... , tubing string and sealing layers between the casing and tubing the annular space between, and control production wellhead pressure and regulate oil ( ... also be used for acid fracturing, water injection, testing, and other special operations. Product specifications Rated pressure2000~20000PSIProduct specification levelPSL ... ,BB,CC,DD,EE,FFApply MEDIAOil, gas, mud, etc API 6A wellhead christmas tree