Rainfall simulation is widely used in the laboratory and in field work to produce artificial rainfall for small-scale surface hydrology and soil erosion studies. Simulated rainfall produced by simulators must be predictable, accurate and consistent to be useful to model the related physical processes. Pressure fluctuations in the water supply system frequently cause variation in rainfall intensity during simulated events. This study describes a hydraulic system that is attached to the outlet (nozzle) of a rainfall simulator to ensure constant pressure and discharge, which consequently facilitates constant rainfall intensity at ground level, throughout the rainfall event, especially in the controlled environment of the laboratory. Fifty rainfall events were simulated (five different pressure levels at the water intake). More than 750 pressure measurements were collected for each rainfall event at the water intake and at the nozzle, adding a total of more than 75,000 pressure measurements. Standard deviation of pressure measured at the water intake was always higher than at the nozzle (ranging from 1.978 to 4.199 times higher). The results show that with this hydraulic system rainfall simulators can operate with constant (rainfall) intensity throughout the entire simulation or sequence of events, even if the water supply pressure fluctuates.