For a 2 m wide optical sorter, start from the consumption the manufacturer gives at your real ejection rate, add a 20% margin, and choose a screw compressor that holds that flow at the required pressure. Depending on the material and the share of objects to eject, a machine of this width often needs a few m³/min: an S 220 PM (3.6 m³/min at 8 bar) is enough for a lightly loaded sort, and two machines become necessary beyond that.
Our page on the compressor for recycling and waste sorting covers the air needs of a whole site. Here we focus on a single sorter.
Why width is not enough
An optical sorter detects each object on the belt and ejects it with a short air jet from a row of nozzles. The width sets the number of nozzles, but not the number of jets. What uses air is the number of objects ejected per second and the length of each jet.
Two identical 2 m sorters can therefore use anything from one to two times the air:
- one sorts out a rare fraction, a few objects in a hundred;
- the other ejects one object in three, on a heavily loaded belt.
In practice, consumption roughly follows the quantity of objects ejected. If your material stream changes, consumption changes with it.
The calculation, step by step
Example: the manufacturer's data sheet gives 4.5 m³/min at 7 bar for your material and ejection rate.
- Sorter consumption: 4.5 m³/min at 7 bar at the machine inlet
- Pressure at the compressor: 7 bar + about 1 bar of losses (dryer, filters, network) = 8 bar
- 20% margin for stream variations and leaks: 4.5 × 1.2 = 5.4 m³/min
- Flow required: 5.4 m³/min at 8 bar
If the data sheet uses l/min, Nm³/h or cfm, the flow and pressure converter switches between units. Also check that the manufacturer's figure matches your own ejection rate, not a demonstration setting.
Which compressor for which case?
| Case | Demand at 8 bar, margin included | Possible choice |
|---|---|---|
| Rare fraction, data sheet at 2.5 m³/min | 3.0 m³/min | One S 220 PM, 3.6 m³/min at 8 bar |
| The example above, data sheet at 4.5 m³/min | 5.4 m³/min | One S 220 PM plus one S 150, 3.6 + 2.2 = 5.8 m³/min |
| Same sorter, air must never run short | 5.4 m³/min | Two S 220 PM, 7.2 m³/min, one alone keeps running at reduced output |
| Beyond that | S series up to 132 kW on request |
Every compressor in the S series runs at variable speed: output follows the ejection rate, which changes with the material stream. For a site with several sorters, balers and dust collectors, the balance is drawn up station by station; the guide what size compressor do I need explains the method.
A setting tip: eject the minority fraction
Where possible, set the sorter to blow out the smaller fraction and let the other pass. If the target material makes up 70% of the stream, ejecting the remaining 30% uses far less air than the reverse. Your manufacturer will tell you whether this mode is compatible with the purity you need.
Traps specific to optical sorters
- Pressure dropping at the wrong moment. A burst of ejections pulls down the pressure at the nozzle bar, and the jets lose accuracy. A buffer receiver as close as possible to the sorter absorbs these bursts. The air receiver size calculator gives a first volume for the compressor's own receiver.
- Fouled solenoid valves. Ejection valves are fast and fine. Water, oil or particles make them stick. Our screw compressors are oil-lubricated: plan a dryer and fine filters to meet the ISO 8573-1 class the manufacturer asks for.
- A network that is too long or too narrow. Pressure losses eat into the margin. See connecting a compressor to the air network.
- Dust. Install the compressor in a closed, ventilated room, with the air intake on the clean side. See the compressor room.
Send us your sorter's data sheet, the material sorted and the expected ejection rate with a quote request: we will size the compressor, dryer and receiver with you. You can also start with the configurator.
For your trade: Compressor for recycling and waste sorting.