An operational test and degradation analysis of a hydraulic fluid based on synthetic esters was performed in three types of work machines. To enhance its performance, ZDDP anti-wear agents were added. Hydraulic fluids are susceptible to degradation by oxidation; therefore, to ensure the long service life of the equipment, it is essential to monitor their current condition through laboratory analyses during machine operation. Emission spectrometry was used to determine the presence of contaminants and the concentration of additive substances in the oil. Pollution was assessed by cleanliness code analysis according to ISO 4406-2021, alongside Total Acid Number (TAN) analysis and LNF analysis of wear and contamination in lubricants. The combination of cleanliness code analysis and LNF analysis of particle type and origin allows for monitoring not only the count but also the origin of contaminating metallic particles, which increases the probability of correct diagnostics and successful detection and resolution of wear problems. All three machines were still operational at the end of the test interval, meaning the tested hydraulic fluid is a suitable alternative to mineral variants. However, in all three pieces of equipment, it is necessary to replace the hydraulic fluid and flush the system before further operation. Furthermore, we recommend replacing the filter elements and inspecting the internal spaces of rotating parts with an increased potential for wear. From the oil’s perspective, it is advisable to add more anti-wear additives (ZDDP), which are depleted the fastest.

This paper presents an experimental investigation into the flow characteristics and volumetric efficiency (η_vol) of a fixed-displacement external gear pump (GHD 17R) operating under coupled hydraulic parameters. Measurements were performed on a single-circuit hydraulic test rig within rotational speeds of 500–2500 min^-1, operating pressures of 2–10 MPa, and fluid temperatures of 30–60 °C using a biodegradable synthetic ester-based hydraulic fluid (48 mm²·s^-1 at 40 °C). To handle flow fluctuations caused by structural vibrations around 1250 and 1750 min^-1, a 15% trimmed mean statistical filter was successfully implemented. Experimental 3D flow and efficiency maps were constructed using Matlab. To determine the driving factors behind pump performance variation, a sensitivity analysis based on absolute, normalized, and relative significance was proposed and compared against a three-way analysis of variance (ANOVA) effect size model (η² and partial η²). The relative sensitivity approach identified rotational speed as the dominant parameter for direct hydraulic flow, contributing 95.80%, whereas pressure and temperature contributed 1.88% and 2.32%, respectively. In contrast, when focusing on volumetric efficiency, the proportional impact of speed was removed, revealing a balanced distribution of losses: rotational speed contributed 54.73%, temperature 26.08%, and pressure 19.19%. The three-way ANOVA confirmed that all factors and their interactions had a statistically significant effect (p < 0.05). The minor discrepancies between relative sensitivity and ANOVA effect size (η² = 10.24% for pressure vs. 3.98% for temperature) were attributed to coupled parameter interactions, which are successfully uncoupled by ANOVA. The findings demonstrate that a concurrent evaluation of both actual flow and volumetric efficiency maps provides critical information for advanced diagnostic, control, and optimization tasks in modern fluid power systems using eco-friendly fluids.

This paper presents an experimental investigation into the flow characteristics and volumetric efficiency (η_vol) of a fixed-displacement external gear pump (GHD 17R) operating under coupled hydraulic parameters using an eco-friendly synthetic ester-based hydraulic fluid (48 mm²·s⁻¹ at 40 °C). Measurements were performed on a laboratory single-circuit hydraulic test rig across a rotational speed range of 500–2500 min⁻¹, operating pressure range of 2–10 MPa, and fluid temperature range of 30–60 °C. To eliminate flow fluctuations caused by structural vibrations at 1250 and 1750 min⁻¹, a 15% trimmed mean statistical filter was successfully implemented. A comparative sensitivity analysis—evaluating absolute, normalized, and relative significance—was developed and compared against a three-way analysis of variance (ANOVA) effect size model (η² and partial η²). The relative sensitivity approach identified rotational speed as the dominant parameter for direct hydraulic flow, accounting for 95.80% of total variation. Conversely, when evaluating volumetric efficiency, the proportional impact of speed was removed, revealing a balanced distribution of internal losses: rotational speed contributed 54.73%, fluid temperature 26.08%, and pressure 19.19%. The three-way ANOVA confirmed that all primary parameters and their cross-interactions had a statistically significant effect (p < 0.05). The findings scientifically demonstrate that temperature-induced viscosity collapse exhibits a stronger relative dynamic sensitivity on volumetric losses than pressure fluctuations within standard operating envelopes. The constructed multi-dimensional flow and efficiency maps provide practical input for advanced diagnostic tools, real-time thermal condition monitoring, predictive maintenance, and energy-optimized control schemes in modern fluid power systems using eco-friendly lubricants.