What is the greatest length allowed for intervening pipe or fitting connecting to a safety valve?

The correct choice reflects industry standards regarding the installation of safety valves, particularly in relation to the length of intervening pipe or fittings. The face-to-face dimension of a corresponding tee fitting is a critical measure because it ensures that the safety valve can operate effectively without restrictions that could impede its performance.

Safety valves are designed to relieve excess pressure and must respond quickly in an emergency. If the intervening piping is longer than the face-to-face dimension allowed, it could introduce unnecessary resistance, potentially leading to a delayed response in the operation of the valve. This dimension is specified to maintain the integrity and reliability of the safety relief system.

Other lengths such as twice the diameter of the valve or three times the valve diameter do not account for the specific design characteristics of fittings that join with safety valves. One foot is an arbitrary limit and may not provide the necessary functionality based on the system design and pressure requirements. Therefore, using the face-to-face dimension of a corresponding tee fitting is crucial for the proper operation and safety of the system.