Experimental investigation of leakage flow measurement and surface morphology in small-scale liquid mechanical seals

This study presents an experimental investigation into the fluid leakage behavior of small-scale liquid mechanical seals, with a focus on precise leakage flow characterization under controlled conditions. An advanced experimental platform was developed to simulate realistic operating conditions, including varying pressures and rotational speeds, enabling accurate assessment of fluid transport mechanisms in mechanical seals. The investigation involved detailed leakage flow rate measurements and surface roughness characterization for two types of seals: a worn seal (3000 h of industrial use) and a new, unused seal. Leakage flow rates were measured using a volumetric collection method to capture flow variations under controlled pressure (up to 12 bars) and rotational speed conditions (up to 6000 rpm). Non-contact surface roughness analysis was conducted using the AltiSurf 500 profilometer, providing 1D, 2D roughness profiles, and 3D surface reconstructions. Results indicate that the worn seal exhibited a lower average roughness (Ra = 0.08928–0.1397 $\mu$m) compared to the new seal (Ra = 0.1203–0.2023 $\mu$m). Despite this smoother surface, kurtosis (Rku) analysis revealed higher peak sharpness in the worn seal (Rku = 13.7611) versus the new seal (Rku = 6.5860), indicating localized surface peaks induced by prolonged operational wear. Leakage flow rate measurements revealed distinct trends. At a constant differential pressure of 4 bars, the worn seal exhibited unstable leakage flow at rotational speeds below 3000 rpm but stabilized at 12.0 mL/h (±0.5 mL/h) above this threshold. Under constant speed conditions (4000 rpm), leakage remained minimal at low pressure differentials ($<$1 bar) but increased significantly beyond 5 bars, marking a transition in leakage mechanisms. The new seal exhibited minimal leakage under all conditions, highlighting the strong correlation between surface evolution and leakage characteristics. These findings provide valuable insights into leakage flow measurement techniques and reveal the influence of surface morphology changes on fluid transport in mechanical seals. The results contribute to improved measurement methodologies and provide guidance for optimizing seal design in aerospace applications.