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

Characteristics for rising stem gate valve: 

The valve stem trapezoidal thread of the rising stem gate valve is placed outside the valve body, and is located on the upper part of the valve stem. By rotating the valve stem nut, the valve stem drives the valve disc to go up and down synchronously to realize the opening and closing of the gate valve, so it is easy to identify the opening and closing state of the gate valve, to avoid the misoperation; Since the valve stem nut is placed outside the body cavity, which is conducive for lubrication, and the opening and closing state of the gate valve is intuitive and obvious, so the rising stem gate valve is widely used; but in harsh environments, the exposed thread of the valve stem is easily damaged and corroded, and affects the operations; the disadvantage of the rising stem gate valve is that the height of the rising stem gate valve after opening is large, and a stroke is usually added on the basis of the original height of the gate valve, so the rising stem gate valve requires a larger operating space. 

Characteristic for non rising stem gate valve: 

The non rising stem gate valve is also called a rotating stem gate valve. The stem nut is placed inside the valve body, and is connected direct with the medium, and is often fixed on the valve disc; Through the rotation of the valve stem, the stem nut drives the valve disc to move up and down to complete the opening and closing of the gate valve. Usually, there is a trapezoidal thread at the bottom end of the valve stem and the guide grooved on the valve disc, the rotary motion is changed into a linear motion, that is, the operation torque is changed into the operating thrust; since the trapezoidal thread for driving is placed inside the valve body, it is easy to be corroded by the medium and not convenient for lubrication, the opening degree cannot be directly observed, so an additional indicating device is required. However, its valve stem does not move up and down, so the required operating space is small, the non rising stem gate valve is suitable for occasions where the installation space is limited and the pipeline is dense.