🔍 Key Concepts

• Torque limit switch function in motor-operated valves • Difference between protecting the motor versus the valve/valve stem • Effect of a foreign object / obstruction on opening vs closing travel

💭 Think About

• When a valve stem is blocked by an obstruction, which component is more likely to be overloaded first: the motor or the mechanical parts of the valve? • In practice, does a torque limit switch usually respond to excessive mechanical resistance (torque) or to position of the valve (travel) – and which failure (open or close) is more critical for damage? • Think about what happens to the current drawn by the motor and the force on the stem when the valve stops moving but the motor keeps trying to turn.

✅ Before You Answer

• Be clear on whether a torque limit is designed to sense mechanical load (resistance) or end-of-travel position • Decide which is usually more expensive/critical to protect: the electric motor or the valve body/stem and seats • Consider whether the same type of damage risk exists when the valve is prevented from opening versus when it is prevented from closing