What is pressure profiling and why does it matter?
Most plants judge pressure from one gauge in the compressor room. That gauge tells you what the compressor makes, not what a packaging machine 150 metres away receives during a shift change. A pressure profile replaces that single number with a picture of the whole system over time.
The usual reaction to a low-pressure complaint is to raise the compressor setpoint. That is expensive. As a typical rule, every extra bar of generated pressure costs about 7% more compressor power, and higher pressure also increases leakage and unregulated consumption across the plant. If the real problem is a clogged filter, an undersized drop line or a slow-reacting control band, a higher setpoint only hides it.
A profile answers four practical questions:
- What pressure does each critical user need, at its inlet, during its worst operating event?
- How much pressure is lost in each segment: treatment, header, branches, drops, hoses and regulators?
- How does the supply side behave as demand changes: load/unload bands, VSD response, sequencing and receiver storage?
- Is a complaint caused by sustained low pressure or by short dips that only fast logging can see?
Start with the requirement at the right point
Before any logger goes in, define what “enough pressure” means. A minimum pressure is incomplete unless it states the location and the flow condition. “6 bar” at a header is not the same as “6 bar (87 psig) at the cylinder valve inlet while the machine is cycling at full speed”.
For each critical consumer, record:
- The measurement point: machine inlet, regulator outlet, tool connection or another specified point.
- The minimum pressure and the event during which it applies, such as start-up, full-speed cycling or a cleaning blow-off.
- Where the figure came from: the equipment manual, a documented trial, or a habit or assumption still to be checked.
- What happens when pressure is too low: lost force, slower cycles, product rejects, a control fault or a safety interlock.
Separate a machine’s genuine requirement from a regulator that was simply turned up years ago. Many plants find that the “required” pressure is a setting no one can explain.
Where should the measurement points go?
Choose points that split the system into segments you can interpret. Too few points leave the location of a loss unclear. Too many badly chosen points produce data without a decision.
| Point | What it shows | Typical finding |
|---|---|---|
| Compressor discharge or common header | What the supply side generates and how its control band behaves | Wide load/unload band, poor sequencing between machines |
| Dryer and filter inlet and outlet | Loss across air treatment | Loaded filter elements, undersized or bypass-valved dryers |
| Receiver connection | Whether storage is actually usable | Receiver piped as a dead leg, isolated or too small for peaks |
| Main header ends and ring junctions | Distribution loss and flow path | Undersized headers, long runs, restrictive valves |
| Branch take-offs and drops | Local restrictions | Small drop lines, quick couplings, long hoses |
| Critical machine inlets | What the user actually receives | Short dips during cycling, regulator droop |
Mark every point on a current piping diagram together with valves, regulators, storage and cross-connections. In a ring main the flow path can change with demand or isolation, so two readings are not always a simple series pressure drop. Note any parallel feed or regulator between them.
How do you take measurements that can be trusted?
Pressure loss across a segment must be worked out from upstream and downstream readings taken at the same time and at the same flow. Readings taken minutes apart may reflect a different compressor state or production event, so they cannot be subtracted honestly.
- Synchronise clocks. Set all loggers to one time reference before installation and confirm it at removal.
- Pick a suitable range. The transducer range must cover the expected pressure while still resolving differences of a few tenths of a bar. A 0–16 bar sensor is usually more useful than a 0–40 bar sensor on a 7 bar system.
- Do not mix gauge and absolute. State the pressure reference for each instrument and reconcile before comparing.
- Match logging speed to the problem. A one-minute average hides a two-second dip that stops a machine. Fast logging (one sample per second or quicker) is needed for dynamic complaints, while slower logging over several days suits load patterns.
- Record calibration and accuracy. Note the instrument accuracy and calibration evidence, and check all sensors against each other at a common point, or at zero flow, before the campaign.
- Log the context. Record production events, shift patterns, compressor start/stop, dryer purge cycles and any manual interventions in a site log.
A high-resolution trace will also show harmless pulsation, for example near a reciprocating compressor. Do not mistake ripple for a service failure. Judge every event against the process requirement and the method used to measure it.
How long should a pressure profile run?
Long enough to capture the events that matter. A single shift rarely shows the full picture. A typical campaign covers at least one full production week, including start-up, peak production, breaks, shift changes, cleaning cycles and the weekend or low-load period.
Low-load periods are valuable. If header pressure stays high and compressors keep loading when production is stopped, the remaining demand is mostly leakage and open blow-offs. Profiling and air demand profiling are best run together, because pressure alone cannot tell you how much air is flowing.
