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Pneumatic lubricators for compressed air systems

Pneumatic lubricators aren't commonly used for compressed air systems today, but they still serve a purpose for specific applications and settings.

Wade Wright, Cross Company
05/28/2017
Image courtesy: Bob Vavra, CFE Media

Image courtesy: Bob Vavra, CFE Media

Image courtesy: Bob Vavra, CFE MediaLubricators have been used in compressed air systems for many years. They are the "L" in filter/regulator/lubricator (FRL). They are designed to introduce oil as a vapor into a compressed air system. However, if you observe new machines that use compressed air, you will notice that these devices are hardly ever used anymore. Why is this?

Early pneumatic products like valves and cylinders used natural rubber and other materials for seals. In fact, leather was often used for cylinder rod seals. Have you ever heard the term "packing?" These materials required oil lubrication in order to seal effectively and reduce friction. This is why lubricators exist—to provide a consistent supply of oil to seals on valves and cylinders.

Modern pneumatic seal material

Seal materials have come a long way. The most common material now used for seal material for pneumatic components is Nitrile, which is a synthetic rubber copolymer. Some seal manufacturers also add products like Teflon to their Nitrile blends to provide additional lubricity. This allows the seal to operate effectively without additional lubrication. Also, manufacturers of pneumatic products add special greases to the seals during assembly. These greases are designed to coat the surfaces that come in contact with the seals, and they are designed to resist drying out or degrading.

When are pneumatic lubricators necessary?

There are still a few pneumatic products that require internal oil lubrication. Anyone who uses a pneumatic tool understands that light machine oil must be added periodically. Additionally, some air motors and air clutches also require internal oil lubrication. If you need to use these products, you will have to figure out a way to get them lubricated periodically.

Use a pneumatic lubricator if you intend to use a pneumatic product that requires internal lubrication. Then, try to use it so that you only lubricate the device that requires it. Why lubricate the entire system when only one device needs it? In fact, depending on where you locate the lubricator in the system, the oil may not ever make it to the device that needs it.

Remember: the oil is suspended as a vapor in the compressed air stream. If the air must take a circuitous route to reach the intended device, the oil may come out of suspension before it gets there.

There are other factors to consider as well.

These are important considerations. Many machines have had performance issues directly related to poor lubricator maintenance and adjustment. If the lubricator runs out of oil, the oil inside the system will tend to dry out, causing many pneumatic products to stick or slow down. If improper oil is used, it can damage the entire pneumatic system. If too much oil is used, it tends to come out of the system exhaust where it can create puddles of slippery oil or oil vapor in the atmosphere.

When are lubricators unnecessary?

Pneumatic lubricators used to serve an important purpose in a compressed air system. Advances in seal material have minimized their importance. If a new machine that uses compressed air is being designed, then the lubricator isn't needed. If a device requires internal lubrication, then the lubricator needs to be installed so that it only supplies oil to that device. If the user wants to lubricate the entire system, then the lubricator should be installed in a location that is highly visible and easy to maintain. You should also consider providing documentation with your machine that clearly states the correct setting for the device, the maintenance schedule to check oil level, and a recommendation for the correct oil to be use. 

Wade Wright is pneumatic product manager for Cross Company Motion Solutions. This article originally appeared on Cross Company's Motion Control Solutions blog. Edited by Chris Vavra, production editor, Control Engineering, CFE Media, cvavra(at)cfemedia.com.

Cross Company is a CSIA member as of 5/13/2017.

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