How long centrifugal pump can work on minimum flow for commissioning purpose? 5

[Nick4684]

Normally we are doing 4hrs MRT (mechanical run test) for commissioning of pumps.
Now I have pump, 400Kw- 350m3/hr, (min. flow 100m3/hr)- 50bar discharge pressure and 260m head
any idea for how long can I run it for MRT on minimum flow line to check pump overall performance, vibration, temperature?

 

[Artisi]

I see absolutely nothing of value in running at low flow for more than a few minutes other than to check for leaks in the system, that can better be accomplished using better methods anyway, as for vibration, alignment, power input, flow / head, suction conditions etc. completely useless as nothing is achieved, The time to check is when the system is completed, the pump can then be run to establish the flow /head/power input vibration etc at its real operating point that will more than likely not at the fictious design point anyway, together with partial flow conditions if considered necessary.

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.)

 

[1503-44]

Agree. All that should be done before the system is ready to go full, is a "bump test".

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[Nick4684]

Thank you all guys for provided responses, flow will be controlled by FCV (flow control valve).
It is not bump test- I am going to do Mechanical Run Test to see pump performance, vibration, temperature, Current etc.
when pump working on min flow (100 m3/hr) discharge of pump would be 100m3/hr regardless of having constant speed motor.

 

[1503-44]

Where is that 100m3h going? Direct to recycle?

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[Nick4684]

yup, 100 m3/hr go directly to suction header 16" pipe.

 

[1503-44]

With no other outflo, right?

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[Artisi]

Please explain, all the supposed testing and data will be collected at a restricted minimum flow, am I correct in assuming this?

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.)

 

[Nick4684]

@1503-44: correct, just on recycle mode
@Artisi: correct, all the supposed testing and data will be collected at a restricted minimum flow

 

[1503-44]

Please let me know how long it takes to hit 250F.

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[Artisi]

Lots of luck, would be greatly interested in what was achieved at restricted flow - other than nothing useful, as for the pumps operation at its designed duty - guess that's irrelevant.

Would have thought by now a few bells might be ringing, but then, what would the collective knowledge here really know?

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.)

 

[Nick4684]

Thank you guys for all of your valuable inputs,
I double checked with vendor as well,
there is possibility of temperature increase if pumps run for long time on the min flow, as you already mentioned;
So it seems, there is no point for running pump for more than 30' just to have a general check everything working Ok, there is no leakage or abnormal noise / vibration.

 

[1503-44]

Cut that time in half and keep your eye on the thermometer.

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[LittleInch]

So I used 50m of 12"pipe as your closed circuit system.

At min flow I get a temp rise of 1C every 2 minutes. So 30 mins is 15C. Should be OK.

Longer or bigger diam pipe more time/ less temp rise shorter smaller diam less time / greater increase. .

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[1503-44]

Isnt 50m a bit long? I used 20m of 4".

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[LittleInch]

At a design flow of 400 m3/hr is going to be bigger than 4". This is the complete circuit remember.

Might only be 20m, no idea.

That was just to get some idea of what the heat up time was, seconds, minutes or hours.

Looks like minutes.

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[1503-44]

The main, yes, that would be 10-12-14", but this recycle line may be only a short, small diameter line with maybe a a control valve(?) going immediately from discharge to suction. But I admit I don't know. Only basing that on the Site 1 pump configuration I found in my files.

But true, to do 30m, some volume of cooler water has to be contained in a long loop back, or somewhere.

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[Nutzman]

Typically in centrifugal pump curves, the start (point) of the NPSH curve is the minimum flow for the pump.
In answer to a point made above regarding pump performance test "the test is to prove the pumps performance at a given duty point. Namely Head, flow and power absorbed at duty point (efficiency)" In terms of "BS EN ISO 9006 2000 (Rotodynamic pumps – Hydraulic performance acceptance test – Grades 1 and 2)" a single duty point is agreed upon between the client and the supplier/test bed. Not 20%, 40%, 60%........?