Reading the profile: a worked example
Suppose a plant logs these simultaneous readings during the worst cycling event of a filling line:
| Point | Pressure (bar g) | Pressure (psig) | Segment loss (bar) |
|---|---|---|---|
| Compressor header | 7.5 | 109 | – |
| Treatment outlet | 7.1 | 103 | 0.4 |
| Remote branch | 6.8 | 99 | 0.3 |
| Machine inlet | 6.2 | 90 | 0.6 |
The verified requirement for that event is 6.5 bar(g) (about 94 psig) at the machine inlet, so the machine is 0.3 bar short. The common reaction would be to raise the compressor to 7.8 bar. The profile says otherwise:
- The largest single loss, 0.6 bar, is in the last segment between the branch and the machine. That points to a small drop line, a restrictive coupling, a long hose or a regulator that droops under flow.
- The 0.4 bar across treatment is high for a clean, correctly sized dryer and filter set. Check filter differential pressure and element condition.
- Fixing the final segment alone could restore the machine to about 6.8 bar(g) without any change at the compressor.
Once the restrictions are corrected, the generated pressure may even be lowered, with roughly 7% less compressor power for each bar removed. That reduction is only accepted after it has been tested, as described below.
Common causes of pressure problems that profiling reveals
| Symptom in the profile | Likely cause | What to check next |
|---|---|---|
| Steady large drop across treatment | Loaded filters, undersized dryer, partly closed valve | Filter differential gauges, element age, dryer rating at site conditions |
| Pressure falls with distance in a smooth slope | Undersized or long header | Pipe diameter, length, flow velocity, opportunity to loop the ring |
| Short sharp dips at one machine only | Large intermittent user, small drop line, no local storage | Drop size, coupling size, local receiver near the user |
| Header swings widely every few minutes | Wide load/unload band or poor sequencing | Compressor control settings, sequencer logic, receiver volume |
| Plant-wide dip when a second compressor starts | Start-up delay with too little storage | Start trigger pressure, storage, VSD trim machine |
| High pressure held overnight with compressors still loading | Leakage and open blow-offs | Leak detection and a leak repair register |
From findings to a safe pressure change
A machine that runs once at a lower pressure has not proved it can run its full duty at that pressure. Any change to generated pressure or to a regulator setting should be treated as a controlled trial:
- Fix the restrictions identified in the profile first, then re-log the same points.
- Agree acceptance criteria with the process or equipment owner: cycle time, product quality checks, alarms and the worst operating event.
- Lower generated pressure in small steps, for example 0.2 bar at a time, while logging at the critical inlets.
- Hold each step through the relevant production states, including start-up and peak demand.
- Record the accepted setting, update the compressor and sequencer settings and keep the before and after profiles as evidence.
Keep in mind that compressor controls, demand, leakage and production volume all change over time. An improvement claimed from a pressure change should be compared at similar production and demand, not simply against last month’s power bill. Our page on audit reporting and verification covers how results are confirmed.
How Reddy Compressors helps
Our engineers carry out pressure profiling as part of compressed-air audits for plants across Telangana and Andhra Pradesh, working from our office at Tarnaka, Secunderabad. We are an independent multi-brand specialist, so we look at the whole system, whatever make of compressor, dryer or sequencer is installed: ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic and others.
- We plan the measurement points with your maintenance team and mark them on your piping diagram.
- We install synchronised pressure loggers, usually alongside power and flow logging so pressure, demand and energy can be read together.
- We interpret the profile segment by segment and rank the fixes: restrictions, treatment losses, control bands, storage and leaks.
- We can carry out the follow-up work: compressor control and sequencing adjustment, filter and dryer service, leak repair and service under an AMC.
- Where the profile shows the plant genuinely lacks capacity, we can supply new or used compressors, or a rental compressor while a permanent solution is decided.
Call +91 99590 60718 or +91 92468 88812, or email reddycompressors@gmail.com to plan a profiling campaign.
What to send us
- A piping layout or sketch showing compressors, dryers, receivers, headers and the main users.
- The make, model and rated pressure of each compressor, and how they are controlled or sequenced.
- The pressure complaint: which machine, when it happens, how long it lasts and what fails.
- The current compressor setpoints and any known regulator settings at critical machines.
- Your shift and production pattern, including weekends and shutdowns.
- Photos of the compressor room and of the problem machine’s air connection.
Frequently asked questions
What is the difference between pressure profiling and a pressure-drop test?
A pressure-drop test usually measures the loss across one component or segment, such as a filter or a pipe run, at a known flow. Pressure profiling logs many points at the same time over days of real production, so it shows how losses, compressor control and demand interact. The drop test confirms a suspected restriction; the profile tells you where to look and when the problem actually occurs.
Why is my machine short of air when the compressor gauge shows enough pressure?
The compressor gauge only shows generated pressure. Between that gauge and your machine sit dryers, filters, headers, drop lines, couplings, hoses and regulators, each taking a share of the pressure. During peak cycling these losses rise sharply. A profile logged at the header and at the machine inlet at the same moment shows exactly how much is lost and in which segment.
Should I just increase the compressor pressure to fix low pressure at the far end of the plant?
