Hydraulic rodless drainage system based on PLC
                                                                                             XU Qi
                         （College of Electrical Engineering and Control Science, Nanjing Tech University, Nanjing 211816, China）

Abstract: Aiming at the problems of high labor intensity of staff, low efficiency of equipment and poor control precision in rodless drainage of coalbed methane, a new type of hydraulic driven rodless pump was designed, and the control system was designed based on PLC. The designed control system measured the bottom hole flow pressure in real time by pressure gauge, and feed the measured value back to the PLC to compare with the set value. Based on the results of the comparison calculation, the motor speed was adjusted in real time by frequency converter, and then the bottom hole flow pressure was adjusted dynamically. The rodless pump was driven by a threechannel tubing with a power hydraulic pipe pressurized and reciprocates under the driving force. Motion, to achieve automatic up and down switching between the valve body, effectively reduced the labor intensity of staff. The test results show that the system can adjust the bottom hole flowing pressure quickly and accurately according to the set value, and has a small overshoot.

Key words: coalbed methane; drainage system; rodless pump; bottom hole flow pressure; speed control