Final answer:
Replacement tubing should be cut longer than the original 15 inches, considering extra length for buffer space, which may be up to 8 diameters side-to-side and 15 diameters deep based on tube diameter.
Step-by-step explanation:
When replacing a 15 inch long fluid line, the appropriate length to cut the replacement tubing depends on the specific application and context. The older "rule of thumb" for buffer space around tubing was 5 diameters side-to-side and 7-8 diameters deep.
However, more recent suggestions for safety and efficiency specify as much as 8 diameters side-to-side and 15 diameters deep.
If these guidelines refer to the minimum straight length required at the end of a tube before any bends or connections, and your tube diameter is 1 inch for example, you would need an extra 8 inches on each side. This would mean cutting the tubing at 31 inches long: (15 inches + 8 inches + 8 inches).