Importance of water filter in air line

Most air tool manufacturers recommend having a water filter in the air line "as close to the tool as possible". E.g. Paslode specify within

10 feet, OTOH Bostich do not mention water filters at all in their FAQ (I could not download any manuals).

The question is how much water is damaging enough to justify trying to get an in-line filter close to a tool with all that it entails. Is the water filter really necessary for limited use as opposed to continuous use for a whole day?

I was trying to quantify this somewhat and thought the best example would be nailers (although not necessarily metal-related ). If one used a brad nailer for the occasional job that entails 200 or so fasteners at a time would inserting a water filter be justified even though it is a hassle, added expense and another potentially weak point in the line?

Is there difference in how the water vapor affects different types of air tools?

Is there a way of assessing how much water is being conveyed to the air tool? FWIW I use my compressor with a blow gun 99% of the time. When I use it to blow dust off finished wood I never see any water spray, droplets or mist. Draining the tank at the end of the day yields at most a few drops.


Michael Koblic, Campbell River, BC

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In your location, you're not likely to have much trouble. Here in MN, I have to watch out on humid summer days. Painting is near impossible then. Nailers, impact wrenches, welder descalers, die grinders, etc all work with frequent applications of air tool oil to flush the condensed water gunk.

I'm not sure where you're at in BC. Unless you're on the coast, you'd never have the high humidity.


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Karl Townsend fired this volley in news:

I suppose it matters how the cylinders, motor housing, etc. are lined, and what materials are used.

A coalescing type water filter is a _minimum_ precaution for using any and all air tools. One should also have an in-line lubricator for most applications, but it can interfere with some (like painting) so sometimes it's better to hand-lubricate tools if they'll be used lightly.

The only way you can predict how much water will come out is to 1) know the RH, and the exact volume and pressure of the air you've used, or 2) put a filter on it, and measure the water!

I'm in north central Florida. During the spring and summer, I can easily drain a quart of water from my tank in a day of "ordinary use", which ammounts to pumping up the 150-gal tank about ten times during the work day.

I filter and I lubricate, and my air tools last essentially forever in light, non-commercial use.


Reply to
Lloyd E. Sponenburgh

A factor: the size of your compressor tank. A pancake compressor's tank is going to warm up and not condense the water vapor in the tank much faster than a 80 gal tank. The mass of the steel and the surface area both affect it.

As others have said: it depends.


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Bob Engelhardt

For what it's worth, I've never ever seen a water filter at the tool end of an air hose. I'd think any ordinary water filter/trap would be good enough, if it's sized for your system. Where I sit now is about a 5,000 SF fab shop; on one side there's machining, where they take big pieces of metal and cut them up into little pieces of metal, and on the other side there's welding, where they take little pieces of metal and stick them together to make big pieces of metal. ;-)

I'm the detail draftsman/sweeper. ;-)

They use a lot of air; there are two industrial strength compressors; I don't know the spec, but they're about 5 1/2 feet tall.

And they also have an air dryer, which is essentially a heat pump (think "window air unit" but without the air fans) with a chill trap; presumably it takes enough water out of the air that they don't even have to drain the compressor tanks.

But in my not so professional opinion, unless your air tool is getting stuff wet from its exhaust, just the in-line water trap that came with the system should be good enough.

What do your tools say about oil? I can see an oiler at the tool end, because somebody else in the shop would probably prefer clean air.

Cheers! Rich

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Rich Grise

It's not the heat, it's the humidity:

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Cheers! Rich

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Rich Grise

FWIW, I use a little oilless compressor with a water filter about 6' from the end. Without it, I can't spray oil paint. Also, although it doesn't run my palm sander very well, when I do run it without the filter I have to take the cover off and blow the water out before oiling it, unless I run it for a long time and it gets very warm.

I'm in NJ, where it tends to be humid in the summer months.

Reply to
Ed Huntress


He's on the north shore of Vancouver Island.

Nice little town, excellent salt water fishing--lots of slugs in the garden and even a few bald eagles and there.

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I would not spray without a filter. I have some disposable filters but they have a 70 psi limit which makes them unsuitable for nailers.

I do not think putting a filter between the tank and the hose is such a problem but that is *not* what the manufacturers of air tools recommend.

I was going to make a 5' extension with a filter, however, the in-line filter, the hose and the fittings cost more than the nailer! They also weigh almost twice as much. So I guess it's another suck it and see situation (or in this case blow).

I am encouraged by your statement that you are not obsessional about running the sander with a water filter.

As for oiling, both my nailers come with a bottle of oil and recommendation to put 2 or 3 drops into the intake port before starting a job.

Michael Koblic, Campbell River, BC

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Well, I *am* obsessional about opening it up and blowing the water out after I use it. I'm sure it would quickly be wrecked if I didn't.

I first owned that thing (B&D) when I had a big compressor, and I used it a lot. My little oilless doesn't allow it to develop any torque; I can use it only for light finish sanding now.

