问答题 翻译：There are special types of valves designed to be operated by control instrument rather than by hand.
问答题 翻译：Exploration methods falling in this category are those employing a physical measurement of subsurface conditions made from a surface location.
问答题 翻译：Water and acid gases are removed from the wellhead gas stream because they can cause corrosion and other problems in long distance pipeline and associated equipment.