It’s possible to modify a double action airbrush to leave the air always on.
People who don’t want to turn the air on or off
People with fingers that easily tire – There’s usually a reason for fingers that get tired easily, like surgery or a medical condition.
Just about everyone
Most people will never need to worry about doing this modification. But what’s the fun of keeping strange and mostly useless knowledge to myself?!
Anyone with compressed air cylinders, unless they’ve got another way to turn off the airflow.
Let’s Do It
This is a really easy modification to both do and undo, but do consult your parts guide for terminology. We’ll be working on the air valve.
Notice the trigger doesn’t spring up and down anymore, removing the air valve and spring basically defeated the schrader valve, so your air will always be on until you replace these parts.
I put the set screw back in for aesthetics and just in case a big chunk of something flies through your airline, even though that almost never happens.