Shutoff pressure 2

[Vishal Kumar]

I have a query , we have a reactor pump system (working+standby) same suction line obviously.
Shutoff pressure for both we are getting different. How is this possible?
Impeller we have checked for both & are matching to the specification and with each other.
Is RPM a possibility, that one of the pumps are running at a different RPM?

 

[LittleInch]

Yes.

Or one is going backwards?

How different? 5% is not unusual.

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

 

[TiCl4]

Even if both pumps are specc'ed identically, they may differ in flow and shutoff head. See link below for tolerances at different certification levels:

https://www.wilfley.com/high-performance-in-centrifugal-pump-testing-standards/

 

[mk3223]

just curious and it could be very helpful to verify the pump/motor tags and or pump performance curve doc to clarify the question.

 

[Vishal Kumar]

Discharge pressure for one pump is 3.9 kg/cm2g
Other one is 2.2 kg/cm2g.

 

[Vishal Kumar]

Verified the curve , the curve developed is same for both the pump tags & what I mentioned above is the shut off pressure seen from discharge PG & PT also.

 

[FMJalink]

With such differences in shutoff pressures, your suspicion on rotational speed differences seems correct. Roughly the ratio of the head developed is equal to the ratio of the rotational speed to the power of two. Maybe the nominal rotational speed of the electric motor can (still) be read from the electric motor tag. Other method would be, if you can determine the suction pressure, check whether the ratio in pressure increases is approximately 4. Would mean that one electric motor has 2 poles and the other 4 poles.

 

[LittleInch]

Find and post the data sheets and test data for the two pumps and also a photo of the motor plates.

Check rotation is correct.

Check no constriction in the pump or pipework or valves. Do you use the same guage or transmitter?

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

 

[pierreick]

Hi,
What is the shut off value (Qv=0) from Pump curve (manufacturer)?
BTW the way you may want to share with us the pump curves and the specification sheets associated with those pumps.
You should have checked the RPM before asking the forum, this is ridiculous!

Pierre

 

[Vishal Kumar]

What seems ridiculous in asking mate ? It's a technical question from my end ? Our maintenance team is very occupied & it's a ground reality that I want to eliminate the easy options instead of making maintenance team work. It's just how I work. Also
New update : we don't have tacho meter , we are trying to bring a service person

Both pump discharge pressure are measured from both pump discharge pg (2nos) and a common discharge header PT.

 

[Vishal Kumar]

I will send the curves today , please wait.

 

[mk3223]

It seems that two original pumps are the same size based on the tags and performance curve.
I suspected that the different reading of the pump discharge pressures as seen on PG and PT may be caused by the reasons, such as pump damage, impeller corrosion, etc.
- how long the pumps in service?
- what's the pump inspection record?
- any maintenance history or record?

 

[Vishal Kumar]

Both pumps are identical, they even have a common pump curve with both tags A/B.
Pumps were procured but over a year since they were not started. We are conducting water trials now.

 

[LittleInch]

Is the motor three phase?

If so it might be going the wrong way round.

Have you checked rotation?

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

 

[Vishal Kumar]

Yes rotation is correct. Checked.
Impeller checked found OK.
160 & 158.5 mm. Not enough to make that much difference in shut-off checked from affinity law.
RPM sensor hasn't arrived yet but it is without VFD so I don't think it will affect , being a DOL starter.

 

[Vishal Kumar]

Yes 3 phase motor

 

[LittleInch]

OK,

Next is to see what the motor plate says just incase they've swapped motors for some reason.

How are you testing shutoff (no flow) pressure? Is that shutoff valve leaking? Is there a relief valve somewhere relieving the pressure on one pump and not the other?

Can you post the P&ID of this set up?

something is different between the pumps - only you can see what it looks like on the ground or how ops are testing it.

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

 

[pierreick]

Hi,
So far, no pumps curves, no ID/PFD, no information about the name plates, no data sheet from vendor!
By the way what is the objective of the investigation, training? What is the real problem?
Pierre

 

[pierreick]

Hi,
A good resource to support your work.
Good luck
Pierre

 

[Vishal Kumar]

I will share all details today , apologies for the delay , it was a company document hence making caution before sending & keeping only process detail .
But I have checked all and found OK.
And this is a real life issue I'm getting, pump trial if successful I will proceed for the flow trial by opening discharge which goes into a catalyst filter. Please wait for my documents.