Dear,
I am working in selecting a flow control valve located downstream of positive displacement pump.
specs is requiring that CV to be between 30% for minimum flow, 50% for operating flow and 70& for maximum flow,
looking at the pump curve (flow and head) it turns out to be a linear curve. so the valve manufacturer considered in his CV calculation that the normal pressure to be 10bar which is the operator pressure, min and maxi pressure corresponding to max and min flow to be 4bar and 16bar.
first question that crossed my mind, how do we decide on the maximum and min pressure? please see pump curve attached, is there any rule for it.
second, he selected a control valve with linear type, which is logical corresponding to the fact that it is located upstream of a positive displacement pump that has linear characteristic.
and the results that he got for the selected control valve
for the normal flow it is around 50% of valve opening which is as required
for maximum flow (which corresponds to min pressure of 4bar), he go 52.6% of valve opening (required should be 70%)
for min flow (which corresponds to max pressure of 16bar), he got 43% of valve opening (required is 30%)
so I am little confused how we do we usually select min and max pressure for them to select the FCV since they affect the CV.
second I find that the valve has problem in rangeability which I guess might have problem when we control it.
Please refer to attached P&ID, were the FCV in concern is FCV-7041 located in the middle of clouds in FCV1 attachment, FCV0 attachment shows location of the positive displacement pumps upstream of the FCV-7041.
any feedback are really appreciated,
thanks a lot!
Charbel
I am working in selecting a flow control valve located downstream of positive displacement pump.
specs is requiring that CV to be between 30% for minimum flow, 50% for operating flow and 70& for maximum flow,
looking at the pump curve (flow and head) it turns out to be a linear curve. so the valve manufacturer considered in his CV calculation that the normal pressure to be 10bar which is the operator pressure, min and maxi pressure corresponding to max and min flow to be 4bar and 16bar.
first question that crossed my mind, how do we decide on the maximum and min pressure? please see pump curve attached, is there any rule for it.
second, he selected a control valve with linear type, which is logical corresponding to the fact that it is located upstream of a positive displacement pump that has linear characteristic.
and the results that he got for the selected control valve
for the normal flow it is around 50% of valve opening which is as required
for maximum flow (which corresponds to min pressure of 4bar), he go 52.6% of valve opening (required should be 70%)
for min flow (which corresponds to max pressure of 16bar), he got 43% of valve opening (required is 30%)
so I am little confused how we do we usually select min and max pressure for them to select the FCV since they affect the CV.
second I find that the valve has problem in rangeability which I guess might have problem when we control it.
Please refer to attached P&ID, were the FCV in concern is FCV-7041 located in the middle of clouds in FCV1 attachment, FCV0 attachment shows location of the positive displacement pumps upstream of the FCV-7041.
any feedback are really appreciated,
thanks a lot!
Charbel