Compressed Air for Optical Sorting: Planning for Harvest and Crop Changes

Treat each harvest change as a compressed-air recommissioning point. The sorter may stay the same, but crop condition, throughput, rejection rate, operating hours and simultaneous plant demand can all alter its air profile.

A 2024 industrial food-sorting study describes a sorter that detects defects with RGB and NIR cameras, then rejects them with compressed-air solenoid ejectors. The ejector air supply decides whether each detected reject clears the product stream. Pressure, flow and purity at the sorter inlet shape both sorting performance and operating cost.

Anglian Compressors, a Branch of Atlas Copco Compressors, works with processing sites across the East of England. We specify the compressor, treatment equipment, storage and pipework as one system rather than treating the sorter as an isolated connection.

Start With the Worst Operating Week

Do not size the system from average shift consumption. Establish demand during the crop, throughput and rejection conditions that place the greatest load on the ejectors, then add the other compressed-air users that may operate simultaneously.

The difference between sorter configurations can be substantial. The Cimbria SEA.CX datasheet, for example, lists maximum consumption at 6 bar from 150 L/min for its half-chute model to 2,100 L/min for its seven-chute model, on the manufacturer’s stated reference basis. That is 9 to 126 m³/h before any allowance for other equipment, so confirm the reference conditions before adding it to other loads.

Record the Peak-Demand Profile

Record for each harvest campaign:

• Sorter make, model, number of chutes and manufacturer-stated inlet pressure
• Maximum and typical air consumption for each crop recipe
• Expected tonnes per hour and operating hours
• Other equipment sharing the compressed-air main
• Planned expansion or an additional sorting line
• Dryer purge air and other continuous system losses

Size the supply from the measured worst-case event plus any defined expansion, such as a planned additional sorting line. Validate that figure against logged site data and the sorter’s documentation. A fixed percentage margin cannot compensate for an unknown load profile.

Seasonal duty matters as much as peak flow in compressed air in agriculture. For vegetable and grain packers across the Fens and wider East Anglia, a system that is comfortable during short spring campaigns may run close to its limit during continuous autumn intake.

Hold Pressure at the Sorter Inlet

The sorter responds to dynamic pressure at its own inlet, and the compressor room gauge says little about that. Measure downstream of the dryer, filters, regulators, distribution pipework and final hose while the sorter is operating at peak demand.

Short ejector pulses can expose restrictions that remain invisible on an average pressure reading. Small-bore branches, contaminated filters, restrictive couplings and long hoses may leave the compressor maintaining its setpoint while pressure collapses at the machine. Our guide to pressure drop in compressed air systems explains how those losses accumulate.

Do not raise the compressor discharge pressure before finding the restriction. As a Branch of Atlas Copco Compressors, we work to the rule of thumb in our Atlas Copco guidance on compressed air management: reducing system pressure by 1 bar may save about 7% of electricity consumption. Project savings must come from site measurements.

A local air receiver can reduce disturbance from short pulses, but undersized pipework still needs correcting. HSE compressed-air guidance calls for suitable pressure indication, drainage and protective arrangements, with drain valves, safety valves and examination openings accessible.

Set Air Purity From Process Risk

Obtain the sorter’s permitted particle, moisture and oil limits in writing, then reconcile them with the site’s food-safety assessment and cleaning regime. State the requirement at the sorter inlet as an ISO 8573-1 class in particles:water:oil form, with the test point and operating condition named.

Class 0 has no fixed limit in the standard’s table. As our Atlas Copco guide to ISO 8573-1 air quality classes explains, the user or equipment manufacturer defines it, and it must be stricter than Class 1. Where ejector air contacts food, the site’s HACCP-based food-safety plan sets the class, test point and monitoring frequency, because UK food law does not prescribe one fixed ISO 8573 class.

Check the pressure dew point against the coldest pipework, nozzle or enclosure the air passes through. Autumn and winter intake tests that margin, since a dew point that suits a heated building can allow condensation in pipework running through unheated areas.

Air leaving the treatment package may pick up condensate, corrosion or debris before reaching a remote sorter. The specification should cover dryer performance, filtration, condensate drainage, distribution materials and point-of-use testing.

Crop changes can also alter the surrounding dust and moisture burden. Do not repurpose the sorter supply for routine blow-down in dusty areas. HSE food-industry guidance advises using a fully earthed vacuum-cleaning system and avoiding compressed air except for non-dusty cleaning activities because suspended combustible dust can create a fire or explosion hazard.

Recheck Demand When Ejectors Wear

A rising air requirement does not automatically mean the compressor is undersized. It may be a maintenance signal from the sorter.

In a manufacturer study, Bühler reported that worn ejectors consumed more than twice the air of new units. Refurbishment reduced air use by up to 60%. The company gives approximate wear lives of two billion cycles for small dry products and one billion for wet or frozen products.

Those figures come from Bühler’s own study, so treat them as a reason to trend air consumption over each campaign.

Record flow, point-of-use pressure and filter differential pressure at the start of each crop campaign. If consumption rises while throughput and rejection settings remain comparable, inspect the ejectors and valves before approving more compressor capacity.

Make Compliance Part of the Layout

Compressed air above 0.5 bar gauge is a relevant fluid under the Pressure Systems Safety Regulations 2000 (PSSR), so qualifying equipment needs a Written Scheme of Examination in place and its examination completed by a Competent Person before use (HSE PSSR overview). Adding a receiver beside the sorter, even a small one, can change what the scheme must cover, so have it reviewed before the receiver goes in.

Safe maintenance also needs designing in. HSE guidance under PUWER 1998 calls for electrical and pressure supplies to be isolated, valves locked where necessary and stored compressed air released before work begins. Access for isolation, drainage, filter changes and examination should be resolved during the compressor installation, before the line enters production.

Give the Engineer Enough Evidence to Specify the System

A useful quotation needs the sorter datasheet, crop schedule, peak throughput, operating hours, air-purity requirements, pipe route and details of every simultaneous air user. Include existing compressor, dryer, filtration and receiver information alongside any recent pressure or flow records.

Our team can check treatment and storage, review PSSR implications and produce equipment and pipework recommendations as part of a compressed air energy audit. Book a free energy audit and we will data-log your system, then show you where air is being lost, what it costs per year and the payback period for supported changes.

Send us the sorter documentation and your next harvest schedule through the form below. We can then assess the measured system against the campaign you are preparing to run.