External gear pumps, capable of delivering high-pressure fluid to propulsion fuel injectors, are widely utilized in aerospace industries. Operating conditions significantly influence the volumetric efficiency and internal leakage of these pumps. This study investigates the effects of rotational speed (2000, 4000, and 6000 rpm) and cavitation number (0.05 to 2) for two distinct side clearances under two outlet pressure conditions. Visualizing the transparent inlet line revealed bubble formation at cavitation numbers below 0.3, depending on operating conditions. The discrepancy between mass and turbine flow rate methods was utilized to monitor severe cavitation. Results indicated that reducing side clearance from 7.5 to 5 microns had a negligible impact on flow rate at cavitation number 1. At numbers below unity, it increased flow rate (3.4% at cavitation number 0.525, 2000 rpm and an outlet pressure of 20 psi), whereas at numbers above unity, it reduced flow rate by suppressing negative side leakage.