Addressing Common Airlock Issues
Guest article by Cem Brinckley, Rotary Airlock, LLC

An airlock could be compared to the water pump on your car: a comparatively inexpensive component of a much larger system that is out of sight and out of mind … until a problem develops.

Though seemingly a small item in the overall picture, an airlock’s failure could result in something as subtle (but still costly) as a loss of efficiency – or the complete shutdown of a production line. It is important, then, to make sure the airlocks are properly functioning and maintained to bring maximum efficiency and run-time to the manufacturing process.

Airlocks in both positive and negative pressure pneumatic systems can experience three common issues. Each issue is examined in detail below, followed by practical solutions to implement.

Seizing Rotor

Of the most common issues with airlocks, seizing of the rotor is at the top of the list. This is not surprising, when you consider that the gap separating the housing from the rotor vanes is only as thick as a sheet of paper.

Aside from the obvious seizing due to an object falling into the airlock, there are three primary reasons why an airlock is going to seize.

1. The first is the result of thermo-expansion. When an airlock is running in an application hotter than it was built for, the rotor can expand into the housing. It is critical to note the clearances of a particular unit, and to be aware of temperature and humidity levels year-round, before installing it. Any temperature spikes that may last for more than a few minutes should be taken into consideration. Regulation of temperatures, and installing insulation around the housing, can be used to protect the housing from thermo-expansion.

2. Product build-up, another reason for rotor seizing, is highly preventable. If the material going through the unit has a tendency to pack or has a high moisture content, it will start to build up on the housing and quickly lock up the rotor. It is a common practice to machine bevels into the vanes so there is less flat on the tips to bind with. However, build-up may persist despite the beveled edges. In such cases, two solutions have proven successful. A new rotor with specially milled vanes with a knife-like leading edge can be installed, and/or an exclusive, highly lubristic chrome plating (developed specifically for the aerospace industry and available through Rotary Airlock) applied to the internals of the airlock may be used.

3. The third most common reason for seizing involves the rotor shifting to either side, galling up the endcaps enough to engage the rotor. This can occur when a drive sprocket is pounded on too hard, moving the rotor over, or when new bearings are installed. To prevent the rotor from shifting side to side, place shims on the opposite side of the rotor when installing the drive sprocket, and remove when finished. When installing bearings, replace both at the same time, since they wear at the same rate. Also, alternate tightening the lock collars on both sides, so that you do not pull the rotor more to one side or the other.

Managing Bearing and Seal Failure

The second most common issue with airlocks is bearing and seal failure. This is especially true of applications that run very fine material, such as flour. The rest of the airlock might be in good shape, but if the seals and bearings fail, it could eventually lead to the rotor dropping into the bore.

There are two ways to address the bearing and seals issue. The first to be aware of is bearing conversions. In the case of inboard bearing airlocks experiencing bearing failure, it is possible to convert the bearing to another type, more suitable to the application. An example would be going from a sealed bearing to an ER style to enable the bearing to be greased.

The second solution to consider is seal conversions. This may involve adding additional seals to existing lip seals, or converting an airlock from rope packing to mechanical seals.

Not Letting Blowby Allow a Slowdown

One more common issue airlocks may experience is blowby. This occurs when an airlock is no longer able to lock out the air, which is now blowing by between the rotor vanes and housing bore. This usually prevents material from being able to efficiently move through the airlock.

When blowby is the problem due to excessive wear or corrosion, there are three areas to address which can aid in obtaining longer life from the airlock. The first to consider is the rotor set-up. For example, if much wear is found on the endcaps, a change from an open-end rotor to a closed-end may be warranted.

Secondly, wear coatings from chrome to ceramics may be considered for the housing and endcaps. Communication is critical between the end-user and the vendor applying the coatings, as some coatings perform better in certain applications than others.

The third area to address is high-wear tipping for the rotor, which goes hand-in-hand with previously mentioned wear coatings. In both cases, knowing the abrasive product going through the airlock is essential. In this instance, that information will help determine what material to use for tipping. Various options include stellite, tungsten, chrome, and AR adjustable blades.

Implementing any of these in-plant solutions, or examining existing equipment to address these issues before they occur, will extend the life of an airlock. Most severe issues can be tackled by an airlock remanufacturing specialist before you need to consider purchasing new.

For more information contact:

Mr. Cem Brinckley
Sales Manager
Rotary Airlock, LLC
707 E. 17th St.
Industrial Park
Rock Falls, IL 61071
Telephone:  800-883-8955
Fax:  815-626-5366
http://www.rotaryairlock.com/

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