Created on:2021-10-22 10:31

Railway engineering equipment_ Hydraulic failure of ballast shaping vehicle

Railway engineering equipment_ Hydraulic failure of ballast shaping vehicle

Ssp103 ballast and shaping vehicle introduced by a company from Austria praxay company in 1984 adopts full hydraulic drive. After years of use, it is found that the power of the vehicle is insufficient during ballast distribution and shaping operation. The phenomenon is that when ballast distribution is carried out on both sides at the same time, the operation speed slows down, and finally only one side ballast distribution can work normally. In this way, the work efficiency is reduced by 50%. The on-site operator thought that the system was "weak" due to long service life, wear and increased leakage, and replaced a new pump, but the effect was still not much improved. After careful inspection and analysis, it is found that the pressure of the main hydraulic pump during the operation of the ballast truck is only 26mpa, while the working pressure required by the system should be more than 30MPa. The pressure of the control pump is 3.5Mpa, which meets the use requirements. Therefore, the pressure regulating valves on both sides of the main pump were adjusted, but the pressure still did not increase. It was initially thought that there was a problem with the pressure regulating valve, but no abnormality was found after disassembling the pressure regulating valve. After careful analysis, it is considered that the hydraulic pump control system has failed. Through the analysis of the hydraulic system diagram and relevant data of the hydraulic pump, the cause of the failure is reduced to the pressure shut-off valve (Figure f).

It can be seen from the typical circuit that the pressure shut-off valve is used to limit the flow of the hydraulic pump to a high-pressure function, which is realized by a sequence valve (the pressure shut-off valve in the figure). The valve prevents the action of the high-pressure overflow valve during the acceleration of the possible pressure spike. When the load on the main pump exceeds the set value of the valve, the valve opens to reduce the control pressure from the control pump to the variable piston of the main pump, and the variable piston automatically moves to zero under the action of the spring; When the pump swings to zero and the pressure changes quickly, the high-pressure relief valve limits the maximum pressure. After the pressure shut-off valve is opened, the flow decreases automatically (q = 0). According to this principle, it is considered that the adjustment value of the pressure shut-off valve is inconsistent with the actual working condition of the system, and the pressure adjustment of the pressure shut-off valve is low. When the ballast truck works, when the main pump has not reached the required pressure of the system, it is cut off by the pressure shut-off valve, which limits the increase of working pressure, resulting in the "lack of strength" of the ballast truck and only one side of the ballast can be distributed. Based on this idea, the pressure shut-off valve in the control oil circuit of the main hydraulic pump is properly adjusted. After the operation test, the pressure of the main pump reaches more than 30MPa. When the vehicle is ballasted on both sides, it can still drive at the normal operation speed and accelerate and decelerate freely.

After years of use of the excavation system of the large screen cleaner, it is found that the excavation speed is slower than before, which affects the screening progress of the line. At first, it was suspected that the volumetric efficiency decreased due to the wear and internal leakage of the excavation hydraulic pump. After replacing with a new pump, the excavation speed has not been significantly improved. Therefore, the reason is not the hydraulic pump, but the problem of driving the excavation chain to rotate. However, there are no spare parts in stock, so the test cannot be replaced, because the displacement V of this motor is large (250ml); If one motor is re imported, it is expensive and has a long cycle. The motor can still work, but the efficiency is lower. So, how to use the existing conditions to increase the speed? It is found from the schematic diagram that the excavation motor is a variable displacement motor. From the physical object on site, it is an inclined shaft variable motor. There are adjustment screws on the shell to limit the maximum displacement and minimum displacement. After analysis, if the adjustment screw limiting the minimum displacement is adjusted to the direction of small swing angle to reduce the displacement of the motor, the speed of the motor will increase when the hydraulic pump supplies the same flow, that is, n = q / v. Based on this idea, the excavation motor is adjusted on site, less each time, and the change of excavation speed is observed (not too much to prevent the motor from rotating too fast and causing accidents). After many times of debugging, the excavation speed is much faster than before, and meets the normal use requirements. Therefore, as long as we are familiar with and master the hydraulic working principle of the equipment and understand the structural performance of hydraulic components, we can find an economic and practical method to solve the problem.

Once, there was oil leakage at the end face of the running hydraulic pump of the ballast shaping vehicle. The repairman removed the end cover of the hydraulic pump, took out the damaged sealing ring, replaced it with a new sealing ring, and reinstalled the hydraulic pump. During this process, other parts in the hydraulic pump were not activated, but after the hydraulic pump was connected, it was filled with oil and started the test run. It was found that there was no action and there was no pressure display in the hydraulic pump. This fault is puzzling. For prudence, the hydraulic system was rechecked and no abnormality was found. It can be inferred that the fault still occurs on the hydraulic pump itself. Disassemble the hydraulic pump again and take it to the repair room for disassembly and inspection. It can be seen that the plunger of the cylinder block is well matched, the elasticity of the disc spring meets the requirements, the transmission swashplate is easy and free, and there is no obvious stop part. Reassemble it and install it on the vehicle again, but it is still not easy to use. From the conventional analysis, the hydraulic pump originally worked normally, only because of oil leakage

The sealing ring of the end cover was replaced without moving any other parts, resulting in the situation of "ghost" often said by workers. From the analysis of fault phenomenon, the hydraulic pump has no pressure. Its essence is that there is no flow output. The main reasons for no flow output are as follows: ① serious wear of cylinder plunger; ② The oil distribution plate is seriously worn; ③ Insufficient preload between oil distribution plate and cylinder block; ④ Variable piston stuck at zero position. However, from the process of disassembling the hydraulic pump, items ①, ② and ③ can be excluded, and only item ④ is worth considering. According to this analysis, start to adjust the adjusting bolt of the variable piston to make the swashplate between the maximum and minimum swing angles, and then restart the hydraulic pump. At this time, there is a pressure display immediately and there are all operation actions. Then return the adjusting screw to the original position, and all actions return to normal after the test run. It can be seen that the fault is caused by the variable piston. Although the repairman has not moved the variable piston when replacing the sealing ring, when the hydraulic pump is installed, dirt may be just stuck on the variable piston, and at this time, the variable piston is just in the zero position, resulting in no pressure and flow output of the hydraulic pump.

It can be seen from the above examples that in case of equipment failure, first find out the possible failure parts through principle analysis, and reduce the possible failure causes to a relatively small range; The second is to master the structural performance and adjustment method of each hydraulic element, which is particularly important for troubleshooting on site.

Home    Article    Railway engineering equipment_ Hydraulic failure of ballast shaping vehicle