I built something a few months ago and didn't say anything about it until I had a chance to try it out for a while. I had to drag an answer out of Ninja to the simple question of "what size particulate in the air will cause significant tank regulator failure?" After being reported twice to the pbnation moderators, I finally got an answer. Ninja made excuses about how unreliable or "dangerous" an inline filter was. They claimed that you couldn't build a filter for less than $60 and then the liability cost would make the price ridiculous. Well situations arose and life got in the way of various projects I had in mind. Finally I got around to building this simple little device. I built the filter because about a year ago I went to a large scenario game. The organizers brought in a rented air system. I had 4 tanks at the time and 3 of the 4 tank regulators failed within minutes of being filled the first time on the rented air system. That was one huge coincidence!!! All 4 tanks had GA Myth 2 regulators and had been purchased new about 3-6 months previously and had never given me any trouble. The fourth regulator for whatever reason worked fine. I couldn't prove that the air fill was the problem since I had no way to trap debris from going into regulators and the guys running the air fill station swore they kept there equipment clean. Ummm yeah! Right! After the scenario was over I sent the 3 failed regs off to Guerilla Air for service. They had to replace the regulator seat in all 3 of them because they had stuff embedded in them from the air source. It has been almost a year since getting the regs serviced and they have worked perfectly ever since. I finally got around to building an inline filter after looking online for anything like it that wasn't going to be expensive. My solution is simple and inexpensive. I spent less than $30 for everything and it works well. I have trapped various bits of stuff in the filter while at my paintball field.
1. Male and female quick disconnect fittings. Take them off an old remote coil or buy them new somewhere. They are readily available for less than $15 for both fittings.
2. 1/8" NPT threaded pipe fitting with internal threads. I used a steel one, but brass would work too. You can buy them at any hardware store for a couple dollars.
3. Stainless steel filter screen. I scrounged mine out of an old car part. You can buy filter screen at any hardware or automotive store. Make sure it's stainless so it doesn't rust! DON'T USE PLASTIC SCREEN!!! I have found appropriate filter screen in faucet parts, various car parts and air compressor parts. Look around, you will find what you need.
4. Teflon tape.
What to do:
1. Cut the stainless steel screen into 2 circles that fit snugly inside the pipe fitting. Make sure to NOT leave any loose strands of stainless wire that might get into the regulator. I took the 2 circles of screen and placed them 45 degrees off from each other so that the screen holes didn't line up with each other which effectively makes it harder for stuff to pass thru the filter.
2. Put teflon thread tape on the threads of of one quick disconnect fitting and thread it into the pipe fitting until it is tight. If your pipe fitting is too long for the other quick disconnect fitting to thread in far enough to touch the other fitting then you may need an o-ring that fits snugly inside the pipe fitting. The idea is to trap the screen between the inside ends of quick disconnect fittings. An o-ring will probably be enough to make up the difference so that the screen can't move. My pipe fitting was just about perfect with both fittings threaded in all the way to hold the screen between them.
3. Put the screen inside the pipe fitting so that the 2 circles are pressed against the already installed quick disconnect fitting. Make sure the 2 screen pieces are NOT lined up with each other.
4. Put thread tape on the other quick disconnect fitting and thread it down tight inside the pipe fitting. Use an allen key to push against the screen to confirm it can't move.
5. Hook it up to a fill whip and open the valve to blow out any debris that might be inside that you missed.
That's it! Keep it in your pocket and attach it to your tank fill nipple and to the fill whip when you need to fill your tank. Just take it back off when done. My filter had trapped various bits of stuff that would have otherwise gotten into my tanks in the past couple of months. It has worked perfectly and given me no trouble at all. It takes an extra second or so to attach it between the fill whip and tank fill nipple. Cleaning out the filter is super easy. Just knock the input side on a table and any loose bits will fall out. You could also blow air into the output side which would blast out anything stuck in the screen. It doesn't catch everything that could get into your tank, but the goal was to stop junk that is large enough to cause reg leaking or failure. I have 3 Macdev guns and the inline regulators all have a filter screen. In all of those guns when I service the regulators I have found bits of stuff on the filter screen. I'm curious to see if they stay clean now. In my DP G4 the solenoid developed issues. When I took it apart I found a small piece of hard black "something" that was keeping it from working. Once I cleaned out all the ports inside the solenoid and relubed the spool, the solenoid worked perfectly. My guess is that the black thing got in the solenoid from dirty air.