Auto Service World
Feature   October 1, 2000   by CARS Magazine

Up in the Air

A personal FRL gives your air tools a little TLC.


Do you use your air tools much? It’s a question no one has asked for decades, because in today’s tight margin fast-turnover service environment, it’s simply a given. Reliable pneumatic hand tools are as important as wrenches, yet a surprising number of technicians ignore the basic rules of air tool maintenance and operation. Can you get away with it? Maybe, but it’s cheaper and easier to keep pneumatic hand tools in good working order than to repair or replace.

Garbage in, Garbage out

Clean air is something we all appreciate, but for pneumatic tools, “clean” doesn’t come from a catalytic converter. The killer contaminants in shop air come from three basic sources: the compressor, the distribution system, and from the ambient air the compressor draws. Water is an obvious contaminant, and is present in every supply in some amount. Water vapour in the compressor’s intake air becomes a rust-enhancing fog in tank, lines and tools unless removed. If you can see or feel moisture in the air exhaust stream, immediate action is required. If you can’t, however, there still may be a problem. The best case solution is the one the vast majority of shop owners can’t or won’t install: central air drying and lubrication. Why not? Mainly because of the expense; cleaning up compressed air can cost as much as the compressor itself in a medium to larger size installation. The other reason is based on simple need. Most fixed-base and portable shop equipment ships with filter-regulator assemblies as standard equipment, guaranteeing clean air for expensive equipment. With the exception of screens to keep out coarse particles, however, pneumatic hand tools don’t have that luxury, and as a result are subject to whatever comes, literally, down the pipe.

What can the technician do to protect expensive air tools? The first step doesn’t cost a dime, and is the most commonly forgotten basic maintenance procedure: drain the compressor. As the first line of defence against tool damage, get into the compressor room and open the tank stopcock. The foul-smelling air/oil/sludge emulsion in your pail represents the garbage not going into your tools. Take a look at the drained water. If there is a significant amount of white “mousse” the compressor’s rings may be worn, allowing blowby of compressor oil into the supply air. Compressor oil isn’t the same as air tool lubricating oil, and needs to be filtered before the air ratchet or impact gun. Don’t forget to check the compressor’s crankcase sight glass or dipstick while you’re there.

With the compressor drained, take a look at the manifold and lines feeding the bays. Low spots in the system are where the water and debris are, so if outlets are positioned there, moisture, rust and scale will work their way into your tools. A quick fix is to rotate the “tee” fitting so that the outlet points upward, then add a long nipple between outlet and tee, the longer the better. The nipple provides surface area for moisture to condense on and fall back away from the outlet connector. A better solution is to plumb a deep trap into the line before the outlet and equip it with a drain valve. Either way, traps will not take care of suspended droplets and fine particulates. The solution is a filter-regulator-lubricator set, or FRL. FRL’s can be attached permanently or temporarily through quick-connects, but all work in a similar way. Supply air is filtered, passed to a regulator, then flowed to a lubricator where an adjustable amount of oil is metered into the tool supply air. Everyone has seen FRL’s, yet a surprising number of technicians either don’t use them, or use low quality products.

How clean is clean?

The screens commonly found in the tool inlet port suggest that coarse filtration is all that’s necessary, and although it’s true that modern tools will function in dirty air, service life will be affected. Besides moisture, the other tool killers in unfiltered air are suspended particulates and compressor oil. Scale and corrosion particles are often oxides, which are harder than most steels. Particulates work on air tool moving parts in the same way that unfiltered engine oil damages engines: accelerated wear. Ratchets and die grinders (among others) use rotary air motors whose multiple vanes need a tight seal against their cylinder walls. Accelerated vane wear leads to tool power loss, and can deteriorate gradually, without a technician realizing what’s happening. The “sandblast” effect of air flow in high CFM tools not only causes faster wear on sliding and rotating parts, but can speed failure of anvils and other components in impact guns and chisels. Blowby oils from compressor crankcases can swell and deteriorate o-rings and seals, and can “wash out” legitimate air tool oils added by an unsuspecting tech. If you’re careful about lubricating your air tools and still experience power loss or failures, check the exhaust stream. The oil fog there may not be entirely your own. The filter unit in the FRL will have ratings based on the smallest particle size the unit will trap. Usually measured in micrometers (a micrometer is 0.000039 inches) filters rated at smaller than five microns should be avoided. Ideally, the finer the better, but in real world shop conditions, super fine filtration will cause frequent clogging and an unacceptable pressure drop. The filter bowl is usually clear polycarbonate plastic, and may have an automatic or manual drain valve. The need to drain regularly is obvious, but what isn’t so clear is how the tech can determine whether the bowl if full. Dirt and sludge will coat the bowl, so regular cleaning is a must. It’s under pressure, so if your new FRL can’t isolate the filter from the supply line, add a valve upstream to avoid a surprise when you unscrew the bowl. Clean with soap and water, and avoid petroleum cleaning solvents or fuels, especially with plastics.

Do you need the regulator?

The answer to that question is: maybe. If you’re pricing filters and lubricators separately, it’s usually cheaper to buy the entire FRL assembly as a unit and get the regulator “free”, so it will likely be part of the system whether you need it or not. Pressure related problems with air tools are almost always about insufficient pressure rather than too much, and a regulator can’t increase PSI over the supply pressure. Where it can be invaluable, however, is where long piping runs, system restrictions or improper manifolding creates “low pressure zones” on the shop floor. Individual regulators allows higher compressor settings to balance pressures at individual benches and bays.

Don’t forget the lubricator

The last component in the train is the lubricator, and it’s simplicity itself. just fill, set the adjusting knob for the desired flow rate, and forget it. Check with the tool manufacturer’s instructions for flow rates, and watch the oil level. A visible oil fog in the exhaust air is too much, and can reduce tool performance.

If the level doesn’t drop noticeably over a week or two (in a busy shop) then a little more flow is probably indicated. Naturally, air tool oil is the only way to go, and if someone misloads the lubricator with something else (motor oil is a common mistake, as is WD 40) drain and flush the unit immediately.

At anywhere from $50 to $200 for a filter-regulator-lubricator set, the investment makes sense both for high-end air tool users and for technicians who buy low cost “disposable” units, where repair kits may not be readily available.

And how much is downtime worth? It’s essentially a “pay me now, pay me later” proposition: The cost of an FRL beats the price of a rebuild or a light duty backup impact wrench or air ratchet.

Why pay more? SSGM


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