It appears only when air flows
In a closed network with no demand, pressures may nearly equalise even if a connection is undersized. Loss increases as flow rises, often more than linearly in turbulent flow. The exact relationship depends on density, friction, flow regime and geometry. A single static reading will not reveal the cause.
Locate the resistance
Measure simultaneously before and after the suspected component under relevant load. Distinguish persistent loss from a brief dip during rapid demand. Pipework calculation includes length and local resistance, but without actual regulator or filter data it does not model the whole station.
What to check in practice
- Record pressure at the source, on the main line and at the consumer.
- Check quick couplings, hoses and clogged filters, not just the main pipework.
- After intervention, verify pressure under the same or more demanding operating conditions.
Example scenario
Under demand, pressure is 7.2 bar(g) before a filter and 6.8 bar(g) after it: a difference of 0.4 bar. If pressure at the machine is simultaneously 6.2 bar(g), another 0.6 bar is lost downstream. Raising compressor pressure would merely mask part of the problem.
What to watch out for
- Comparing readings from different times and demand levels.
- Adding atmospheric pressure to a pressure difference.
- Attributing every pressure drop to an undersized compressor.
Is the lowest velocity always the most economical?
Larger pipework usually reduces pressure loss but increases investment. The aim is to balance allowable pressure drop, peaks, future expansion and cost. Selecting solely by one recommended velocity value is insufficient.