pump graphs... here is a silly question!

[Seanbreen]

hello, ive just started a new job 2 weeks ago and have been given a small project but where is the question...

if the pump is rated to 410m3/s at 35m @ 1750rpm

and ive got the pump curve

why whould this nember not be shown in the chart? this point is about 10% too low on the graph, if 410m3/s is fed in to the graph i get 40m

cheers
Sean

 

[CanuckMiner]

I do not understand what you mean by "the pump is rated to...". Is that supposed to be the Best Efficiency Point for the pump? Or is that the duty that someone else gave you (i.e. someone is asking for a pump that will deliver 410 m3/s at 35m head)? By the way, I think you mean 410 m3/hr, not per second, unless you have a power supply that will yield about 200MW. ;-)

Regardless, you should develop a system curve and plot it against the pump curve. Where the two intersect will be your operating point.

Cheers,
CanuckMiner

 

[rzrbk]

Usually the rated head and capacity are shown on the pump curve with a bold arrow drawn onto it. I am used to seeing the rated point a little bit lower than the curve, but not to the extent above.

Things to check:
-Impeller diameter same as shown on curve?
-Was a performance test done on this pump? If so, you
should have a specific curve for the pump instead of a
generic one. (will have serial number, impeller trim,
date, etc. shown on chart)
-If pump is installed, the dead head pressure (pressure developed with no flow) can usually be checked to confirm whether it is operating on or below the curve.

 

[electricpete]

I'm no pump guy but a few more thoughts to throw in:
1 - Is the speed on the curve shown as 1750?
2 - The mention above that rated is usually less the curve makes me wonder if the manufacturer might build in a little margin. The curve might be like a best estimate new and the rated sort of like a minimum value? I don't know but just wondering aloud.

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[electricpete]

Another thing to check would be number of stages identified on the curve vs actual number in your pump.

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[JJPellin]

There is one other thing that I come across regularly. In order to be able to make their mass balance work out, our process engineers measure all flows in standard volumes. That is to say, what would the volume of the liquid be at 60 °F. For a very hot stream, it can change the flow rate by 20%, 30% or even more. Make sure you know what units they are using to measure the flow. If they are using standard units, you will need to know the ratio of hot (actual) and cold (standard) specific gravities for the fluid. For hydrocarbons, there are good generic charts available that show the SG ratio based on temperature change.

 

[rmw]

Is your pump actually operating at 1750 RPM? Or is it operating on 50Hz power?

rmw

 

[abeltio]

this means that the pump will be able to supply the duty requested, with some extra margin.
on the contrary, if the pump @ 410 m3/h developed only 30m then it is too small for the service.

what happens is that the diameter of the impeller must be machined to give exactly the head you need or...

draw the curve of the system and see what is the actual operation point.

saludos.
a.

 

[Seanbreen]

Yeah good points!
going to have a proper look at it on monday!

I'm not very experianced with pumps and the accociated diagrams. Yeah its shown as 1800RPM in the curve but i made an allowance for this.

pump specs(off the top of my head):
1750 Rpm,
75KW,
77% hydraulic efficiency,
114 L/S,
3 phase,
460V,
1900kg dry with skid,

it is used for hanging off the side of an oil rig to supply another booster pump on the deck... check some of the pics out thay are quite cool!

http://www.rigcooling.com

thats about all i can remember at the moment... had a bit of a heavy night yesterday so not feeling my best!

 

[stanier]

Suggest you go to

http://www.mcnallyinstitute.com

and learn a few things aboout pumps and pump curves.

 

[MortenA]

some questions pops into my mind

1) Are you pumping anything else but (sweet) water at 60 deg F?

2) Are the impellars the same as for the curve

3) Since you speed is slower than the design speed you would expect a lower head - but you find a higher. Have you gotten it backwards in you compensating? (or am i misunderstanding you)?

Best regards

Morten

 

[Seanbreen]

hello,

Yeah ive read most of that site, its just this bloody curves are not correct!

as for the Questions:

No,

Yes,

Yes ive assumes a slightly lower head, its still about out 10% out...

going to call the makers and have a convo with the person there! There might be a good reason for it!

 

[Artisi]

Does the curve you are referring to actually belong to the installed unit or is it a generic curve that has been supplied. It's always best to ask the right questions, usually of the pump supplier rather than second guessing.

Naresuan University
Phitsanulok
Thailand

 

[Seanbreen]

The curve apparently belongs to the pump and motor supplied... i have not been able to get hold of the guy that "is the one to ask" at the company. and i doubt i'll have time today to do it.

it will be interesting to see how he has calculated the supplied results... i'll keep you informed.