Why pressure drop is a chain, not one number
Pressure drop is not a single figure for the plant. It is the sum of losses across dryers, filters, receivers, headers, branches, drops, hoses and couplings, and each one changes with flow. A static reading with no flow tells you very little.
How the audit works
A typical sequence:
- Draw the system and choose measurement points before and after each element
- Log upstream and downstream pressure at the same time with calibrated instruments
- Record flow and compressor state, so each reading can be linked to demand
- Include a representative peak and a typical period of operation
- Compare each segment against the limit set by the process or equipment data
What the results show
The audit can separate:
- Treatment losses: dryers, filters and drains that are restricted or oversized for the flow
- Transmission losses in the main header and ring
- Branch and drop losses to a machine area
- Local losses in hoses, couplings, regulators and tools
- Supply-side limits where the compressors cannot hold pressure at peak
What you receive
A segment-by-segment pressure-drop table, the demand state at each reading, a ranked list of where pressure is being lost, and recommended actions such as element changes, piping changes or control changes. Where a saving is estimated, the assumptions are stated.
Common findings
We often find:
- Filters changed late, with a high differential pressure
- A dryer or filter sized for a lower flow than the plant now uses
- Undersized branches serving large intermittent users
- Raised system pressure used to hide a local restriction
Start with
To arrange the work, please share:
- A simple layout or description of the compressor room, treatment and main piping
- Compressor and dryer details and operating pressure settings
- Operating hours, shift pattern and the problem you are seeing
- Any existing readings, trends or previous audit reports
Frequently asked questions
Why measure under flow?
A restriction only shows up when air is moving. A reading with no flow can look fine while the system performs poorly at peak.
Can I just raise the pressure?
That treats the symptom and costs energy all the time. Finding where the loss occurs is usually cheaper and more effective.
How long does the measurement take?
It depends on the system and the demand cycle. We choose a period that includes a typical peak, and we agree the time with you in advance.
Field guide
Reading a pressure-drop audit: where the bar went
The pressure gauge on the compressor and the pressure at the tool are different numbers. Between them sit the aftercooler, separator, receiver, dryer, filters, header, branch, regulator, hose, coupling and the tool, and each takes some.
One illustrative chain
| Point | Pressure (bar) | Lost here |
|---|---|---|
| Compressor discharge | 8.0 | |
| After treatment | 7.7 | 0.3 |
| Main header | 7.4 | 0.3 |
| Branch | 7.1 | 0.3 |
| After regulator | 6.7 | 0.4 |
| After long hose | 6.2 | 0.5 |
| Tool under load | 5.8 | 0.4 |
The operator says “the compressor is not making pressure”. It is making 8 bar. The loss is in the distribution, and the answer is to fix the chain, not to replace the compressor. Measure at several points under load, starting with the tool and working back.
Typical causes
- Undersized or too-long pipe and hose, sharp bends and restrictive couplings.
- Dirty or saturated filters, undersized dryers and partly closed valves.
- High velocity from pushing too much flow through a small bore. See the pipe-sizing calculator.
The pressure trap
Raising the whole plant to 9 bar because one remote machine is starved makes many devices use more air everywhere (artificial demand) and increases leakage. Better options: fix the loss, boost locally, split pressure zones, regulate at the point of use or give a special load its own compressor. Generate only the pressure the work needs.
Measure energy as specific power
Specific energy = input power ÷ delivered airflow. Lower is better under comparable conditions, but judge it over the real load profile: a machine efficient at full load can be poor if it runs mostly unloaded. An audit should cover demand profile, loaded and unloaded hours, pressure, flow, power, leakage, dew point and compressor sequencing. Try the specific power calculator with your own meter readings.