Usually not as a first step. Raising generated pressure costs about 7% more compressor power for each extra bar and increases leakage everywhere in the plant. If the shortfall comes from a restriction or a short dip at one machine, a higher setpoint treats the symptom at a permanent energy cost. Profile first, fix the restriction or add local storage, then decide.
How long does a compressed-air pressure profile take?
Installing loggers usually takes a few hours, depending on the number of points and access. The logging itself should cover the events that matter, typically at least a full production week including start-up, peaks, breaks and a low-load period. Short dips need fast logging, so the sample rate is chosen to suit the complaint before the campaign starts.
What pressure drop is acceptable in a compressed-air system?
There is no single correct figure for every plant, but a well-designed system keeps the total loss from compressor discharge to the point of use small, often well under one bar including treatment. More important than any rule of thumb is whether each critical user receives its verified requirement during its worst event, and whether any segment’s loss can be cut economically.
Can pressure profiling help reduce my electricity bill?
Yes, indirectly. Profiling identifies restrictions and control problems that force a higher generated pressure. Once they are fixed and a lower setpoint has been tested against production, the plant saves roughly 7% of compressor power for each bar removed and also loses less air through leaks. Savings should be verified by logging at comparable production, not estimated in advance.
Related pages
Calculators and worked examples
These tools give indicative figures for screening, comparison and for preparing an enquiry. They run in your browser and send nothing. No prices or tariffs are assumed: enter your own to see costs. Efficiencies and other figures shown are example values: replace them with your own. Results are not a performance guarantee or a design certificate; final selection is confirmed by a service engineer against the machine data sheet and the site.
Section losses at the worst moment of a pressure dip
Enter the pressures read at the same moment at the four section boundaries during a low-pressure event. The tool splits the loss into treatment, distribution and point-of-use sections and points to the part of the system to test first.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Compressor-room header (bar g): 6.9
- After dryer and filters (bar g): 6.8
- Main header near the affected area (bar g): 6.7
- Machine inlet, after its hose and coupling (bar g): 5.2
- Minimum pressure the machine needs at that point (bar g): 5.8
- Compressor state when the dip started: At least one compressor unloaded, off or below full speed
Result
- Treatment loss: 0.1 bar
- Distribution loss: 0.1 bar
- Point-of-use loss: 1.5 bar
- Total, compressor room to machine inlet: 1.7 bar
- Machine inlet against its minimum: -0.6 bar (below the minimum)
- Largest section loss: Point of use (hose, coupling, regulator, drop) 88% of the total
- Where to look first: Local path: the area header is above the machine’s minimum, so the shortfall is created between the header and the machine. Check hose, coupling, regulator and drop (gauge before and after them during a cycle) before touching supply.
Method. Section loss = upstream pressure − downstream pressure, all in bar(g) at the same timestamp: treatment = compressor-room header − after dryer/filters; distribution = after dryer/filters − area header; point of use = area header − machine inlet (hose, coupling, regulator, drop). If the area header is at or above the machine minimum while the inlet is below it, the shortfall is created locally. If the compressor-room header is above the minimum but the area header is below it, the shortfall is created in treatment or distribution. Only if the compressor-room header is itself below the minimum does the compressor state at the start of the dip separate capacity (all loaded), control response or storage (a machine unloaded, off or slow) and availability (a machine tripped or isolated). A negative section loss means the two sensors disagree: compare them on a common point.
What to take from it. Raising the compressor set-point costs energy everywhere. It is only the fix when the loss is in supply, not in one machine’s hose and regulator.
Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 7 November 2026. How our engineering content is reviewed.
Pressure budget and the cost of excess pressure
Add up the pressure that is lost between the compressor and the point of use, and see what a lower set-point would be worth.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Pressure needed at the point of use (bar g): 6
- Dryer and filter loss (bar): 0.5
- Piping loss (bar): 0.3
- Hose, fittings and regulator loss (bar): 0.3
- Control band and safety margin (bar): 0.3
- Current compressor set-point (bar g): 8
- Compressor input power (kW): 75
- Saving per bar reduced (%): 7
- Running hours per year: 6000
Result
- Total pressure losses: 1.1 bar
- Control band and safety margin: 0.3 bar
- Compressor pressure needed: 7.4 bar g (point of use + losses + band and margin)
- Possible reduction from current set-point: 0.6 bar
- Indicative energy saving: 18,900 kWh per year
- Indicative cost saving: Enter your electricity tariff (cost per kWh) above
Method. Required compressor pressure = point-of-use pressure + sum of losses. Savings = power × (reduction in bar) × saving per bar. A saving of roughly 6–8% of compressor power per bar of pressure is commonly quoted; it is indicative and varies with machine type and control, so edit it to suit.
What to take from it. The saving is real only if the farthest and most demanding point still works at the lower set-point. Prove it before you change the setting.