Torque control with a slip device for pressure testing a hydraulic fracturing system

A hydraulic fracturing system, comprising:

• one or more fluid conduits;
• and
• a hydraulic fracturing pump system fluidly coupled to the one or more fluid conduits, the hydraulic fracturing pump system comprising:
• a hydraulic fracturing pump;
• a gaseous fuel engine configured to drive the hydraulic fracturing pump;
• a torque converter comprising an impeller clutch that selectively couples the hydraulic fracturing pump with the gaseous fuel engine;
• a gear system mechanically coupled to the hydraulic fracturing pump between the hydraulic fracturing pump and the torque converter;
• and
• a controller configured to cause, in connection with a pressure test for the hydraulic fracturing system, a slip engagement of the impeller clutch to control an output torque to, and a discharge pressure of, the hydraulic fracturing pump.