## 3 Results  
### Implementation of the Developed Experimental Device  
The design of the laboratory test equipment was based on the need of monitoring hydrostatic transducers and the use of ecological fluids in agricultural and forestry tractors operating in ecologically sensitive areas, while input data from operational tests served as a basis for developing the design of the described equipment. Partial results from operational tests, which were published in scientific journals by the authors [16; 17; 18; 19; 20], were used in the analytical solution of the test equipment design. The essence of the technical solution of the proposed test laboratory equipment lies in the fact that the equipment allows based on the selected test to measure the same laboratory equipment flow characteristics of hydraulic pump (1) in the primary (driving) hydraulic circuit (A), flow characteristics of hydraulic pump (3) in the secondary (driven) hydraulic circuit (B), service life of hydraulic pump (1), (3) and hydraulic motor (2) in hydraulic circuits (A) and (B), static and dynamic loading of hydraulic pump (1), (3) and hydraulic motor (2) in hydraulic circuits (A) and (B) and simultaneous testing of physic-chemical properties of different energy carriers in hydraulic circuits (A) and (B). The functional diagram of the laboratory test equipment of hydrostatic transducers and energy carriers in two circuits with an electro-hydraulic proportional valve is shown in Figure 4. The drive of hydrostatic transducers of the laboratory test equipment is provided by an electric motor (5), which is connected to a frequency converter (6) to achieve constant, resp. required speed regardless of the load. The hydraulic circuits (A) and (B) are interconnected by a combined sensor (7), which makes it possible to measure torque and speed. The two hydraulic circuits (A) and (B) can be disconnected from each other, while the possibility of testing the hydraulic pump in the primary circuit remains. The hydraulic circuits (A) and (B) are secured against overload mechanically, by pressure valves (8) and (9) and electrically, by pressure switches (10) and (11). Temperature sensors (12), (13), (14), (15), (16), and (17), pressure sensors (18), (19), (20), (21), (22), and (23), and flow sensors (24) and (25) are equipped in both hydraulic circuits (A) and (B) for sensing operating conditions. To dampen pressure shocks, pressure accumulators (26) and (27) are located in both hydraulic circuits, the actuation of which is ensured by shut-off valves (28) and (29). Throttle valves with stabilization (30) and (31) with control of fluid supply via three-way valves (32) and (33) serve to ensure that the operating temperature is reached or to simulate a higher thermal load of the monitored energy carriers (Figure 4). \begin{table}
\begin{tabular}{c c c} \hline
**Parameter** & **Unit** & **Value** \\ \hline Torque nominal & Nm & 2 \\ Speed rotation maximum & rpm & 12,000 \\ Voltage & V & 10 \\ Voltage in start mode & A & \textless{}4 \\ Voltage in measuring mode & A & \textless{}1 \\ \hline \end{tabular}
\end{table} 
Table 4: Torque sensor HBM stator T12. In the hydraulic circuits (A) and (B) it is possible to connect electro-hydraulic proportional valves (34) and (35) via quick couplings (36), (37), (38), and (39). Electro-hydraulic proportional valves (34) and (35) are used to simulate the pressure load at life tests. In order to provide different types of tests and the possibility of using the hydraulic circuit (A) separately, a separate electro-hydraulic proportional valve (34), (35) and a separate electro-hydraulic proportional valve (36), (37), and (39). Figure 4: Schematic of the proposed laboratory test equipment. tank (46), (47) are designed for each hydraulic circuit (A) and (B). The tanks are equipped with inlet filters (48) and (49) and outlet filters (50) and (51). Coolers (52) and (53) with an electric fan are used to maintain the required operating temperature in the hydraulic circuits (A) and (B).