For discharge piping serving a combination pressure temperature relief valve, the requirement that it must discharge full size to the air gap is critical for several reasons.
Firstly, relieving pressure and temperature safely is essential for avoiding potential hazards such as over-pressurization or explosions in the system. By ensuring that the discharge piping maintains the same diameter as the outlet valve all the way to the air gap, there is no restriction or reduction in flow. This helps maintain the proper functioning of the relief valve by allowing all of the discharged fluid—whether it's water or steam—to exit the system swiftly and effectively without back pressure.
Moreover, discharging full size to the air gap ensures that there is no risk of clogging or blockages, which could occur if the discharge were to be smaller. Blockages can compromise the relief valve's performance, possibly leading to dangerous conditions within the system, which is exactly what the relief valve is designed to prevent.
In summary, the requirement to discharge full size to the air gap is vital for the safety and functionality of the valve and the overall system, emphasizing the importance of effectively managing pressure and temperature within the system.