工况自适应机械密封结构设计与试验

石油化工装置泵用机械密封多为正压单一流体膜设计 ,在装置启动或调节过程中 (过渡过程 ) ,密封腔压力将随装置当时操作条件变化而变化。如果装置抽空操作密封腔出现负压改变了机械密封动静环设计使用条件下的力平衡关系 ,摩擦副轴向可能仅受弹簧力和大气压力作用。如果大气压力作用产生的轴向力大于弹簧力会使摩擦副产生轴向位移 ,造成静环辅助密封圈脱离环座 ,诱发密封失效。过渡过程还可能诱发机械密封端面分离 ,原因在于过渡过程中密封腔压力下降 ,介质气化 ,密封配合面间的流体膜发生相变膜压的合力增大 ,推开密封面 ,也可能使气化后的密封面处于干摩擦状态 ,密封失效。为防止摩擦副整体位移 ,提出了利用波纹管有效作用直径同密封面的内外径相协调的设计结构 ,保证大气压力产生的轴向推力始终与弹簧推力同方向。同时 ,进行了理论分析和试验 ,证明结构可行

The Analysis and Experiment to the Factor of Mechanical Sealfailure Induced b y Press Flactuation

Design parameters of mechanical seal of pump for petrochemical equipment are positive pressure and single fluid film. While starting or adjusting the equipment, the pressure of mechanical seal lumen will alter with the change of operation condition. If the medium in the equipment is evacuated, the seal lumen will be under negative pressure,which alters the dynamic and constant force balance at design condition. Thus,the axial forces in friction pairs are affected only by the spring force and atmosphere force. If the axial force generated by atmosphere pressure is bigger than spring force,the friction pair will move along the axis, which will make the assistant seal loop of rest ring leave away from ring seat and the mechanical seal fails. In the transition state, the pressure in the seal cavity drops,medium evaporates and the phase transition of the fluid film accrues. It will make the total forces increase and push the seal interface away.Another failture reason of seal is that the seal face is in drying friction state when the medium evaporates.To prevent the friction pairs from whole displacement, the design using a structure that makes the effective diameter of tube coordinate with the inside and outside diameter of the seal inner surface is offered, which ensures that the axial force generated by atmosphere is all the time consistent with the spring force in the direction. This structure has proved to be feasible by the theoretic analysis and experiments.