Measured pressure optimisation project records

Why a lower setpoint is not proof on its own

Reducing generation pressure is one of the most effective measures in a compressed-air system. As a typical figure, each extra bar of discharge pressure costs about 7% more compressor power for the same delivered air, and leaks and unregulated users consume more air at higher pressure. That is why so many audits recommend it.

It is also one of the easiest measures to overstate. A plant that turns the setpoint down from 7.5 to 6.5 bar (about 109 to 94 psig) and sees lower kWh the next month may have saved energy, or it may have had a quieter production month, a compressor offline for service or a cooler spell of weather. Worse, a reduction that looked fine on a weekday afternoon may starve a press, a packaging line or an air-operated valve during a short peak, and the operators then quietly raise the pressure again.

A sound project record answers two separate questions. Did every critical user still receive the pressure it needs under representative demand? And what measurably changed at the compressor station as a result?

The pressure hierarchy: where to measure

Pressure falls between the compressor and the point of use, and it falls more at high flow. A record that quotes one pressure without saying where it was measured cannot be compared with anything. We record at least these points, with sensor positions marked on a sketch:

All sensors should use the same unit and reference (gauge or absolute), have a known accuracy, and log at an interval short enough to capture fast events. A one-minute average can hide a five-second dip that stops a machine.

Defining the critical end-use envelope

Before any change, agree with production and maintenance which users set the minimum pressure, and what that minimum really is. The answer is often lower than people assume, but it must be confirmed rather than guessed.

• List the users with the highest pressure need: presses, clamps, blow-off nozzles, air-operated valves, packaging machines, pneumatic conveying, test benches.
• For each, record the manufacturer’s minimum working pressure at the machine inlet and any quality or safety interlock tied to low pressure.
• Check whether a single high-pressure user is forcing the whole plant up; a dedicated booster or local receiver may be the better answer.
• Record known peak events: shift starts, batch blowdowns, cleaning cycles, simultaneous cylinder strokes.
• Agree the alarm or acceptance limit at each critical point, and who has authority to restore the old setting if a problem appears.

This envelope becomes the acceptance test. A project succeeds only if the critical points stay inside it throughout the representative period.

Running the before-and-after comparison

1. Log the as-found condition: pressure at all points, compressor states, station kW and, where possible, delivered flow, across at least one full representative production cycle.
2. Fix obvious losses first, or record that they were left: blocked filters, undersized hoses, open drains and leaks all distort the pressure profile.
3. Make the change in documented steps: new setpoints, narrower pressure bands, sequencing adjustments, regulators at points of use. Record date, time, who made each change and the previous values.
4. Watch the critical points closely after each step, especially at known peak events.
5. Log the as-left condition for a period comparable to the baseline in production, shift pattern and compressor availability.
6. Compare the two periods using the same sensors, boundary and intervals, and record every exception: alarms, operator complaints, interlock trips, temporary reversals.

Our pressure trend diagnostic workbook and pressure budget builder help structure this work, and the before-and-after comparison method page covers how to choose matched periods.

How the compressors and controls respond

Lowering pressure changes how the station behaves, and the record should show it. Typical effects include:

• Fixed-speed load/unload machines may cycle more often if the pressure band is narrowed too far, and unloaded running still draws a significant share of full-load power.
• Variable-speed machines reduce speed, but only within their usable turndown; below it they stop or unload.
• Sequencers or master controllers may need their bands reset, otherwise machines fight each other and the expected saving disappears.
• Receiver storage becomes more valuable, because a smaller margin above the minimum leaves less time to bring another compressor online.
• Desiccant and refrigerated dryers see a change in inlet conditions, and dryer performance should be checked as part of the record.

We note these responses because they explain why two plants making the same pressure change can see very different energy results.

Separating the energy result from everything else

An energy statement needs a defined meter boundary (compressor packages only, or including dryers, fans and ventilation), matched or normalised periods, and a clear list of other changes. Common confounders include production volume, product mix, new or removed air users, leak repairs, compressor maintenance, ambient temperature and shift changes.

Where the effects cannot be separated, report them together, for example “pressure reduction combined with leak repairs”, rather than attributing the whole change to one measure. Where only a calculation is available, call it an estimate, state its basis (the measured flow and the measured specific power in kW per m³/min, for instance) and keep it apart from measured values. A rule of thumb such as 7% per bar is useful for screening, not as proof of a result.

