â—† When the gate valve is opened more than 10%, the axial force, or operating torque, of the gate valve remains relatively stable. However, when the opening is less than 10%, fluid throttling causes a significant pressure difference across the valve. This pressure difference exerts additional force on the gate, requiring a greater axial force to move it, which results in a noticeable increase in the operating torque. Flexible gate valves typically require higher torque near closure compared to rigid gate valves due to their design characteristics.
◆ When the gate valve is closed, the sealing mechanism affects the closing condition. In automatic sealing gate valves (such as flat gate valves), the gate aligns perfectly with the valve seat at full open position. However, this alignment cannot be visually confirmed during operation, so the actual closed position is usually close to the dead center of the valve. The fully closed position for these valves is determined by the gate’s travel rather than the exact alignment. In contrast, forced-sealing gate valves require additional pressure to ensure a tight seal between the gate and the valve seat. This pressure is maintained by the self-locking feature of the stem nut, resulting in higher torque requirements during closing. Therefore, the fully closed position for these valves is determined by the torque applied to the stem nut.
â—† After the gate valve is closed, thermal expansion caused by changes in temperature can increase the pressure between the gate and the valve seat. This increased pressure may make it difficult to reopen the valve, as the torque required to open it becomes higher than the torque used to close it. Additionally, static friction between the sealing surfaces is generally higher than dynamic friction. If the valve remains stationary for a period, the static friction increases further due to temperature changes, leading to a significant rise in the torque needed to initiate movement. This is why some gate valves may feel harder to open after being closed for a while.
Gate Valve Torque Reference Table
Nominal Diameter (mm) | Nominal Pressure (MPa)
---|---
0.25 | 0.6 | 1.0 | 1.6 | 2.5 | 4.0 | 6.4 | 10.0 | 16.0 | 20.0 | 32.0
---|---|---|---|---|---|---|---|---|---|---
50 | 25 | 25 | 50 | 50 | 200 | 65 | 25 | 50 | 50 | 50
600 | 80 | 50 | 50 | 50 | 50 | 1200 | 125 | 50 | 500 | 900
---|---|---|---|---|---|---|---|---|---|---
150 | --- | --- | 1200 | 1800 | --- | --- | 2500 | --- | --- | ---
1800 | --- | --- | --- | --- | 5000 | --- | --- | --- | --- | ---
---|---|---|---|---|---|---|---|---|---|---
--- | 1800 | --- | 5000 | --- | 8000 | --- | --- | --- | --- | ---
--- | --- | 2500 | --- | 8000 | --- | --- | --- | --- | --- | ---
--- | --- | --- | 2500 | --- | --- | --- | --- | --- | --- | ---
--- | --- | --- | --- | --- | --- | --- | 3500 | --- | 6500 | ---
--- | --- | --- | --- | --- | --- | --- | --- | 1800 | --- | 5000
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Note: The torque values provided in the table are based on general experience and are not derived from physical testing or theoretical calculations. They should be used as a reference only.
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