In a message dated 3/4/02 7:03:45 PM Pacific Standard Time, k0wa@swbell.net
writes:
> >Last but not least, I'm also reviving a old MA770. I've got it
> >completely disassembled, and preparing to replace the cable and
> >pulleys. Any advice or knowledge on pulleys and the cables? I've
> >also heard talk about lubricating the cables. Has anyone had any
> >problems in doing so? Has anyone been successful using different
> >pulleys? Any hints and advice on this?
>
These tubular towers work great for their price but it's just about
impossible to lube the cables since they are inside the tower when it's
lowered. I really don't know what you'd do to lube them short of lowering the
tower (too bad if you've got antennas on it) and pulling the sections apart.
Here's part of a chapter I wrote on tower maintenance that pertains to
crank-ups:
Crank-up maintenance
Crank-up towers are complex mechanical contrivances. They have a motor,
gearbox, cables, pulleys, and limit switches - all of which should be
carefully inspected twice a year.
The electric motors and gearbox are generally bulletproof and the only
inspections are to check the oil level in the gearbox, the condition of the
drive belt or chain (some sort of conditioner is helpful for each), and the
operation of the cable drum (there are probably some Zerk grease fittings
that need attention).
Pulleys are sometimes custom made by the manufacturer so you may not be
able to run down to the local bearing store and buy one. Some sheaves are
made by the manufacturer and then an off-the-shelf bearing is inserted in the
middle. This one you probably can replace.
Pulleys need to turn and not bind so a good thing to do is to watch the
pulleys while the tower is being raised or lowered and see if there are any
problems.
Crank-up cables
There are several conditions that would warrant cable replacement. The
first reason is if there is obvious damage or kinking. A kink is a stress
riser and should be inspected closely. Other damage would be where the cable
is flattened.
A second reason for replacing a cable is if there is obvious rust. I'm
not talking about surface rust which is pretty minor, but deeper rust that
may have penetrated the strands and core. Carefully scrape the rusted surface
to see how deep the rust is. If you live close to saltwater or another
hostile environment, you should inspect for this more frequently.
The final reason to replace a cable is if there are broken strands.
According to cable industry standards, you are allowed a few broken strands -
either three in one bundle or six total broken strands in the cable you're
inspecting. So just because you have a few broken strands isn't necessarily a
reason to replace the cables.
Notice I haven't given a time frame for cable replacement like some tower
manufacturers do. It's more a matter of cable condition than it is time. I've
seen cables 20 years old that were in fine shape using the above criteria.
Tower manufacturers might say to change the cables and pulleys every three
years or a similar statement but this has to do more with their liability
exposure and not the actually service life of the hardware.
The easiest way to condition cables is with a cable lubricant. DO NOT use
grease or any heavy oil. A cable lubricant is designed to soak into the cable
and lubricate between all the strands. It does not leave a greasy film for
pollutants and dirt to stick to. Available from <A
HREF="http://www.championradio.com";>www.championradio.com</A> Using grease
actually increases cable failure because it'll trap water inside causing
rapid rusting.
There are two other things you need to do to extend your service life of
the cables. One is to exercise the tower. You should run it up and down a
couple of times a month to work the cables and pulleys. The other thing is to
leave the tower at different heights when extended or lowered. If the tower
and cables are always in the same position (i.e., at a limit-switch stop),
then over time the cable will take a set at that point. A set is a permanent
deformation of the cable. If you leave the tower at different heights, then
the resting cable stresses are spread over more of the cable and minimizing
any potential deformations and failures.
Cheers,
Steve K7LXC
Tower Tech
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