HomeExperienceDifferences between VFD and fluid coupling in controlling pumps

Differences between VFD and fluid coupling in controlling pumps

Regulating the speed of the pump by using of either a variable frequency drive controls the motor, or a mechanical fluid coupling. According to the experience of both the mechanical fluid coupling method and the VFD method.

The major differences are:
1. precise speed control from the VFD as opposed to torque control by the fluid coupling. The speed will be determined by the speed torque curve of the driven load.
2. Coupling losses (slip losses) are non existant with the VFD, but can be high with the fluid coupling. The slip loss is equal to the torque times the slip speed. At half speed, the slip speed equals the output speed and so the losses are 50% of the input power.

The VFD is a much more efficient solution allowing for a much greater turn down ratio than you will get with the fluid coupling. Some of these fluid couplings mechanically lock at full load speed which is fine if you are only running at that speed. The VFD coupled system is much more efficient than a fluid coupled system for speed control.

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