A pump for pumping fluids in a filtration system is disclosed. The pump has a thrust balancing means to reduce axial loads on motor bearings of the pump during operation of the pump. A drive system of the pump includes an elongate flexible shaft interconnecting a drive shaft and an impeller shaft. The elongate flexible shaft bends and twists to accommodate misalignment during assembly of the drive system. A seal assembly is provided for sealing about a drive shaft. The seal assembly is evacuated to prevent pumped fluid from contaminating fluids in the motor. A concentric coupling and method for making the same are taught which include a cylindrical block which is concentrically bored and cut into an annular L-shaped segment having an L-shaped notch and a semi-cylindrical mating segment which is received into the notch. The coupling concentrically joins a pair of shafts together.
