Plasma Cutter

[MadReferee]

Regarding relative humidity, you are now beyond my area of expertise. I do know that RH is the measure of moisture in the air so it only makes sense to remove RH before sending the air to the plasma cutter.

[egon]

I was thinking more along the lines of a regenerating desicant dryer at about 400 PSI. Not the throw away cartidge type. [img]/forums/images/icons/grin.gif[/img]

Egon

[Pat]

Mad, The relative humidity is the fraction (expressed as a percentage) of how much water is in the air compared to how much water the air could hold at that temp and pressure. So, 50% RH is when the air has half as much water in it as it could have before dew or fog would start forming.

The toilet paper type (and all other particulate filters without a dessicant or some sort of refrigeration) in the long run do not change the RH much if any. Of course a really dry toilet paper filter element would take a little moisture out of the air until it got as wet as the air and then it would have no further effect on the RH.

I guess I'd have to corner a welding engineer to find out if RH matters much to a plasma cutter or if the major concern is water droplets. Water droplets can contain and carry contaminates. Water vapor doesn't.

Dessicant type filters are used when you need DRY air with little or no water vapor. I will be trying to find out if water vapor makes much difference before I would go to the complication of a dessicant or refrigeration type dryer.

Clearly, I need to get a particulate filter such as you recommended. That will stop particulate contamination, both liguids such as water and oil droplets as well as dirt, dust, rust , and so on. If the filter is after the tank then you need a fairly large sg ft of filter area so as to not overly restrict flow. Filter cartridges such as I used in marine diesel service are available to stop virtually all particles 1/2 micron or larger and I'm sure there are similar for air.

Even a HEPA filter for a vacuum cleaner would do just fine as far as filtering well with a very low flow restriction at delivery rates to be had with a typical shop type compressed air sytem. The tough part would be the housing that would safely handle the pressures and be easily opened and resealed. A DIY canister to hold a roll of toilet paper is nearly trivial, just some pipe, plumbing fittings, and a little ingenuity.

There used to be an aftermarket oili filter for cars that used a roll of toilet paper as the user serviced filter element. If I recall correctly, it was used in additioin to instead of in place of the stock filter arrangement and significantly extended the life of the OEM filter by acting as a prefilter to collect much of what would plug up thte OEM filter.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[MadReferee]

I believe, from reading various discussions on several welding boards, that water droplets as you call them, are the real culprit when plasma cutting. Most hobbiest and most professional shops that do only occassional plasma cutting use a MotorGuard or a similar product. Those shops that do a lot of plasma cutting use a stand-alone air dryer. They all also use some type of particulate filter.

Don't over think and over engineer a solution.

[Pat]

Mad, I was converging on the same concensus you support, I think. Non-condensing humidity isn't the BIG problem so I will probably build or buy a filter to protect against compressor oil, and water droplets and tr5y to not worry abot RH until or unless I observe a problem such as short consumables lifetimes.

Again thanks for your comments.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[MadReferee]

Here is something that I just came across and is reasonably priced (under $200) and will work for most applications where the run from the compressor to the plasma cutter is not all that long. By long I mean less than 100 ft as anything longer might induce more moisture which would require a MotorGuard at the cutter.

Filter setup

[Pat]

Mad, Thanks for the info. I have bookmarked their site and sent for their catalog.

I don't understand the length restriction you discuss. Once the air is filtered, unless the distribution plumbing is contaminated, where is contamination going to come from? If you have rusty or dirty pipes then the upstream filtration will not solve your problem anyway, no matter what the length of the distribution run if it is of any practical length.

If the air exiting the filter is hot and the distributiion plumbing is cool, then there is a possibililty of condensation in the pipe but this is true even for a short run. My shop has A/C and the pipes will be cooled so that is a distinct possibility for me. I have a new compressor to be mounted (bolted down) which isn't hooked up yet. It will in the 21x48 shed that runs along the side of the shop. I am using a portable compressor and rubber hoses right now. When I plumb for air I am thinking I will put a heat exchanger on the inside plumbing from the compressor to get the air cooled (encourage condensation) and put the filtration downstream of that.

In order to reduce the moisture accumulation in the tank as well as in the output to the shop, I will build a little adaptor with some gaskets to fit around the air intake to the compressor so that the input air can be supplied to the compressor from inside the shop where the air is often cooler and nearly always dryer I can put a good filter pad on the input air.

I also have a kit to install on the compressor to automatically drain condensation from the bottom of the tank. I have one on the portable compressor too and recommend them. Who remembers to drain the compressor tank daily or more often? NOT ME! The kit was, if memory serves, $16 and should be well worth it in helping to preserve the life of the tank.

Thanks again for the URL,

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[MadReferee]

</font><blockquote><font class="small">In reply to:</font><hr />
I don't understand the length restriction you discuss.
...
If the air exiting the filter is hot and the distributiion plumbing is cool, then there is a possibililty of condensation in the pipe but this is true even for a short run. My shop has A/C and the pipes will be cooled so that is a distinct possibility for me.

[/ QUOTE ]
I think you answered your own question. [img]/forums/images/icons/grin.gif[/img] [img]/forums/images/icons/grin.gif[/img]

Professional painters usually have water separators at the beginning and at the end of the line near the paint gun just so moisture induced while in the line can be removed.

[Pat]

Mad, I may live to regret it but I bought a filter assy with gauge and regulator with removable cartridge and ball valve, all sized for more flow than I have to have, ON SALE built by our Chinese cousins for a pittance, by comparison. $29.95 and shipping as a part of a larger order.
Filter-Regulator

As you can see if you look at it on the site above, there is a drain petcock on the bottom for accumulated water. If this doesn't do enough (I think it will) I can add something ro replace it. I haven't got a big investment.

I also bought a filter-regullator-oiler on 1/2 price sale ($23.) I will use that with my air tools instead of stopping what I am doing to drip oil into the air fittings every so often. Since I am a one man shop I can really only use one tool at a time so I don't have the highest volume requirements and expect these cheap Chinese devices to be fine for my needs.




[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[MadReferee]

I think you will find that the HF unit is not all that good. If you look at my setup in one of my first posts in this thread you wil see that I have one of these also, and I had to put a MotorGuard after it because it (the HF unit) doesn't do the job.

Remember, ANY moisture will cause the cutter tip to deteriorate within minutes causing a crappy cut among other things. That HF unit will not "cut it" so to speak. Tips should last 20-30 minutes of cutting time with no moisture. They will last a minute or two with moisture.

Do a little reseach on forums such as ShopFloorTalk, MillerMotorSports, or HobartWelders and you will see that the pros and hobbyists all agree that moisture is the big plasma cutter killer and that the most cost effective method for casual plasma cutting to eliminate the moisture is to use the MotorGuard. Going the cheap route is not always the best way. I learned the hard way and it looks like you will too.

Good luck with your projects.