Torque calculation for ball valves
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I often encounter problems related to the calculation of torque for ball valves, which can be electric or pneumatic. However, the values I calculate myself differ significantly from those obtained by referring to tables provided by manufacturers, as the torque level directly affects the choice of actuator, which in turn influences the cost. I would like everyone to discuss which formula yields the most accurate results.
I used the formula mentioned above to make the calculations, and the results were very different from those provided by the manufacturer. For example, for a ball valve with a diameter of 500 and a pressure of 300 LB, using a pneumatic fixed soft-seal ball valve, the manufacturer specified a torque of 12,500 N.m, while my calculation gave 6,500 N.m. Why is there such a big difference? The prices of pneumatic actuators vary by tens of thousands! Unacceptable
This question can be answered from several aspects: 1. Different sealing methods are used in the design, which results in different calculated torques. 2. The torque calculated according to the API6D standard must be multiplied by 2
I forgot to tell you that many ball valve manufacturers copy each other’s samples, which is why problems arise
I’ve learned it, but I just don’t know which specific calculation is the correct one!
Method for calculating valve torque: The torque of a valve is calculated as follows: half the square of the valve’s diameter multiplied by 3.14 to obtain the area of the valve disc; this value is then multiplied by the pressure it can withstand (i.e., the operating pressure of the valve) to get the static pressure acting on the shaft. This value is further multiplied by the friction coefficient (for ordinary steel, the friction coefficient is 0.1, while for steel against rubber it is 0.15), and finally multiplied by the shaft diameter divided by 1000. The result gives the torque of the valve, expressed in Newton-meters. For electric actuators and pneumatic actuators, a safety factor of 1.5 times the valve’s torque should be used
Okay, not bad at all, thanks to the original poster for sharing
The actual valve torque is always greater than the calculated value, and in some cases it is much larger.
Learning *new knowledge again: handshake
The following are my personal opinions. If the valve manufacturer is a reputable one, then the torque values provided by the manufacturer should be used as a guide for selection, as they represent the manufacturer’s test data. If the manufacturer is not reliable, then more factors need to be taken into consideration, and it’s advisable to use a higher safety factor
Torque still needs to be measured physically; it’s not easy to calculate it accurately using design formulas, as these formulas involve many coefficients, most of which represent ranges. Choosing either the higher or lower value for these coefficients results in significant differences in the torque value.