Exceptions, reversals and honest conclusions

A pressure project that had to be partly reversed is still worth recording. It tells the plant which user really sets the minimum, and it often points to a better fix: a larger branch pipe, a local receiver, a cleaner filter or a separate high-pressure supply. The record should list every low-pressure event, what caused it, and what was done.

Good conclusions are specific and bounded. For example: “After the change, all critical points stayed above their agreed minimum during the logged period, including two shift starts and one batch cleaning cycle. Station kW fell over matched production hours; the change exceeds the stated measurement uncertainty.” Unacceptable conclusions include a universal percentage saving, a claim that the new pressure suits all future production, or any figure the plant has not reviewed.

Indian plant conditions worth recording

Conditions in Telangana, Andhra Pradesh and much of India affect pressure projects. Summer ambient temperatures of 40–45 °C in compressor rooms reduce cooling margin and can push oil-injected screw discharge temperatures above their normal range of about 75–95 °C. Dust loads intake and cooler fouling. Unstable supply voltage can trip machines and cause pressure dips that have nothing to do with the setpoint. Recording ambient temperature and power events alongside the pressure trace prevents these from being misread as failures of the optimisation.

How Reddy Compressors helps

From our office at Tarnaka, Secunderabad, our service teams cover all of Telangana and Andhra Pradesh, and we support projects elsewhere in India where feasible. As an independent multi-brand specialist working on ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic and other makes, we can review a mixed station as one system.

For a pressure project we can map the pressure hierarchy, log pressure and power, check compressor condition and control settings, inspect treatment pressure drop, identify the users that set the minimum, and recommend changes such as reset bands, regulators, storage or a dedicated supply. Where the work needs a temporary machine, we can supply one from our own rental fleet. We follow the ISO 11011 assessment method for wider audits but do not issue conformity certificates, and any results we publish are anonymised and approved by the plant.

What to send us

• Current setpoints and pressure bands on every compressor.
• Compressor makes, models and nameplate photographs.
• A simple layout showing receivers, dryers, filters and main branches.
• The users you believe need the highest pressure, with their stated minimums.
• Any existing pressure, flow or energy logs.
• Known problem times: shift starts, batch events or past low-pressure trips.

Frequently asked questions

How much energy does reducing compressed air pressure save?

As a typical screening figure, each bar of pressure reduction saves about 7% of compressor power for the same delivered air, and leaks and unregulated users also consume less. The actual result depends on how the compressors and controls respond, what else changed and whether all users still get enough pressure. The only reliable figure for a specific plant is matched before-and-after station kW or kWh within a defined boundary.

How low can I set my air compressor pressure?

Only as low as the most demanding critical user allows, plus the pressure lost through dryers, filters, pipes, hoses and regulators at peak flow. Identify that user, confirm its minimum at the machine inlet, measure the losses upstream and leave a margin for peaks. Often one high-pressure user is holding the whole plant up, and a local booster or receiver is a better answer than a high header pressure.

Where should pressure be measured for an optimisation project?

At several points: compressor outlet, after the receiver, after treatment, on the main header, at key branches and at the critical points of use, downstream of the regulator and hose. Use the same units and reference at every sensor and a logging interval short enough to catch brief dips. A single controller reading cannot show what the users actually receive.

Why did our pressure reduction cause machine stoppages?

Usually because a peak event, a pressure loss or a particular user was not captured in the baseline. Common causes are blocked filters, undersized branch pipes or hoses, a too-narrow compressor band, slow start-up of a standby machine or insufficient storage. Logging fast pressure data at the affected user during the event normally shows which one, and the fix is often local rather than a return to the old setpoint.

Can a lower kWh bill prove the pressure change worked?

Not by itself. Monthly kWh also moves with production, shift pattern, product mix, compressor maintenance, leaks and weather. To attribute a change to pressure, compare matched or normalised periods within a defined meter boundary and list every other change. If other measures happened at the same time, report the combined effect honestly rather than crediting one action with the full result.

Do we need a sequencer to benefit from lower pressure?

Not always, but on a multi-compressor station the controls often decide whether the saving appears. Overlapping pressure bands can leave several machines running part-loaded or unloaded, and narrowing bands too far can increase cycling. Whether you use a sequencer, a master controller or carefully set local bands, record the settings before and after so the station response can be explained.

Related pages

• Compressed air project evidence centre
• Pressure profiling
• System pressure optimisation
• Pressure budget builder
• Pressure trend diagnostic workbook
• Measured sequencing optimisation project records