Pump expected flow from curve

[Pope33]

Hi All

I have a centrifugal pump that I am not certain what the flow is that I am getting out of it. The pump sucks from a tank 1m above it that is open to atmosphere. I have measured the shutoff head at 600kPa. The impeller size is 417mm. How do I go about doing this?

Thanks in advance.

 

[LittleInch]

You need to work out the system curve and where it intersects with the pump curve that's your flow. Follow the curve for 417mm.

Alternatively measure the discharge pressure while pumping and sees where that intersects with the pump curve. Your 1m inlet head is negligible.

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

 

[LittleInch]

Actually better to subtract from discharge pressure the height of the water level from pump inlet if it's more than 1 or 2m

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

 

[Pope33]

The pressure measurement on the discharge with the valve open was at 400 kPa. So I can assume that where the "head line" at +- 40m intersects with the 417mm impeller line, that is the expected flow beacause this is an actually point on the system curve? When looking at the curve attached it is at about 2100 m^3/hr.

 

[LittleInch]

That's about right. There is some inaccuracy in this but 2100 +/-5%.

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

 

[MFJewell]

This is what I use. I make a system curve in excel, then lay it on top of the pump curve for any pump I may use for that system.

 

[LittleInch]

If you know the system then sure, but if you only have one data point. ...

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

 

[MFJewell]

Usually a system walkdown and/or isometric drawing review will give you everything you need to make a system curve.

 

[SAK9]

I do not think you need to draw a system curve just to check how much flow you are getting out of the pump. If you know the impeller diameter you know your pump curve. Record the pump head(discharge-suction pressure) from field and use this value to draw a line from Y axis across to cut the pump curve and from the point of intersection on the curve drop a line to x axis to read off the corresponding flow rate. Looking at the curve the pump does not seem to be far off from its run-out flow.

 

[Artisi]

You also need to check power input to confirm if you are actually on curve.

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]

It's a bit close to the end of the line, but nigh on BEP. With such small difference in head it doesn't take much to make a big difference, e.g. if it was 45m instead of 40, the OP would be back to about 1750 mm3/hr.

This is a very efficient pump though - I haven't seen many with efficiency over 80% never mind 86 at the BEP.

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

 

[Artisi]

LittleInch: mid / high 80's not unusual for pumps of this size.

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]

I clearly deal with crappy vendors....

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

 

[Artisi]

Horses for courses.

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.)

 

[Pope33]

I checked the Amps on the motor today. The 250kW motor draws about 300 amps on average. Is this a bit low and what does this mean?

 

[LittleInch]

300A at what voltage? Presumably 3 phase is this amps on one phase?

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

 

[Pope33]

Sorry . 525V

 

[rotw]

This is a very efficient pump though - I haven't seen many with efficiency over 80% never mind 86 at the BEP.

And this is a pump in operation since 1992...not bad!

 

[LittleInch]

No. It's a bit high if anything for a 250kW motor. Calculated shaft power is about 265kW and 300A at 525 V worth aPF of 0.9 is 250 kW.

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