Yes, the mesh was not conencted i have used node merge to fix the problem. Thank you so much. I want to ask one more question: how can i apply pressure on the external face of this cylinder. This is a line model so i can't choose the external face to apply pressure. I'm thinking using the line pressure but i dont know if it will apply to all the model not just the external face and i can't manage to have a normal pressure with line pressure. Can you help me with this problem?