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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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