6055 with 7091 controller

[mistaflicksta]

I have two 6055 pumps and two 7091 controllers. On one of them when I adjust the power on the controller, one on high and the other one on low. The pump comes to a complete stop on the low alternation. I have to set the power on both knobs to relatively the same power for the pump to work constantly. I switched controllers and the same thing happens. Is there something I am doing wrong?

 

[rvitko]

My guess would be the pumps are dirty or worn, check the drive units, if the drive unit 6055.700 is sticking to the metal shaft by calcium deposits or debris, at low speed there is not enough power to overcome the resistance and keep them spinning.