Rising Stem Gate Valve
Turning the handwheel raises or lowers the valve disc connected to the stem, opening and closing the valve.
Advantages of rising stem gate valves include:
Low fluid resistance, minimal erosion and corrosion of the sealing surface by the medium. Efficient opening and closing.
Unrestricted flow, no flow disturbance, and no pressure drop.
Simple design, short length, excellent manufacturing processability, and a wide range of applications.
Disadvantages of rising stem gate valves include:
Erosion and scratches between the sealing surfaces, making maintenance difficult. Large dimensions, requiring sufficient space for opening, and prolonged opening and closing times. Complex structure.
Non-Concealing Stem Gate Valve
Non-concealing stem gate valves are also called rotating stem gate valves (also called non-concealing stem wedge gate valves). The valve stem nut is mounted on the gate disc. Turning the handwheel rotates the valve stem, lifting the gate disc. The valve stem typically has a trapezoidal thread at its base. These threads and the guide grooves on the disc convert rotary motion into linear motion, converting operating torque into thrust.
When the valve is opened, the fluid flow is completely unobstructed when the disc lifts to a height equal to one times the valve diameter. However, this position cannot be monitored during operation. In practice, the fully open position is defined as the top of the valve stem, the position where it cannot be opened. To account for temperature-induced locking, the fully open position is typically defined as the valve is opened 1/2 to 1 turn after reaching the top. Therefore, the fully open position of the valve is determined by the position (i.e., travel) of the gate disc.
The advantage of this design is that the gate valve maintains a constant height, minimizing installation space and making it suitable for large-diameter or space-constrained gate valves. This design should also include an open/close indicator to indicate the degree of opening or closing.
The disadvantage of this structure is that the valve stem threads are not only unlubricated but also directly exposed to media corrosion, making them susceptible to damage.
What are the main differences between rising-stem and non-rising-stem gate valves?
Non-rising-stem valves have no visible leadscrew, while rising-stem valves do.
The lifting screw of a non-rising-stem flanged gate valve rotates without moving up or down. Only the rod is exposed, and its nut is fixed to the gate disc. Rotation of the screw raises the gate disc, and there is no visible gantry. The lifting screw of a rising-stem flanged gate valve is exposed, and the nut is fixed against the handwheel (does not rotate or move axially). Rotation of the screw raises the gate disc, and the screw and gate disc only rotate relative to each other, without axial displacement. The valve disc appears to have a gate-shaped bracket.
When opening and closing, the steering wheel and valve stem of a non-rising-stem valve are connected and relatively stationary. The valve disc is opened and closed by rotating the valve stem at a fixed point, which drives the disc upward and downward. Rising-stem valves raise and lower the disc through threaded transmission between the valve stem and the steering wheel. To put it simply, the rising stem valve is a valve disc that moves up and down together with the valve stem, and the steering wheel is always at a fixed point.