What was the biggest change in design for gravity steam systems due to the development of steam traps?

The significant change brought about by the development of steam traps in gravity steam systems relates primarily to the management of condensate. Steam traps are devices that efficiently remove condensate from steam systems while allowing steam to pass through. This innovation improved the effectiveness and reliability of gravity steam systems.

By incorporating steam traps, the system was able to overcome the limitations caused by the old "A" dimension, which refers to the specific vertical drop needed for condensate to flow back to the boiler. The introduction of steam traps ensured that even with lesser gradients or suboptimal layouts, condensate could still be effectively returned to the system without flooding or detrimental backpressure, thus greatly enhancing system performance and efficiency.

In contrast, the other aspects mentioned, while they may relate in some way to the operational changes introduced by steam traps, do not represent the primary change in design functionality. The need for additional venting may come into play with new installations, and using more materials is a practical concern, but these are not reflective of a fundamental change in system design due to steam traps. Instead, the focus on effective condensate return due to steam traps showcases the critical enhancement in gravity steam system design and efficiency.