What was the favored operating vacuum level (in inHg) established by the Great Western Railway (GWR)?
Answer
25 inHg.
While most British railways settled on 21 inches of mercury (inHg), the Great Western Railway (GWR) specifically favored a deeper vacuum of 25 inHg, which sometimes caused operational issues when meeting other company locomotives.

Related Questions
How did the vacuum brake system primarily apply the brakes, contrasting with traditional pressure systems?What device, naturally found on steam locomotives, was utilized to create the necessary vacuum for early brake systems?What critical safety issue defined the earliest iteration, the *simple* vacuum brake?Which engineer's name was occasionally used in continental Europe to refer to a variant of the vacuum brake system?What was the favored operating vacuum level (in inHg) established by the Great Western Railway (GWR)?What replaced the steam-driven ejectors for vacuum generation on diesel and electric locomotives?What operational advantage did the vacuum brake system possess over the standard Westinghouse compressed air system regarding brake release?Which engineer focused on refining the mechanical efficiency of the vacuum brake using piston designs via patents secured around 1872?What physical limitation ultimately caused the vacuum brake to decline in favor of high-pressure air systems for heavy, fast trains?What phenomenon caused broken couplings on very long trains when applying vacuum brakes?