Protection devices in gas piping systems may include all of the following EXCEPT:

The correct answer is based on the understanding of the roles of various components in gas piping systems. Flow meters are primarily used to measure the flow of gas within the piping system, rather than provide protection. Their main function is to quantify the amount of gas flowing through the system, which aids in monitoring and billing rather than safeguarding against issues such as backflow or excessive pressure.

In contrast, check valves, three-way valves, and shutoff pressure regulators serve protective functions. Check valves prevent the reverse flow of gas, ensuring that gas only moves in one direction and avoiding potential system backdrafts. Three-way valves can control the flow in multiple directions and can be crucial in managing system safety and functionality. Shutoff pressure regulators play a vital role in controlling and maintaining safe pressure levels within the system, preventing overpressure situations that could lead to hazardous conditions.

Therefore, since flow meters do not have a protective role in the piping system, they stand out as the correct answer to this question.