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Wednesday, April 24, 2013

Zen and the Art of Airbrush Maintenance: Oh you, O-rings!

Iwata HP-BH. Excellent for the scale of our hobby,
though I sometimes wish for a bigger color cup.

I want to talk about o-rings. They are very important to the operation of airbrushes. Simply put, o-rings are there to make a seal. They block air and/or fluids from flowing between parts at a joint. Unlike the stainless steel parts of your airbrush, they do not hold up well when exposed to organic solvents and other cleaning agents. Being made out of rubber, under the wrong conditions they can corrode or maybe swell.

Luckily for me I haven't had any problems like these (yet). The problem I had recently was pretty simple, but figuring that out took a good deal Googling and reading. Basically, the trigger was sticking which meant air was continually flowing through the valve. There are a two most likely causes for this. One could be that the o-ring is swollen and squeezing the piston. That could prevent the control spring from returning the button to the off position.

In the image above, the control spring is inside that detached piece, which is the air valve set. Air flows through this when the piston, visible as a silver circle in that hole just below my index finger, compresses the pin at the top of the valve set. The piston o-ring is barely visible around the piston there.

Disassembled airbrush with the top of the piston visible through the trigger slot.
The other cause, the one that I had trouble with, is that the o-ring could need lubricant. If there is too much friction between the piston and the o-ring, it could cause the same problem as the situation I described above.

Here you can see the o-ring and the piston separately.
From what I have read, you have to be incredibly sparing in how much you apply. Using too much could result in getting oil all throughout the air passages. That could contaminate your work later on when you spray. I used a toothpick and a really tiny kind of Q-tip I buy from a local hobby shop. Apparently you also need to avoid some oils that can damage the rubber. Iwata has a specialty lubricant of their own, but as with most specialty goods I expected my local hardware store would sell a product in some ridiculous quantity I could never use up. Probably 90% cheaper than the brand name one too.

What I found was a huge tube of lithium grease. I wasn't sure that the recommended lubricant, Medea Superlube, was a lithium grease so I had to Google until I found the material safety data sheet (the MSDS). Be sure to look around for yourself if you want to use an off-brand as different companies use o-rings made of different materials.

This post is mostly about the o-ring that was giving me trouble, but there is another important o-ring in my model (probably in all of them, I'd think) and it is the one that creates a seal around the needle. I couldn't get a picture of it, but it is just behind the color cup. That one also needs to be lubricated as you don't want friction between it and the needle. I wasn't having any problems with that one, but I went ahead and greased it anyway while I was at it.

When I finished, I sprayed two shades of purple over the course of an afternoon and didn't have any more issues with the trigger. I'll post more about these sorts of topics, but it'll be most likely if I have a problem with some of my hardware. Let's hope that's not the case!