What is the difference between a rising stem gate valve and a non-rising stem gate valve?

Gate valves can be classified by their stem structure as:

Non-rising stem gate valve: The valve stem nut is inside the valve body and in direct contact with the medium. The gate is opened and closed by rotating the valve stem. The advantages of this structure are: the height of the gate valve remains unchanged, so the installation space is small, suitable for large-diameter or gate valves with limited installation space.
This structure requires an opening and closing indicator to indicate the degree of opening and closing. The disadvantages of this structure are: the valve stem threads cannot be lubricated and are directly subjected to medium corrosion, which is easy to damage.
Rising stem gate valve: The valve stem nut is on the valve cover or bracket, and the gate is opened and closed by rotating the valve stem nut to raise and lower the valve stem.
This structure is beneficial for valve stem lubrication, and the degree of opening and closing is obvious, so it is widely used.