3 replies to this topic

[abo annas]

Hi,all
in our oil and gas station we have 2 centrifuge oil pumps are runing in parallel,but due to the slugish of disharge LCV,during low level on the LP oil vesel,the LCV is not responding quickly to close,and if it,s responding and close another problem is created due to minimum recycle flow is not opening quickly to compesate the level on the vesel,and to prevent the low discharge flow from the pump,so my quistion is ,many times we are controlling the recycle valve manually,i.e since we face low level on the lp oil vesel jusy immediatlly we put the recycle LIC on manual and open to 100%,is there any harm for the pumps from this operation?
any more info, iam ready.
Regards.

[kkala]

I understand that you open the recirculation min flow valve manually (intervening on its controller) at low level, waiting for the LCV to close. There is no harm done on the pumps in this way, since flow rate is maintained higher or equal to minimum flow.
Of course min flow valve should not open too abruptly to avoid hammering (indicated by some noise).
However the system has the risk of letting the pump cavitate in case of human error, e.g. when approaching low level is not detected in time. So replacing the controllers with fast responding ones (or adjusting the existing ones) had better be tried.

Edited by kkala, 15 June 2010 - 03:31 PM.

[fallah]

The function of minimum recycle flow in centrifugal pumps isn't compensation of the level in an upstream vessel.

The set point of the LCV should be a value between HL and LL; thus, in normal condition the LCV opens to maintain a normal level.

It seems that the LCV in your system should be changed to a FCV cascaded with a LT on the vessel.

For pump protection against a low level, normally a dedicated LT on the vessel provides LL alarm that has an interlock activates a pump shut down.

[demank]

I think you should reset your LCV. Or consider to change it, because of its malfunction.