Gate valve is a kind of valve for medium connection and shut- off but not suitable for regulating. Compared with other valves, gate valves have a wider range of combined applications for pressure, service fluid, design pressure and temperature. According to the screw position of the stem, the gate valve can be divided into rising stem gate valves and Non-rising stem gate valve (NRS).
Stem nut for open stem gate valve is on its cover. Rotation of stem nut drives stems up and down when opening or closing gate valve. It opens and closes the disc connected to the stem by lifting or lowering the thread between the handwheel and the stem and fully open position does not disrupt the flow. This design is favorable to the lubrication of the valve stem and has been widely used. The wedge is rubber coated and It is not used as a check valve and flow rate adjustments.
The advantages disadvantages of rising stem gate valve：
- Easy to open and close.
- Small fluid resistance, sealing surface by medium erosion and erosion.
- Medium flow is not restricted, no turbulence, no pressure reduction.
- The sealing surface is easy to be eroded and scraped, difficult for maintenance.
- Larger structure requires more space and long-time opening.
Non-Rising Stem means outside stem, also referred to as the rotary stem gate valve or blind stem wedge gate valve. In an NRS valve, the stem will turn to open and close the gate, but the stem does not move up or down as it turns. As the stem turns, it moves into or out of the valve, which also moves the gate to open or seal the valve.
The advantages and disadvantages of non-rising stem gate valve：
- Non-rising stem valves take up less space, ideal for gate valve with limited space. Generally, an open-close indicator should be installed to indicate the degree of open-close.
- Failure to lubricate stem threads will result in medium erosion and easy damage.
What’s the difference between rising stem gate valve and non-rising stem gate valve?
- Appearance: The rising stem gate valve can be seen from the appearance whether the valve is closed or open. The lead screw can be seen while the non-rising stem gate valve cannot.
- The ascension screw of rising stem flanged gate valve is exposed outside, the nut cling to the handwheel is fixed (not rotating axial movement), the rotation of the screw and gate only relative motion without relative axial displacement of the disc and stem up and down together. The lifting screw of the non-rising stem flange gate valve only rotates and does not move up and down.