Why it happened: We had reused the existing pipework from the old system. It was a mixture of 25mm and 19mm black steel pipe, installed 11 years earlier for a system with a fraction of the current flow capacity. The main distribution line ran from the compressor room along the rear wall of the shop, with a series of branch takeoffs feeding each bay. The entire run was approximately 65 metres of pipe total, with at least 14 right-angle elbows, 6 tee junctions, and two sections where the pipe diameter stepped down from 25mm to 19mm for no apparent reason.
Every 90° elbow is the equivalent of approximately 1–1.5 metres of straight pipe in terms of pressure loss. Every step-down in diameter increases air velocity and friction dramatically. With 62 CFM flowing through undersized pipework with 14 elbows, the cumulative pressure drop was catastrophic — far beyond what any compressor outlet pressure can compensate for.
