What can all steam traps allow to pass through them?

The selection of dirt, air, and condensate as the correct answer relates directly to the function of steam traps within a steam system. Steam traps are designed to remove condensate, air, and other non-condensable gases from the steam system while preventing the escape of steam.

When steam is generated, it releases heat energy, and as it travels through the piping system, it cools and condenses back into a liquid form (condensate). This condensate must be drained away to maintain efficiency and prevent water hammer, which can occur if condensate accumulates. Additionally, air and other non-condensable gases can cause inefficiencies and should also be removed from the system to ensure optimal operation.

It is essential for steam traps to allow these substances to pass through, as their presence can significantly affect the performance and safety of the boiler system. The other options do not accurately describe the primary function of steam traps, as they do not allow excessive steam or pressure to pass through, nor are they intended to manage heat directly in terms of excess heat transfer. Thus, recognizing that steam traps specifically facilitate the passage of dirt, air, and condensate is crucial for understanding their role and ensuring efficient boiler operation.