6 replies to this topic

[PENGG]

Few centrifugal pump have minimum recirculation flow provision few dont have.
1. What is the criteria to provide or to not provide minimum recirculation flow line in centrfugal pump ?
2. What should be the size estimation for new pumps ?
3. Why to add minimum recirculation flow to rated flow of pump while doing hydraulics ?
4. Why to consider only one flow (Normal flow i.e. minimum recirculation flow) in minimumrecirculation valve sizing ?

[breizh]

Hi ,
Consider this resource . This topic has been discussed many times in this forum and you should use the search function (top right) prior to post .

Hope this helps you

Breizh

[PENGG]

Mr. Breizh,
Thanks but its not the complete answer of my question.

[breizh]

http://www.pumpfunda...circulation.pdf

An other good one !
Breizh

[fallah]

PENGG,

1-Having continuous operation and having a power so high can generate a lot of heat due to shut off
2-Not clear question
3-It is to be included in rated flow when minimum recirculation flow will add to the suction flow
4-In minimum flow control valve sizing the minimum flow will normally be considered at least equal to 5% of the required pump's minimum flow

Edited by fallah, 28 December 2012 - 10:52 AM.

[S.AHMAD]

1. What is the criteria to provide or to not provide minimum recirculation flow line in centrifugal pump ?
Two reasons that I am aware of: one is the possibility of temperature rise leads to cavitation and or pump casing explosion. If temperature rise is too small or insignificant, then minimum flow due to thermal is not required. Secondly, possibility of fluid recirculation leads to cavitation and excessive vibration. Thi is normally so for high head and high capacity pump. The minimum recirculation rate is normally stated by the pump vendor.

2. What should be the size estimation for new pumps ?
The problem normally arises at the design stage where pump is not yet available and hence minimum continuous stable flow is unknown. Experienced engineers will tend to use their experience to bridge the gaps. Unfortunately, there is no specific rule of thumb. My suggestion is design the recirculation rate for 50% or 70%.

3. Why to add minimum recirculation flow to rated flow of pump while doing hydraulics ?
Whether need to add or not depends on the type of recirculation mechanism. For continuous recirculation using orifice plate, yes you need to add. If using control valve no need,

4. Why to consider only one flow (Normal flow i.e. minimum recirculation flow) in minimum recirculation valve sizing ?
One is enough! No reason to have more than one flow for sizing.

Edited by S.AHMAD, 31 December 2012 - 02:30 AM.

[PENGG]

Dear Mr. s Ahmad,

Excellent answer and superb way of answerng it.

Edited by PENGG, 31 December 2012 - 08:10 AM.