Tunnel boring machine is characterized by harsh underground working condition, severe vibration, large impact load and bad maintenance condition.  For hydraulic cylinders, they are key component of the machine, we put highest requirement on the reliability of them because any cylinder failure will bring huge loss to the whole project. Hengli carried out a lot R&D works on coatings, sealing, support ring and mechanical structure,The special nickel-chrome coating has better vibration and corrosion resistance capability than chrome coating. For the propulsion cylinder, the lateral force is extremely big due to eccentricity structure, our special designed guide bush welded with copper alloy proved to be a good solution. Our FEA engineer help optimize each cylinders structure so as to improve strength and reduce weight.The exciting news of successful tunnel project comes one by one is best proof of our reliable quality.