System pressure optimisation for compressed air

Why is my compressor set higher than it needs to be?

Few plants set their pressure by calculation. More often the setting has crept up over the years: a machine at the far end of the line complained, a filter blocked, a dryer was undersized, a new line was added on a long branch, and each time the answer was to turn the compressor up. The result is a whole plant running at, say, 8 bar to serve one user that needs 6 bar at its inlet but loses 2 bar on the way.

Typical reasons for excess pressure include:

• High pressure drop across dryers and filters, especially with clogged elements.
• Undersized or long distribution pipework and restrictive quick-couplings.
• One or two users that need higher pressure than the rest.
• Wide or overlapping control bands across several compressors.
• Pressure dips during peaks caused by inadequate storage, “fixed” by raising the setpoint.
• No pressure gauges or logging at the point of use, so nobody knows what pressure really arrives.

What higher pressure really costs

The cost of excess pressure has two parts.

More power at the compressor

Compressing to a higher pressure takes more work. A widely used rule of thumb for oil-injected screw compressors is about 7% more power for each additional bar. Higher pressure also slightly reduces the delivered flow of many positive-displacement machines, so more running time is needed for the same air.

Artificial demand across the plant

Every unregulated user consumes more air when pressure is higher. Leaks, open blow-offs, unregulated nozzles, worn cylinder seals and air motors without regulators all pass more air at 8 bar than at 6.5 bar. This extra consumption is called artificial demand. It means the compressor not only works harder for each unit of air but also has to make more units. In plants with significant leakage, artificial demand can be as important as the direct power effect.

Build a pressure budget from the user back to the compressor

The right generation pressure is found by working backwards from the process, not forwards from the compressor’s rating.

Adding these gives the minimum generation pressure. Comparing it with the actual setting shows how much pressure is being wasted, and the table shows where. The pressure budget builder and the pressure budget guide walk through the method.

Find the losses before lowering the setpoint

Turning the compressor down without fixing the losses simply moves the problem: the far-end user starves and the setting goes back up within a week. Instead, measure pressure at several points under real demand, ideally with logging gauges over a production period.

1. Log discharge pressure at each compressor and at the compressor house outlet.
2. Log pressure after dryers and filters to see treatment losses.
3. Log pressure at the main headers in each production area.
4. Log pressure at the inlet of the most demanding machines while they run.
5. Compare the readings during peak demand, normal running and low demand.

A loss that is small at low flow but large at peak indicates an undersized section. A loss across a filter that grows over weeks indicates a loading element. See pressure profiling and pressure-drop audits.

Common fixes that allow lower pressure

Should one high-pressure user set the pressure for the whole plant?

Usually not. If one machine, for example a press, a test rig or a specific pneumatic tool, needs 8 bar while everything else is satisfied by 6 bar, raising the whole system to serve it means paying for the higher pressure on every unit of air. Options to consider are:

• A small booster compressor at that machine, fed from the main system.
• A dedicated compressor for the high-pressure user.
• Local storage at the user if its demand is short and intermittent.
• Checking whether the user truly needs that pressure, or whether a loss near it is the real cause.

The choice depends on flow, duty cycle and criticality. Where high-pressure demand is genuinely large, a separate system is often better than a booster.

Reducing pressure in controlled steps

Once the losses are corrected, pressure reduction should be done carefully, because production and quality must not suffer.

1. Agree the minimum acceptable pressure at each critical user with production and maintenance.
2. Reduce the setpoint by a small step, often around 0.2–0.3 bar at a time.
3. Run for a full production cycle, including peaks, and log pressures at critical users.
4. Watch for slower cycle times, rejects, alarms or operator complaints.
5. Repeat until the agreed minimum plus margin is reached.
6. Record the final settings and lock them so they are not raised without investigation.

Check the compressor manufacturer’s minimum operating pressure, because some machines need a minimum pressure for oil circulation and separator performance. A minimum pressure valve normally protects this inside the package. Re-check settings before the hottest months, because summer conditions in Telangana and Andhra Pradesh can change dryer performance and demand.

