Air Line Lubricators

Air line lubricators are devices used to add a lubricant, via an air line, to a compressed air operated appliance; one that requires an external source of pneumatic oil for proper operation.

Air-line-lubricators usually contain the following parts: the head, an adjusting screw on the head, a bowl to contain the lubricant, and often a bowl drain to allow removal of the lubricating oil when needed.

In the top of the head of typical air-line-lubricators will be a small, transparent housing. This housing will have an adjusting screw on the top. That adjusting screw will increase or reduce the drops of lubricating oil that are being drawn into the air stream by the passing of compressed air through the lubricator head.

The reason that the housing is transparent is so that, as you adjust the flow of oil via the flow-adjusting screw, you can count the drops as you do so.

Item 1

Item 4 in the adjacent picture is the adjusting screw housing.

Item 2

Item 2 is the lubricator head itself. Attached to this head will be a bowl that contains the lubricating oil. The bowl will attach to the head with a bayonet style mount or it might be threaded on. Care must be taken to ensure that the air line is empty before attempting to remove the lubricator bowl.

Note that a lubricator head will usually have an arrow on it displaying the required direction of air flow through the lubricator, and you can see the one on the head of the lubricator in the photo.

In the lubricator head there are ports to which the in and out air lines are attached. Some lubricator manufacturers have line ports that are modular, allowing one lubricator body and head to be used for a number of different port sizes.

---

Resources:

---

Function

As the air passes through the lubricator head the air path is reduced in size which results in an increase the speed of the compressed air. In the narrow part of the head is an outlet for a small tube that extends from the head down into the oil inside the bowl.

Air passing through the venturi inside the head, as noted earlier, speeds up. The faster moving air, moving past the orifice to which the small tube is attached, reduces the air pressure in that tube creating a partial vacuum, and this draws oil from the bowl up the tube.

The oil travels up the tube from the bowl, then through the transparent housing, past the flow-adjusting screw, and then drips back down into the air stream.

Depending on the style of the venturi and the speed of the air, the oil is "atomized" (reduced into fine droplets) to differing degrees. The atomized oil is carried out of the lubricator head and, providing the lubricator is placed close enough, downstream to the application to be lubed by the oil in the compressed air supply.

Item 3

Item 3 in the picture above is a sight glass to allow an operator to check the oil level in the bowl without having to remove it.

Item 4

Item 4 is the lubricator bowl, this one without a drain at the bottom.

There are a number of different styles of lubricators, from a number of different manufacturers. While many of them will function similarly to others, some will atomize the oil into a finer mist or fog, and those types claim to be able to lubricated applications at a greater distance from the lubricator than others.

A Problem With Lubricators

Usually they are installed in an FRL (Filter - Regulator - Lubricator) set which may be quite some distance from the item to be lubricated. The oil-carrying-air has to travel from the lubricator to the application, sometimes through an air valve - without the oil dropping out of suspension.

If the oil drops out of suspension in the air line, then after a while it will fill the air line, and then, in time, a great slug of oil will be transported downstream to the exhaust port of the valve (now it will leak all over the floor) or out the exhaust port of the tool (yup, it will now leak all over the floor here too).

Different manufacturers claim that their lubricators will atomize the oil to different degrees of drop size, so that oil carries farther using their lubricators than those of other manufacturers.

Please note the order of the letters in the acronym F-R-L. It's that way on purpose. First the Filter, then the Regulator and then the Lubricator. Putting the lubricator before the filter will simply fill the filter bowl with oil, and none will get downstream. And, you don't want oil flowing through most regulators either, so the lubricator should always be downstream of the regulator.

Many (Most, anymore?) air valves and air cylinders come from the factory well lubricated for the life of that item. It's only in really high cycles that lubricant may need to be added.

Adding a lubricator to an air line feeding items that are already lubricated from the factory means that the oil that you are introducing will tend to wash out the factory lube, and from then on, you will then have to continuously provide external lubrication for the life of the item. Check with the vendor. For your application, do you actually need that lubricator?

Air tools that have high use rates usually need external lubrication, so an inline oiler should be used for them. You can plumb a small lubricator a few feet (one meter or so) up the air line from the tool, ensuring that lubricant is getting to the air tool.

Air tools used infrequently, and for short periods, can normally be adequately lubricated by dripping 2-3 drops of air tool oil into the in-port of the tool just before use, and then another 2-3 drops with a quick burst of air before putting the tool away until next use.

What Oil?

We used to sell lubricating oil for air line lubricators, by the multiple-gallons. It was always a light, air tool oil.

If you visit the OIL ISSUES page you will links to recommendations and to a short video about compressor oil.

I also wanted to be sure that I made the right recommendation to you as to what oils you could use, so I asked the FRL experts. Norgren was kind enough to provide guide to air line lubricator oils. You can find it here:

www.about-air-compressors.com/support-files/recommended-lubricants.pdf .