Experiment study on auto feeding and jet type drilling nozzle of gas drainage borehole in underground mine

in order to realize an auto feeding and rotary water jet drilig of the in seam gas drainage borehole in the underground mine,the paper had a study to realize an auto feeding and jet type drlig high pressure nzzle.The nozzle had jet orfices set at the forward direction and backward direction of the nozzle.The jetting angle ofthe forward orfice was successively increased.During the jetting drlling operation ,the backward orfice would have a jetting force higher than the forward jting force and the jet water fow had a certain angle along the nozze circumferenia.W ith the hydraulics calculation on the nozzle and the jetting riing experinent of the model under the jet pressure of 30 MPa.the relationship on the jting hole diameter rligspeed and rock sample strength was obtined.The study results showed that the nozzle experiment data and the theoretcal calculation results were wellfited,the auto feeding and rotry j t driling could be released and the average auto feeding force would reach at 63 N. With the pressure bellowed 15MPa.the jtting hole diameter in the rock sample would be over 60 mm and the drilig speed would not be less than 8.16 m/h.The paper had proposalson the further improvement of the nozzle.