Controls and storage support stable lower pressure

A lower setpoint only works if the pressure is stable. Wide control bands and slow response force a high setting to keep the lowest point acceptable. Narrowing bands is possible when:

• Machines are coordinated by a sequencer, so they share one band rather than each having its own.
• A variable speed trim machine holds pressure within a narrow range.
• Storage is adequate and correctly placed to absorb peaks.

Pressure/flow controllers downstream of storage can hold plant pressure steady while the receiver absorbs fluctuations. See pressure management and point of use, sequencers and storage for energy optimisation.

How Reddy Compressors helps

Reddy Compressors is an independent multi-brand specialist based at Tarnaka, Secunderabad, selling, renting and servicing ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic, Sullair, Doosan, Kirloskar, Gardner Denver and many other makes. We are not an authorised dealer of any brand. We have tie-ups with all major and reputed brands.

• Pressure profiling and pressure-drop surveys under real production demand.
• Pressure budget for your critical users and a ranked list of losses.
• Service of dryers, filters, inlet and minimum pressure valves, and control settings by our team of over 20 service engineers and technicians, across Telangana and Andhra Pradesh.
• Supply of boosters, dedicated high-pressure compressors, receivers, dryers and sequencers across India.
• Rental compressors from our own fleet to cover a changeover or trial.
• Follow-up logging to confirm the new setting holds and the energy result.

What to send us

• Current load and unload pressure settings on each compressor.
• Pressure required by your most demanding machines, with their make and model.
• Layout of the compressor house and main pipework, even as a sketch.
• Dryer and filter types and sizes.
• Known problem areas: low pressure at specific machines, dips at shift start.
• Compressor make, model and nameplate photos.

Frequently asked questions

What pressure should my air compressor be set at?

Set it at the lowest pressure that still delivers the verified requirement at your most demanding user, after real losses through treatment, piping and hoses, plus a small control margin. Many general industrial tools need around 6 bar (87 psig) at their inlet, but your figure must come from the equipment and from measurement. Fix avoidable losses first, then reduce the setting in small steps.

Does lowering compressor pressure save energy?

Yes, when it is done correctly. As a typical rule, each bar less discharge pressure on an oil-injected screw compressor needs about 7% less power, and leaks and unregulated users consume less air at lower pressure. The saving is lost if the reduction starves a critical user and the setting is raised again, so losses must be corrected first and the change verified.

Why is pressure low at the end of my air line?

Usually because of pressure drop on the way: undersized or long pipework, restrictive couplings and hoses, clogged filters, dryer drop at peak flow, or a large user drawing a surge nearby. Leaks also increase flow and therefore drop. Measure pressure at several points under load to find where it is lost, rather than raising the compressor setting.

What is artificial demand in compressed air?

Artificial demand is the extra air consumed by unregulated users, leaks and open blow-offs simply because system pressure is higher than needed. An opening passes more air at higher pressure, so raising the setpoint increases consumption across the plant. Reducing system pressure, and regulating users to their real needs, removes this extra demand as well as lowering compressor power.

Should I use a booster for one high-pressure machine?

Often, yes. If one machine needs higher pressure than the rest of the plant, a booster or dedicated compressor at that machine avoids running the entire system at the higher pressure. The choice depends on the user’s flow, duty cycle and criticality. First confirm that the machine genuinely needs the higher pressure and that a local loss is not the real cause.

How much pressure drop is acceptable across a compressed air system?

Good practice aims to keep total pressure drop from compressor discharge to the point of use small, often quoted as within about 10% of discharge pressure, and lower where possible. Individual items such as filters and dryers should be checked against their manufacturer’s stated drop at your flow. A survey under real peak demand shows whether your system meets this.

Related pages

• Compressed-air energy optimisation hub
• Pressure optimisation and artificial demand
• Pressure profiling
• Pressure budget builder
• Distribution energy loss reduction
• Specific power