This is picture of a B737-800. When you open the bleed system a small amount of air is discharged from this hole (marked with an arrow, lower right). What is it for? And what happens if this hole gets clogged?
AMM Part I Reference 29-09-00, page 3.
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Answering based on ATA 49 system, B757/767 APU Surge Control Valve muscle air plumbing.
Some pneumatic sensing and pressure systems have a moisture bleed hole to prevent icing in the system. They are typically located at a low point or bend in the line to allow water to escape the system while maintaining pressure. If the hole gets plugged it can prevent moisture from escaping and ice to form in the line.
