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No, it is not enough. In a centrifugal pump, flow rate is determined by the diameter and design of the impeller, the rotational speed and the resistance of the system. At the same speed, a higher-kW motor turns the pump at the same rate and the pump delivers the same water; the extra power simply goes unused.
Motor power is a limit, not a target
A pump operates at the point where its curve meets the system curve, and draws the shaft power required at that point. The motor's kW rating must be large enough to meet this demand; a larger rating does not change the operating point. If the existing motor is already sufficient, upsizing it only changes the cost and, often, the frame size.
Why is raising the speed risky?
Driving a pump designed for 1450 rpm with a 2900 rpm motor roughly doubles the flow, quadruples the head and increases the power eightfold. In most pumps this leads to the following problems:
- Exceeding the pressure limit of the pump casing and seals
- Cavitation on the suction side; pitting and vibration on the impeller surface
- Exceeding the design speed of the mechanical seal and bearings
- The need to resize the motor and the cable
This route should not be tried unless the pump manufacturer permits a higher speed.
Realistic ways to increase flow
- If the pump catalogue lists a larger impeller diameter for the same casing, check the motor against the power for that diameter
- Reducing system resistance: undersized pipes, dirty strainers, throttled valves and unnecessary elbows
- Choosing a new pump suited to the requirement, or connecting a second pump in parallel
In every case, the target flow and head must be defined first, and the motor power derived from this new operating point.
The relationship between operating point and motor in volute-casing pumps is explained on the centrifugal pump motors page. Once the power for the new operating point is known, you can compare suitable models using the criteria under pump motors.