Lubricators for air preparation
Original article date: October 1997
An important step in processing compressed air is to introduce a suitable amount of lubricant usually oil to enable the operating equipment to perform to its requirements efficiently without excessive resistance or wear. Excessive resistance to motion will result in extra power consumption and excessive wear will result in shortened equipment life.
There are two basic types of lubricator in general use: aerosol (most widely used) and injection pump. Invented by Norgren in 1927 aerosol lubricators were the first type of dependable automatic airline lubrication device. They are available in two main types – oil-fog and micro-fog.
In an oil-fog lubricator the fog produced generally has relatively large oil particles and so will only remain airborne for relatively short distances. As a general rule of thumb the maximum distance an oil-fog lubricator should be placed from the pneumatic device which it is to service is 9m. Large particles are more strongly attracted by gravity and so oil-fog lubricators should not be used in attempting to lubricate a device at a higher level than the lubricator.
The micro-fog lubricator uses a special fog generator to atomise only a fraction of the oil. Because the airborne fog is now made up of only light particles less than about 2um in size gravity does not have the same effect on it so this fog can not only travel uphill but also for long distances and through more complex lead lines without wetting out in the pipe. Micro-fog can also ensure proportionate distribution through multiple lubrication outlets ideal for multiple valve control circuits. It can also be used in applications where only very small amounts of lubricant are required possibly over large distances. By adjustment of the drip rate higher oil delivery can be achieved to match that of an oil-fog lubricator and normal usage rates.
The Micro-fog principle has made possible the appication of aerosol lubrication to general machine lubrication such as bearings gears and chains.
Both oil-fog and micro-fog lubricators include a non-return in the syphon tube to ensure immediate lubrication as soon as the air is turned on. However for some rapidly cycling duties or systems with small stroke cylinders it is sometimes not possible to lubriacte correctly with conventional lubricators. For such applications system modifications such as quick exhaust valves must be employed. Alternatively a bi-directional lubricator suitably located can overcome such problems.
The second type of lubricator the injection oil-pump is a positive displacement device. Because of its nature it cannot continuously deliver lubricant but has particular applications in multi-spindle nut runners where conventional lubricators will split air flows according to passageway geometry. The injection pump will deliver the same amount of lubricant to the application point every time it is cycled. This type of lubricator is often used on conveyor chains where their application will overcome problems of incorrectly located or adjusted conventional lubricators.
Several such injectors can be manifolded together to lubricate at several different points but at the same frequency. Whichever type of lubricant is employed all lubricators are total loss systems in that the dispensed lubricant will reach its bearing surface and be broken down into smaller particles and “lost” as the system is cycled.
The amount of oil which should be delivered in a pneumatic system to provide sufficient lubrication is difficult to determine as all systems are different. Pneumatic devices in a system may require different amounts of lubricant and so equipment manufacturers’ recommendations where they exist should always be followed.
As a general guide for most pneumatic systems an oil output density of 60mg/m3is a good basic starting point. From regular inspection and servicing the optimum setting may be found by increasing or decreasing the amount delivered.
Norgren is launching a comprehensive package of guide books and a hotline to promote its air preparation units otherwise known as FRLs (filters regulators and lubricators). This includes a new publication called “Clean compressed air – the Norgren guide to affective air preparation”)
- IMI Norgren
- Tel: 01543 414333
- Fax: 01543 268052
- www.norgren.com
October 1997