A pressure regulator also acts as a bypass in case of a blockage in the cooler. A centrifugal pump sends coolant around the external rotor jacketing but via an intricate path in an attempt to even out the massive thermal stresses.
The pressure regulator serves as a backup system for the cooler in case of a blockage.  A centrifugal pump distributes coolant around the external rotor housing, using a convoluted path to manage the intense heat generated.