In an oil-injected screw compressor, oil is injected into the screw element during compression. It comes out mixed with the air. So before the air leaves the machine, that oil has to be recovered: that is the job of the air/oil separator cartridge.
Its role: keep the oil in, let the air out
The cartridge sits inside the separator tank. It separates the lubricating oil from the compressed air:
- the oil stays inside the compressor and returns to the lubrication circuit to be reused;
- the compressed air passes through the minimum pressure valve, located above the separator, and is then sent to the air receiver (the air tank).
Without an effective separator, the oil would end up in your air network and the machine's oil level would drop with every operating hour.
What does the cartridge look like?
It is a perforated sheet-metal cylinder containing the separation media, with a wide gasketed flange that is clamped into the separator tank. Its size depends on the compressor's air flow: each model has its own part number. You will find it in our spare parts, with the compatible models.
Signs of a worn separator
The separator wears with operating hours. Watch for:
- abnormal oil consumption: the level drops faster than usual;
- oil in the network, at the drains or at the tool outlets;
- a pressure loss at the compressor outlet, or a motor that is straining: a sign of a clogged separator.
When should you replace it?
It is changed at the interval set by your machine's maintenance plan, usually during a service, together with the air filter, the oil filter and the oil. The usual intervals are detailed in our article When should you service a screw compressor?. Your machine's intervals are the ones in its manual.
The simplest option is to order the service kit for your model, which brings together the parts for the service.
Replacement: machine stopped and depressurised
The separator sits on the pressurised oil circuit. Before touching it, stop the compressor, lock out the power supply and fully release the pressure. An automatically regulated compressor can restart on its own as long as it is powered. If you prefer to hand the job over, our after-sales service takes care of it.
To see where the separator sits in the machine, read How does a screw compressor work?.