# To VFD or not to VFD: Centrifugal pump flow control

Jun 08, 2021
to VFD or not to vft that is the question that will be answered today Hello, I am Kevin Dorma, welcome back to my board, we often use

### centrifugal

#### pump

s to transfer a liquid from one place to another and we always need a way to

the

## flow

rate . We can use a valve to throttle the

## flow

or we could use a variable frequency drive or VFD to change the speed of the

#### pump

. Today we'll look at where a VFD is a good way to

### control

flow and where it's not, let's say. We want to transfer water from one pond to another and we will use a pump with a variable frequency drive for this purpose controlling the flow with the variable frequency drive requires less pumping power compared to a fixed speed pump and a control valve and this This It is because the control valve requires a pressure drop and this wastes energy, but the benefits of a variable frequency drive are only available if we can actually change the flow rate by changing the speed of the pump.
We need to observe how the pump behaves with a change in speed. and how the entire system behaves with a change in flow rate, we need an analysis of the pump and system curve, let's start by looking at how the behavior of a

### centrifugal

pump changes when we change the speed of the pump, let's look at a pump curve Typical, the pump curve is the relationship between the discharge head of the pump H and the performance or flow rate of the pump Q 100% of the pump speed there will be a certain relationship between the discharge head and the flow rate there will be a minimum flow rate below which we should not operate for prolonged periods of time and the maximum flow rate which we should not exceed at ninety percent of the maximum speed the pump curve moves as it approaches the origin the minimum flow rate is reduced Maximum flow rate also reduces and the entire curve shifts closer to the origin as we reduce speed and we can see the same pattern if we go down to 80% of maximum speed.