PCV and FCV set points and work princilbe valve on cetrifugal pumps ?
PCV and FCV set points and work princilbe valve on cetrifugal pumps ?
(OP)
PCV, FCV are added to centrifugal pumps for minimum flow incase of blockage in discharge side
The question is how PCV, FCV set points are determined and calculated on centrifugal pumps with fixed RPM and variable RPM
The question is how PCV, FCV set points are determined and calculated on centrifugal pumps with fixed RPM and variable RPM





RE: PCV and FCV set points and work princilbe valve on cetrifugal pumps ?
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RE: PCV and FCV set points and work princilbe valve on cetrifugal pumps ?
Setting up a PIC in min flow service in a fixed speed application would only be possible when both of the following are true:
a) Suction pressure at the source vessel is more or less constant
b) Fluid density is relatively constant.
Else an FIC would be the way to go. Pls note that where (b) is not the case, a diff pressure based FE (orifice plate, venturi etc) is not a good choice either when density compensation is not done for the FIC loop. In such cases, use other FEs' such as vortex meters, ultrasonic etc.
RE: PCV and FCV set points and work princilbe valve on cetrifugal pumps ?
1. Fixed are Restriction Orifice (RO)
2. Direct Acting Pressure Control Loop
2. Reverse Acting Flow Control Loop
1. Fixed Area RO
This is suitable for centrifugal pumps with relatively low flow and low discharge pressure, because high differential across the RO would lead to choked flow through the RO bore, and constant flow through the RO means continuous energy loss.
2. Direct Acting Pressure Control Loop
As the delivery through the pump decreases, pressure increases. Rate of increase of discharge pressure depends on the H-Q curve of the pump, provided by the vendor. Increasing pressure, thus means that the pump is shifting towards its shutoff. looking at the pump curve, minimum flow point with corresponding differential head may be determined. With appropriate safety margins, a setpoint can be given to the pressure controller to open the kickback valve when the pressure approaches towards the setpoint.
This method is suitable for the pumps with steep H-Q curves where drop/rise in pressure is more prominent in a given window of flow change
3. Reverse Acting Flow Control
In this control philosophy, in a situation of zero forward flow, control valve remains open to ensure delivery of minimum flow through the pump. As the flow is taken by the consumer, total flow at the discharge of the pump starts increasing. In response, the control valve start closing so that total flow (forward and recycle) remains equal of above the minimum flow setpoint. The kickback valve closes fully, eventually when forward flow exceeds the setpoint
This scheme is suitable for the pumps with curves where incremental rise in discharge pressure is not significant compared to the magnitude of the flow reduction
RE: PCV and FCV set points and work princilbe valve on cetrifugal pumps ?
(c) the Q-h curve at around the location of the min flow should show a fair change in h for a small change in Q. A flat curve, or a near flat curve at around this location indicates the non viability of a min flow PIC.