ABSTRACT Vertical pump systems are vital in industries like water treatment, power generation, and oil and gas production. Their efficiency depends on well-designed components, especially the main shaft connecting the motor to the pump impeller. Changes in shaft length greatly impact vibration, structure, and overall performance. Therefore, thorough evaluation of shaft length modifications is crucial for ensuring equipment suitability and long-term reliability. This study examines how changing shaft length in a vertical pump system, from 70 cm to 170 cm due to construction constraints, affects its performance. Using Finite Element Analysis (FEA), the study evaluates both shaft designs’ natural frequencies, critical speeds, and maximum stresses. Results reveal that the 170 cm shaft design is unsuitable, leading to increased stresses and a higher risk of vibration-induced failures compared to the original design. These findings stress the importance of controlling design parameters and conducting thorough analyses before implementing modifications to ensure reliability and operational stability. Unplanned design changes like shaft length modifications can severely impact pumping equipment performance, emphasizing the need for careful consideration and analysis prior to implementation. This research emphasizes the importance of considering shaft length in the design of vertical pump systems to ensure reliability. The findings offer valuable insights for engineers and designers to maintain long-term operational stability and performance. Ultimately, this improves safety and efficiency in industrial and municipal processes reliant on these pump systems.