1. Definition and characteristics of opening and closing torque
The opening and closing torque of a floating ball valve refers to the torque value required to drive the valve stem to rotate 90° to complete full opening or full closing. Its maximum value usually occurs at the final closing moment or the initial opening moment, which is mainly affected by the medium pressure, valve seat friction and fluid dynamic resistance. The torque characteristic curve shows that the torque is asymmetrically distributed with the opening degree during the opening and closing process, and the swirl effect is significantly reduced when the valve is close to full opening or full closing.
2. Specific torque value range
The opening and closing torque of the floating ball valve varies significantly with the nominal size (DN) and pressure level (PN):
Low-pressure small-diameter scenario (such as DN15, PN1.6 MPa):
The opening and closing torque is about 3-5 N·m, which is suitable for manual operation scenarios;
Medium-pressure conventional-diameter scenario (such as DN50, PN4.0 MPa):
The torque range is 50-250 N·m, and a worm gear or light electric actuator is required;
High-pressure large-diameter scenario (such as DN200, PN40 MPa):
The torque rises sharply to 1500-4800 N·m, and a high-torque electric/pneumatic actuator must be used. Some extreme working conditions require hydraulic drive.
3. Key influencing factors
Medium pressure (PN):
The torque is approximately positively correlated with the pressure. For example, the torque of a DN80 ball valve is 80 N·m at PN16, and increases to 400 N·m at PN40;
Valve seat friction coefficient:
The friction torque of a soft seal valve seat (PTFE) is 30%-50% lower than that of a metal hard seal, but performance degradation may occur at high temperatures;
Diameter (DN):
The torque increases exponentially with the diameter. The opening and closing torque of a DN100 ball valve is about 4-6 times that of a DN50.
4. Design and Selection Notes
Actuator Matching:
When selecting an actuator based on the calculated torque value, a 20%-30% safety margin should be reserved to avoid overload failure;
Operation Frequency Limit:
For high-frequency opening and closing conditions (such as >30 times per hour), the valve seat lubrication structure needs to be optimized to prevent overheating and wear of the sealing surface;
Special Medium Treatment:
Particle-containing or high-viscosity media may cause the actual torque to exceed the standard value by more than 50%, and a scraped valve seat or increased drive power is required.
Summary
The opening and closing torque range of floating ball valves is from 3 N·m (DN15/PN1.6) to 4800 N·m (DN200/PN40). The selection requires a comprehensive evaluation of pressure, caliber and medium characteristics, and actuators with a flat torque curve are preferred to reduce impact loads. It is recommended to configure a torque protection device for large-caliber high-pressure valves to prevent equipment damage due to jamming or overload.
