While dry-running and dry-run-like symptoms can be detected with a drop in motor loading (current), other pump failure modes can result in increased motor loading. A common cause for increased loading could be abnormally low temperatures in the winter, increasing the S.G. and viscosity of the chemical.

Other causes could mean the pump is already damaged and should be stopped immediately to prevent further damage. For magnetic drive pumps, increases in loading could mean that there are factors obstructing the rotation of the impeller. Examples could range from crystallization of the chemical, chemical coating of the chemical, excessive wear/roughening of the rotating parts, abnormal contact between rotating parts with the pump structure, etc. The step to check for obstruction on a pump with a fan-cooled induction motor is to shut down the pump and use a thin wire to manually rotate the cooling fan. If the fan cannot be rotated or it takes great effort to rotate the fan, there is excessive contact or friction within the pump. Do not continue to run the pump and schedule for a service agent to dismantle and check the pump. Canned motor pumps may not have an external cooling fan and are generally not customer serviceable. If your canned motor pump is experiencing increased loading, please contact the manufacturer or its service agents for assistance.

For magnetic drive pumps, rotational energy from the motor is transmitted to the pump via a magnetic coupling. Since the magnetic couplings are not in physical contact, if the rotor of the pump (impeller and inner magnet) is jammed and could not move, it is possible that the external (drive-side) magnet could still rotate. This phenomenon is called decoupling. In addition to the pump rotor being rendered immobile, other factors could also lead to decoupling.

Operating the pump at the extremes of the pump curve. At the extremes, either at low flow or at very high flow, the starting torque could exceed the designed safety margin of the magnetic coupling. Once the magnets decouple, they cannot recouple during operation due to the high rotation speeds. In such a scenario, it is advisable to perform a soft start of the pump either through a VFD or using a soft starter.

For chemicals with increased viscosity during winter, it is possible to restart the pump with a shut-off discharge valve. This lowers the loading of the motor, allowing the pump to start moving and overcome the inertia. Once the pump is up to speed, slowly open the discharge valve to gradually increase the load of the pump. In this case, make sure not to overload the motor.