205 typically the seal ring 235 creates a fluid seal between the flow tube 225 and the stationary sleeve 215 fig3 presents an enlarged cross sectional view of a portion of the safety valve 200 of fig2 the flow tube 225 is more visible here again the flow tube 225 is positioned to maintain the safety valve 200 in its open position this position allows cement or other fluids to flow down through the bore 260 during completion operations and allows hydrocarbons to flow up through the bore 260 during production in either case the flow tube 225 also protects various components of the valve 200 such as the biasing member 210 and the flapper 220 from cement or contaminants that will flow through the bore 260 furthermore the flow tube 225 in the open position prevents the flapper 220 from moving from the open position to the closed position typically the flow tube 225 remains in the open position throughout the completion operation and later production however if the flapper 220 is closed during the production operation it may be reopened by moving the flow tube 225 back to the open position generally the flow tube 225 moves to the open position as the piston 205 moves to the lower position and compresses the biasing member 210 against the spacer bearing 265 typically fluid from the line not shown enters the chamber 245 thereby creating a hydraulic pressure on the piston 205 as more fluid enters the chamber 245 the hydraulic pressure continues to increase until the hydraulic pressure on the upper end of the piston 205 becomes greater than the biasing force 210 on the lower end of the piston 205 at that point the hydraulic pressure in the chamber 245 causes the piston 205 to.