The idea is that air bubbles are forced through the ferric chloride etchant and float up over the board being etched. The bubbles agitate the solution and give a faster and more even etch result, and when the darn thing works, it works well.
Around a year ago, I noticed that the bubbler wasn’t working as well as it used too and that bubbles were only appearing at one end of the bar and even these were very tiny and intermittent and since I’d not emptied and cleaned the tank for a couple of years, I suspected that it was just in need of a good service. The old ferric chloride was removed, neutralised and disposed off and the tank cleaned with caustic soda solution and rinsed several times. I filled the tank with cold fresh water and switched on the air pump… nothing except for a tiny little stream of bubbles at one end again.
On dismantling the tank I found the pump to be in good order so decided it must be the bubbler bar holes that were blocked.
Removing the bar is a simple though messy job and once out, I attempted to unblock the 12 or so holes using a pin. After fiddling around for half the morning, I reassembled the unit and hey presto it worked. I think the problem was caused during a long period of inactivity. The sludge from etching process seems to have settled in to the bar and blocked the holes.
Fast forward a couple of months and this morning, the bubbler bar is blocked again.
I of course don’t have a replacement bar and whilst I’ve been putting up with the slowly worsening bubbler performance, today I’d had enough; time to fix this for good.
The tank was drained, washed out and the bubbler bar assembly removed; it was indeed blocked with sludge again, but instead of attempting to poke a small pin through the holes and unblock them, I re-drilled out the holes using a 0.8mm bit making them slightly bigger than they were and on forcing water through the bubbler bar, all sorts of rubbish and debris started to spew from the holes.
The unit was re-assembled and again works perfectly even with the slightly larger holes. The hope is that as the holes are a little larger, they won’t block so quickly in the future.
So whilst that’s £8 saved on a replacement bubbler bar, heaven knows how much I've spent in latex gloves, kitchen role and time fixing the ruddy thing.