Created on:2021-04-24 09:07

Trouble shooting of pv18 electro hydraulic servo bidirectional variable axial piston pump difficult to start

Trouble shooting of pv18 electro hydraulic servo bidirectional variable axial piston pump difficult to start

① The pv18 electro-hydraulic servo bidirectional variable axial piston pump is the main hydraulic pump of the hydraulic system of the asbestos cement pipe rolling forming machine produced by RVA company of the United States. It indirectly controls the pressing force of the roller device by controlling the oil discharge pressure of the variable pump. Pv18 pump is the core component of the whole system. The structural principle of the pump is shown in Fig. g. it is mainly composed of plunger pump body 9, servo cylinder 8 and control box 2 [electro-hydraulic servo valve 13 and position detector (LVDT) 3 mechanically connected with cam trunnion 5 and swashplate 6]. The electric control cabinet matched with the pump is equipped with servo amplifier and pump control analyzer. As can be seen from figure h, the PV pump is also equipped with hydraulic components such as double relief valve group 2, relief valve 3 and relief valve group 4 of double check valve. When the pump is working, the control pressure oil enters into the electro-hydraulic servo variable mechanism (servo) of PV pump through oil passage 9 from oil port C, and changes the flow and direction of the pump by changing the inclination angle of swash plate; the control pressure is set by relief valve 3; the swash plate position can be observed and fed back to the signal end through the mechanical indicator connected with LVDT; the double relief valve group 2 provides two-way safety protection for PV pump; the additional make-up pump can pass through the oil pump Port s and valve group 4 fill and replenish oil to the hydraulic system driven by PV pump; the low pressure oil discharged from valve group 4 and valve 3 can cool the friction pair in the pump and wash the wear materials through oil passage 6 and orifice 7, and mix with the oil discharged from the pump and return to the oil tank from leakage oil pipe 8; valve 5 is a one-way back pressure valve. The rated pressure of PV pump is 12MPa, the rated flow is 205l / min, the rated speed is 900r / min, the driving motor power is 18kw, the control pressure is 3.5Mpa, and the control flow is 20L / min. PV variable displacement pump is essentially a closed-loop electro-hydraulic position control system, and its control principle block diagram is shown in Figure I.


② Cause analysis, troubleshooting and effect PV pump generally works well, but sometimes it is difficult to start or even can not start at all.


At first, we tried to increase the control signal (increase the circuit gain), but it failed. After careful analysis, it is believed that the working environment of asbestos cement pipe crimping machine and its hydraulic system is bad, and there is a lot of dust, which is easy to pollute the oil of the hydraulic system, thus causing the blockage and jamming of the electro-hydraulic servo valve in the PV pump. It was found that there were a lot of ferromagnetic substances and nonmetallic impurities around the servo valve, and the fault was eliminated after cleaning. Further analysis found that the control oil circuit of the pump had been equipped with a filter with 10 μ m filtration accuracy, but such a problem still occurred, indicating that the filter used had too low filtration accuracy to meet the requirements. Therefore, it was better to replace the filter with a 5 μ m paper filter with pollution.

(6) Cycloid motor output powerless fault and troubleshooting

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