On the subject of plasma cutters...

An answer to a question I asked over in rec.crafts.metalworking got me curious as to just how dry the air feeding a plasma cutter really needs to
be. The suggestion of what was required sounded overkill in comparison to the successful setups I have seen around my location, but then I do live in a less humid area than some folks and so that might make a difference. Just how much cooling and drying of the input air is required, and at what stages in the compression cycle (i.e. pre/post compressing)? I'm sure this varies by geographic location, and would be much different if I lived in, say, Louisiana instead of Southern California, but is there some basic guideline that can be followed in terms of humidity percentages? Personal experience with particular real world setups would be most appreciated. Thanks!
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On Wed, 21 Jan 2004 03:16:04 GMT, The Hurdy Gurdy Man

I only have a simple trap in the air-line to my plasma cutter and have had zero problems to date. Mind you, I'm also lucky enough that I can choose to use my cutter only on days when the relative humidity is less than 45%.
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On Wed, 21 Jan 2004 03:16:04 GMT, The Hurdy Gurdy Man

To put things in terms that might be more familiar to you or your air system supplier, you want the air for a plasma torch to be as dry as the air you'd use for high quality spray painting.
As you noted, different climates will require different degrees of effort to reach that level of dryness. Here in not too humid North Georgia, I find a simple coalescing filter sufficient. But in the much more humid environment of my farm along the Ohio River, I need a refrigerator dryer too.
Precise relative humidy numbers aren't easily obtained because RH will vary (increase) as the air expands and changes temperature when released from the compressor. In other words, the RH of the input air could be 40%, and fall to less than 20% after being heated by the compressor, then jump to 100% as it expands and cools downstream of the tank regulator.
The latter is obviously undesirable, so you need some way to suck enough water out of the air before it expands, or at least before it reaches the plasma torch, so that you have a non-condensing humidity.
Gary
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My understanding is that it will work, but that the consumable parts will last longer with truly dry air.
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This is a post I made sometime ago on the topic of air systems the only change is my location, we moved from NY to VT.
{{{I spent some time researching my air system and I now have a set up I like. I was using 30 gal vertical craftsman single stage oil-less with a hose direct to the plasma cutter. I also had a water trap/filter on the cutter, it would fill up quickly. The compressor was about 2 yrs old when I got the plasma cutter, at the time it did the job but the run time just kept getting longer with more water in the air all the time (also the noise was incredible). What I have now is the following:
An Ingersall Rand 2 stage belt drive 5 hp. 60 gal vertical tank (the reduction in noise was huge, what a difference) this connects to " black iron pipe with 2 drops 1 at the unit and 1 at the plasmacam, it's about 30 ft of pipe properly pitched with drip legs, drain valves ect. At the plasma end I have a filter setup; it has a general filter/water separator then an oil filter and finally a desiccant style dryer. The dryer is filled with silica gel and it can be rejuvenated in the oven when it gets saturated. This hooks to the cutter by hose. I get better cuts (significantly better on non-ferrous) and use fewer tips. It's hard to say exactly how much longer things are lasting because I haven't had the table set up that long but it is noticeable. This system will also improve my painting and is better suited for a blast cabinet as well as being durable. The cost? $1200 for the compressor, $200 for the filters (got lucky at the surplus shop, saved about $200 over brand new) and I spent about $75 on valves and pipe. Basically $1500, not inexpensive but it will be cost effective in the long term.}}}}
Andy
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