Unloader/inlet valve mounted
on top of compressor element (portable
Note that there is always a small hole in the air compressor unloader valve, so it will never close 100%. This is to make sure there will be enough oil flowing for lubrication and cooling.
Most unloaders are of the LOAD/UNLOAD type. Which means they are either completely open (compressor
loaded) or completely closed (compressor unloaded). In unloaded state, when the unloader is closed, the
unit will consume about 30% of it’s nominal power.
There is another type: CONTINUOUS or MODULATING. This way the compressor can work at any point between 0 and 100%. It is not often used in stationary compressors (it’s not the most economical way of regulation). But it is often seen in portable diesel engine driven compressors.
Example of inlet/unloader valve… This one is from a 15 year old rotary screw compressor (Atlas Copco GA37)
Inlet valve on old stationary rotary screw compressor.
Another example… this is the inlet valve of a brand new screw compressor (Atlas Copco GA30).
Brand new inlet valve, with small control valve and solenoid on the right.