# Identification of the Wear Margin of a Pipeline-Machine Subsystem
## 6 Results and Discussion  
The lubrication subsystem of a ship's main engine may be considered as an open pipeline-machine subsystem. It was stated in Section 2 that the wear margin of an open subsystem is not exhausted if the subsystem delivers fluid to the destination with capacity \(\dot{V}\) falling within the range \(\dot{V}_{2}-\Delta\dot{V}_{2}\), at pressure \(p\) in the range of \(p_{2}-\Delta p_{2}\) and temperature \(T\) in the range of \(T_{2}-\Delta T_{2}\). This means that the fluid pressure and volume flow rate should be measured during operation. It follows from the author's research that no such control may cause machine and sealing failures. The lubrication subsystem of a ship's main engine was examined as it had been producing excessive levels of noise and vibrations. In normal operation, due to investment costs, the lubrication subsystem is expected to supply an engine with oil of temperature and pressure within required ranges of values. The real value of the pressure depends on oil flow resistance in an engine and on the volume flow rate of oil delivered to the engine, while an excessive value of oil volume flow rate is not harmful for the engine. The volume flow rate of oil produced by the pump is divided into that delivered to the engine and that returning to the pump suction pipe. It was found that during the oil flow rate division where the pressure at the engine inlet was close to the maximum required value, the pressure \(p_{d}\) at pump discharge (Figure 1) exceeded maximum values for the sealing used in the pipes (oil leaks) and for the pump used. The examined subsystem was equipped with a screw displacement pump. Positive displacement machines are equipped with overload relief valves that open if a specific pressure is exceeded, which occurred in the examined case and resulted in opening and closing of relief valves, increased noise, damage to valve elements and drops in volume flow rate. It was also found during the tests that in similar ships, where the pressure on the engine inlet was maintained in the lower range of required pressure, no excessive vibrations of the pumps and no higher frequency of failures of lubricating subsystem elements were observed. Therefore, engine lubrication subsystems seem to need two things: the determination of the required oil flow rate and the measurement of this oil flow rate. Due to the lack of recognized identification methodology applicable to a pipeline-machine subsystem with a closed vessel at the end of the discharge pipe, tests were performed to ascertain practical reality and plausibility of the methodology proposed in Section 5. Tests were conducted on industrial and laboratory subsystems with closed vessels at the end of the discharge pipe. The tested subsystems were equipped with sets consisting of a piston displacement machine (with piston-crank mechanism), belt transmission and electric motor. The time of vessel filling was measured as the working time of the machine (motor on/off time). The pressures were read out after the machine was switched off and the indications stabilized. Measurements were performed using the devices normally installed on the examined subsystems, while the electric power and energy was measured by the HT4022 tester. The tester enabled power and energy measurement on three phase-balanced systems. Electric energy could be measured with 1 Wh accuracy. The tests were conducted on two different subsystems, with one being a compressor with a pressure vessel and the other being a pump with a hydrophore. In the former case, due to the inability to measure temperature, only the efficiency of filling the vessel was determined. The filling efficiency of a subsystem was determined for a 0.4 m\({}^{3}\) air vessel and an air compressor of 80 m\({}^{3}\)/h capacity, driven by an 11 kW electric motor. Pressure in the vessel was measured by a manometer.