I'd do that for sure.

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Ed Huntress fired this volley in news:

What the hell did you read to get that, Mike?

ALL air tools call for "filtered, dried, and (sometimes) lubricated air".

I have filters (plural) on my compressor. In line, they create a total line drop of 4psi at 9 SCFM. If you need more air than that, you need a big scroll rig.

Where DID you come up with that?


Reply to
Lloyd E. Sponenburgh

It doesn't appear that your limited compressed air consumption really requires an oil/water separator accessory, but they can contribute to longer life for air hoses and tools. I haven't used any of the newer inline disposable cartridge-type filters.

My primary use of oil/water separators was for spraying automotive refinishing products. These types of separators cause suspended particles and droplets of oil/moisture to be separated and trapped in the bowl, which is drained regularly. Clean air is important for painting when using lubricated piston compressors, to prevent oil/water contamination of the paint products. A final oil/water separator and large cartridge filter are typically located in the paint booth.

The oil/water separators won't cause an airline pressure drop if they are selected to flow a higher volume of air than the tools demand.. generally, separators are rated for flow, by the better quality manufacturers. My separators had 1/2" pipe inlets/outlets, and were rated for much more flow than my air tools or paint guns would consume.

In properly plumbed commercial/industrial air supply applications, all of the pipe is sloped back to the air compressor receiver/tank. As the compressed air cools as it's being distributed, much of the suspended moisture condenses and drops drops out of the air flow, and is supposed to drain back into the receiver, where it's easily drained.

If the air is cooled by the time it reaches the (machine or) end user, much of the moisture has been removed, and a separator is mostly just added insurance against damage from rust scale, water or eventual accumulated oil in the pipes.

In many home shop applications which aren't plumbed with pipe, the user is close to the heated compressed air source.. then as the air passes thru the air hose laying on a cool concrete floor, the moisture begins dropping out of the air flow. Cooling the air will cause moisture to accumulate, and contribute to failure of air hoses from internal exposure to oil and water.

Having overhead pipe giong to several shop locations is very beneficial in terms of convenience and tool performance, and the pipe also increases the air tank's volume. The down pipes at workstations/outlets should be tapped off of the top side of the horizontal supply pipe.. and include a shutoff valve, and a length of drip leg (with a petcock) extending below the tap for a workstation oil/water separator and pressure regulator.. a lubricator and a high-side quick connector are optional. If the hose quick connector is elbowed to point downward, this allows a hose to just drop down to the floor, preventing excessive strain on the ends of hoses.

A handy location for an oil/water separator is in a protective cage on a work cart.. so an air hose can supply the separator nearest the point of use, then the user generally only needs a short section of hose which can be stored on the cart.

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The answer is yes, no, absolutely, maybe, and I don't have a clue.

FOR MY USES, water would just be a hazard by corroding the volume tank on my compressor, and by possibly rusting or corroding innards of tools.

For plasma arc cutting, it is necessary for the air to be dry, dry, dry, as water suddenly injected in a plasma stream has a variety of bad effects.

A tiny bit of water injected into an air stream carrying $700 a gallon paint would not be a good thing, also.

It just depends on what it is you are doing. I intend to put a water filter or dryer on my shop line, but that would not eliminate the tank corrosion issue.

So, I guess it just depends on the work you do, the tools used, and the downsides of a tiny amount of water.


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Reply to
Steve B

OK, I can see how the original statement can be misinterpreted. The air tool (nailer) manufacturers' manuals (Paslode, Bynford etc.) do not object to a filter between the tank and the hose but insist *in addition* on a water filter close to the air tool (see the original post). The first one is no problem, the second one is a hassle. Hence this thread.

Michael Koblic, Campbell River, BC

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mkoblic fired this volley in news:

Yeah... the little "piggyback" filters are a pain, and you can't haul one around with the tool that's big enough to handle the volume. Still, I kind of like one within five or six feet of my gun when I am spraying lacquers .

But unless you have really COLD weather and lousy de-watering at the head end of the line, the amount of water you're going to get out the end of a service hose is minimal.


Reply to
Lloyd E. Sponenburgh

If you're on a roof with a long hose, you could probably get enough pressure/temperature drop to get some condensation, even with a water trap on the compressor. The traps only get the droplets, not vapor. If you add a dessicant drier unit, like paint shops use, then you can get the vapor, too, but not really needed for air tools. Usually it's dry enough here that I blow out dust when I trip the tank drain stopcock, but it has been humid enough that at times that I get water out of a DA exhaust. I have a trap on the compressor, didn't have more than a couple of drops when the DA was dripping. As far as a hassle, I usually run short whips on the tools, a trap and oiler in- line with a male and female quick-connect doesn't take up that much room and don't really affect handling of the tools. They don't have to be plugged directly into the tools' handles, after all.


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