A non-displaceable valve member is defined as one that cannot be moved from its seat by a force applied to which part of the valve?

The definition of a non-displaceable valve member is one that remains secured in its seated position even when external forces are applied. In this context, the handle represents the part of the valve that operators interact with to operate the valve.

When force is applied to the handle, a non-displaceable valve member will not budge from its seating, indicating the valve's robustness and reliability in maintaining a sealed position. This characteristic is critical in ensuring that there is no unintended leakage of LP-gas, enhancing safety and operational integrity.

Applying force to the body, nut, or seal does not typically affect the seating of a non-displaceable valve member. The body is the structural component that houses the valve, the nut is usually part of the assembly used to hold components together, and the seal is meant to provide a leak-proof barrier; however, these parts do not directly engage in the operational mechanism of moving the valve member from its seat. Therefore, the interaction with the handle is the key factor in defining the non-displaceable nature of the valve.