A buffer receiver for an optical sorter is sized on the ejection bursts, not on average consumption. The formula is simple: volume (L) = air shortfall (l/min) × burst duration (min) × 1.013 / accepted pressure drop (bar). For a 10-second burst that exceeds the compressor by 2,400 l/min, with a 0.5 bar drop allowed, you get about 810 L, so a standard 900 or 1,000 L receiver.
The overall air demand of a sorting plant is covered on our page on the compressor for recycling and waste sorting. Here we deal with the receiver fitted at the foot of the sorter.
Why a receiver next to the sorter?
An optical sorter's air demand is not steady. When a cluster of target material arrives on the belt, the nozzles open in a burst and consumption can double for a few seconds. The compressor, even at variable speed, does not respond on that time scale, and the network between the two holds the air back. Pressure drops at the nozzle bar, the jets weaken, and objects end up in the wrong stream.
A receiver placed as close as possible to the sorter supplies that peak air immediately, then refills between bursts.
The calculation, step by step
Take a sorter that uses 3.0 m³/min on average, with bursts of 6.0 m³/min lasting 10 seconds. It is supplied by an S 220 PM, which delivers 3.6 m³/min at 8 bar. The sorter needs 7 bar and tolerates a 0.5 bar drop.
- Shortfall during the burst: 6,000 − 3,600 = 2,400 l/min
- Burst duration: 10 s, or 10/60 of a minute
- Free air the receiver must supply: 2,400 × 10 / 60 = 400 L
- Receiver volume: 400 × 1.013 / 0.5 = 810 L
- Standard receiver: 900 or 1,000 L
The parameter with the most weight is the accepted pressure drop. With a 1 bar drop allowed, the same calculation gives 405 L, so a 500 L receiver. With only 0.25 bar, you need over 1,600 L, so a 2,000 L receiver. Ask the sorter manufacturer for the minimum operating pressure, then keep the receiver charged above it.
Check the refill time
A receiver stores air; it does not make any. After the burst, the compressor's surplus refills it:
- Surplus in normal running: 3,600 − 3,000 = 600 l/min
- Air to put back into the receiver: 400 L
- Refill time: 400 / 600 = 0.67 min, or about 40 seconds
If bursts come more often than every 40 seconds, the receiver never fully refills and the pressure slowly sinks. A larger receiver does not solve that: you need more flow, for instance an S 150 backing up the S 220 PM.
And the compressor's receiver?
That is a second receiver, in the compressor room, with a different job: spacing out starts and steadying the control. Our air receiver size calculator uses the usual formula V = 0.25 × Q × p₀ / (f × Δp). For an S 220 PM at 3,600 l/min, at most 60 cycles per hour and a 1 bar pressure band, it gives about 910 L, so a 1,000 L receiver.
Where and how to fit the buffer receiver
- As close to the sorter as possible, after the dryer and filters, with a short, large-bore connection. A receiver at the end of a narrow pipe can neither empty nor refill quickly. See connecting a compressor to the air network.
- With an automatic drain. Even after a dryer, a receiver standing in a cold hall can collect water. An automatic condensate drain stops it reaching the solenoid valves.
- At the right working pressure. Choose an air receiver whose maximum pressure exceeds the compressor setting. 13 bar versions exist for networks set higher.
- Without leaks. A buffer receiver adds fittings. Check them regularly: see how to detect and repair leaks.
With two sorters on the same network, plan one buffer receiver per sorter: a burst on one must not pull down the pressure on the other.
Send us your sorter's data sheet and the minimum pressure it needs with a quote request: we will size the compressor and receivers with you. The configurator gives a first choice of compressor.
For your trade: Compressor for recycling and waste sorting.