35 replies to this topic

[pallavikhatri]

Dear All
When we add the minimum circulation flow to the normal flowrate of the pump when a restriction orifice is present in min. flow bypass line, then do we have to consider the head from the pump performance curves corresponding to the normal flowrate plus the min. bypass flowrate. Will the head change in that scenario?

Pallavi

[fallah]

pallavikhatri,

The minimum recirculation flow of the pump should already be included in the pump's normal flow passing the pump, hence the corresponding pump's head would be obtained from the relevant curve. Obviously, the process normal flow would be pump's normal flow minus minimum recirculation flow passing the RO.

Fallah

[pallavikhatri]

Thanks Fallah for the reply

[pallavikhatri]

Hello everyone
Can anyone tell me what is the purpose of providing a globe valve upstream of the restriction orifice in the minimum circulation flow when the purpose of the both the globe valve and restriction orifice is the same.

Thanks in advance

Regards
Pallavi

[fallah]

Pallavi,

Normally in a pump with an almost fixed working point no need to such globe valve, but considering lack of information about the pump operation it just could be said that: 1) probably mentioned pump is working within a range of flowrates and its minimum flowrate needs to be adjusted by a manual globe valve due to changing the operating condition across the RO, 2) the RO is oversized and the minimum flowrate needs to be adjusted .

Fallah

Edited by fallah, 07 April 2012 - 02:41 AM.

[Bodhisatya]

This indeed is a very good discussion going on.I will like to ask the honourable members something.Currently I am working in an Air Separation Unit ,where we have a five stage Centrifugal Pump with Water as a working Fluid.the Water goes into a Vessel which has an air Pressure of 8.7 Bar(g),the Pump discharge is something around 9.8 Bar(g).The Problem is that the pump is giving the required head but not the required flow is supposed to be 10 m3/hr,as against the current value of 6 m3/hr.

On confronting the Vendor they said that we are operating the Pump at a higher discharge Pressure than the rated ,which is resulting in low flow.Is this the possible reason.If yes then please suggest me a way out how to eliminate this problem.

Thanks and Regards
Bodhisatya.

[pallavikhatri]

Thanks Fallah for the reply.
But the minimum circulation flowrate for a pump is fixed and thus the flowrate through a RO is fixed, so for the constant flowrate do we have to provide a globe valve upstream of the RO.

Thanks
Pallavi

[fallah]

pallavi,

Generally for constant minimum flowrate you don't need to have a globe valve in upstream of the RO. But as i mentioned, if the pump is working within a range of flowrates due to, let say for instance, having two speeds characteristics the minimum flowrate cannot be fixed and might need to be adjusted manually by e.g. a globe valve.
It is just my guess and if you want to have a better input you have to submit the detail information about the pumping system.

Fallah

[S.AHMAD]

Bodhisatya
1. The problem with the hydraulic system that you have is that the pump does not match with the system performance curve.
2. This is probably the vendor did not supply the right pump as per your specification or you gave incorrect information to the vendor or there is misunderstanding between you and the vendor.
3. Contractually, the vendor should be responsible to supply you with the correct pump as being specified, therefore it is their responsibility to make corrective action. If the failure is on your side for not giving the right specification, then the vendor can wash their hand.
4. The most common way to resolve this type of problem is to change the pump impeller size, if it is not yet the maximum impeller size.
5. Second option is to increase the line size. However, if the pressure requirement is mostly due to elevation, this option is useless.

Edited by S.AHMAD, 09 April 2012 - 02:58 AM.

[shin29]

Hi,

i want to know about centrifugal pump minimum bypass flow, can you please send me the files to study which were mentioned in the discussions above

1) published in "Hydrocarbon Processing", July 1995.
2) I.Taylor "Pump Bypasses now more important", Chemical Engineering, May 11, 1987, pg. 53.

Thanks
sahil

[atulsavant]

Can u forward above documents on

 

 

Regards,

Atul