17 replies to this topic

[arun261085]

Dear All,

Iam having one basic quiery on centrifugal pump operation. If the suction pressure of the centrifugal pump increases due to increase in system pressure on suction side. What will be the impact on discharge pressure of that Pump???

Regards
Arun Kumar D

[Raju Gawande]

With increase in suction pressure discharge pressure of pump will increase.

[Rahimzadeh]

Dear arun:
With increasing suction pressure the pump TDH (total differential head) will decrease and pump operating point will shift to right (higher flow).
i must say the suction pressure increase is not mean that same amount pressure increase in discharge of pump .
in addition the discharge pressure, the pump flow rate is increase as performance curve.

[S.AHMAD]

Dear Arun
1. Please consider these three cases:
Case 1: If the system has a flow control valve at discharge, the discharge pressure will increase proportional to the increment of suction pressure. If, for example the current discharge is 1000 kPag, if the suction increases by 200 kpa then the discharge will be 1200 kPag. Flow rate remained the same.
Case 2: If the discharge has a pressure control valve that is controlling the pump discharge pressure, any increment on the suction pressure the pump discharge pressure remained the same but flowrate will increase.
Case3: If no control valve, the discharge pressure increases according to the pump characteristic and system characteristic. The pressure and flowrate are the meeting point of the two characteristics curve.
2. The above cases are for centrifugal pump ONLY but not for positive displacement.

Edited by S.AHMAD, 31 March 2012 - 09:57 PM.

[S.AHMAD]

Additional comments to Case 3 in post#5.
This is due to the fact that pump performance characteristic does no change with suction pressure but the system characteristics shifted to the right with increasing pump suction pressure. The y-axis intersection point of the system characteristic is lower by the same head value correspond to the pressure increment.

Edited by S.AHMAD, 31 March 2012 - 10:05 PM.

[sheiko]

Another resource that answers the question asked:
http://www.chemicalp...s/2007/002.html

Edited by sheiko, 31 March 2012 - 10:54 PM.

[S.AHMAD]

Dear Bro Sheiko

If however, the discharge pressure of the system rises as a result of the suction pressure increase, then the system curve will stay the same and, as the pump curve will also stay the same, there will be no change in capacity.

The above is an extract from the link. I do not agree with the statement that the system does not change with change in source pressure (lead to higher suction pressure). You will find the correct answer by deriving the system curve at two source pressure. Unless if someone does know how to do that!

The pump characteristic curve does not change with source pressure/suction pressure - AGREE 100%. System curve does change,

[Mayank Joshi]

what about the power consumption of the pump.?
will increasing the suction pressure of the pump reduce its power consumption ?Flow remaining the same ?

[breizh]

http://centrifugal-p.../sitemap_2.html

 

http://www.webbpump....cal-sealing.php

 

Consider this resource to support your query.

Breizh

Edited by breizh, 14 February 2013 - 02:04 AM.

[Mayank Joshi]

this is a very nice link , but can you please tell me if the flow is constant will increasing the suction pressure of a centrifugal pump reduce the power consumption?

[thorium90]

Hi,

This nifty website appears to answer your question

http://rpaulsingh.co...lems/Ex2_13.htm

[Mayank Joshi]

thanks a lot !!!
this site shows that if for a pump SP is increased keeping the DP and flow constant the power consumption decreases. 

Can anyone explain this?

[meetyourmaker]

Dear mayank,

a centrifugal pump produces a fixed head at a particular flow rate. so if by some means Differential Pressure is fixed the flow rate gets fixed and so does the power consumption for a fluid of knownSG. So power consumption will remain the same if Diff Pressure is same when suction pressure is increased

Edited by meetyourmaker, 13 February 2013 - 10:33 PM.

[Mayank Joshi]

actually the power consumption of a pump is Head produced * flowrate
on increasing the SP the head to be produced decreases (keeping the DP constant) and as the flow rate is the same therefore power consumption decreases.

i wanted to know that if we have a flow controller at the discharge of a pump and before increasing the suction pressure I keep it on Manual ie I am fixing the system resistance so DP will remain same and i think flow should increase, and since I want the same flow as before i will manually Pinch th control vavle , now as valve is closed the system resistance increases and therefore Pump DP will increase. How can I maintain same DP and flow by increasing SP??

[meetyourmaker]

no mayank on increasing SP if for a certain pump system if Differential Pressure is same then head developed by pump(Diff Pressure/density*g) is same so power is same. IF by DP you mean discharge pressure then if DP is kept constant when increasing SP then power increases and flow increases and head decreases, there is no way of  keeping both discharge pressure and flow constant in this case, i has to be according to the pump curve

in a flow cntrol setup if suction pressure is increased , the flow rate through the system increased innitially, the flow control valve starts to close and and when equilibrium conditions are again established , the control valve will have more pressure drop across it to maintain the same flow. the static head loss term in the system curve will reduce and the frictional head loss term will increase.So the same differential pressure is maintained across the pump and same flow goes through the system its just that the control valve has to cause more pressure drop.

Edited by meetyourmaker, 13 February 2013 - 10:38 PM.

[Mayank Joshi]

By DP i meant discharge pressure.

so does this mean that if my flow requirement is fixed than any increase in my SP will propotionally increase my DP and power consumption will remain the same or in other words I cannot fix both my flowrate and DP while increasing my SP

[meetyourmaker]

mayank 

you are correct.

[Mayank Joshi]

thanks