering if the impeller were trimmed to 8", based on the curve, shouldn't the head be closer to what specs call for?

 

[Artisi]

Depends of a couple of things, but in theory yes, that's assuming the impeller is oversized.

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.)

 

[TenPenny]

first question: discharge pressure is 116 psig. what is suction pressure?

 

[TurtleboyTom]

Suction pressure is about 15. There is a dp gauge across the pump and it's usually around 98 psi. I also did some more research this morning and found that the impeller was trimmed to 8".

 

[Artisi]

What is the pump speed? not the curve speed.
Can you measure the flowrate?
The pump is probably just running up the curve, it will run against the imposed head - not where you want it to operate.

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.)

 

[LittleInch]

465 gpm @ 245 ft differential head is your pump duty point. Unless TDH is supposed to mean something different to differential head....??

Your differential head, assuming you are pumping water is 225 ft. Not much of a difference but your pump curve is quite flat, hence you flow could be somewhere around 550 gpm for an 8" impellor. Just as well they put the bigger motor on it....

The pressure is too high for what? if there is no control valve on this system then the flow clearly needs the pressure you are generating, but then we nothing about your system.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[SandCounter]

I see no mention of fluid density. Normally the power demand assumes water. A different fluid will mess with both your head-to-pressure conversion and your horsepower.

I used to count sand. Now I don't count at all.