High injection pressure is crucial for both modern and future diesel engines, resulting in enhanced performance, fuel efficiency, and reduced emissions. Fuel atomization, combustion optimization, torque control, and engine NVH are among the critical topics directly influenced by the injection strategy. Common rail diesel injection pumps play a pivotal role in delivering fuel at high pressure, with performance metrics such as flow rate and maximum pressure defining the pump’s technology level. Development efforts have consistently focused on improving performance and efficiency since the inception of common rail systems. Future challenges for diesel engines and injection pumps include meeting carbon neutrality goals, which may require adapting to new fuels, engine control strategies (such as hybrid powertrains and drivetrains), and pump drive concepts. In this context, simulating pump operation is essential for optimizing design, predicting performance, and developing control systems. The article deals with the mechanical-hydraulic modelling of a high-pressure pump. The model is based on the lumped parameter simulation of a cylinder-piston pair interacting with intake and delivery volumes via automatically opening valves. Validation of the model relies on dedicated experimental investigation campaigns, enabling measurement of pressure in the pump’s working chamber and high-speed visualization of the intake valve’s position relative to the pump shaft’s angular position. The article reports a detailed description of the model, the experimental approach, and the synthesis of the results.