Karl Townsend wrote:

"Karl Townsend" wrote in message
anews.com...
I'm repairing the same issue on my airblast sprayer for about the fifth
time. Own something long enough and the same problems keep repeating. the
sprayer has a vibration in it at 2500 tractor RPM, 540 PTO RPM. The
vibration is not like a tire out of balance but its a bucking forward to
reverse. When it gets a little lose, in a few more hours of run it will
damn near shake the tractor off the ground. Its also a natural harmonic
at this RPM, slow down and the vibration goes away. Unfortunately, this
REALLY reduces sprayer performance.

I'm replacing the entire PTO shaft and tightening up the clearance in the
gear box again. if everything is tight, the problem is less severe. The
is working on the symptom, not the cause.

This is a long shot, anybody know about balancing this sort of vibration
or changing the natural harmonic frequency?

Karl



I should have added, this is what the harmonic balancer on an engine is for.
I have no clue about building or designing these. Also there's serious
torque here, 60 horse being transmitted at 540 RPM.

Karl

Since most of us don't have farms / orchards or use these items, a link
to them might help us understand the issue.

The "bucking forward to reverse" description makes it sound like
something is momentarily freeing up and jumping forward only to have the
drive slam into it a fraction of a second later, i.e. uneven loading on
the drive.

Adding rotating mass somewhere in the drive should change the resonant
frequency. Also, you say slowing it down a bit helps, can you speed it
up slightly to change the frequency without hurting performance? bumping
up to 600 PTO RPM isn't likely to critically over speed anything, but
might get you out of the resonant range.

The harmonic dampers on an engine are basically a balanced flywheel
mounted to the rotating shaft via an elastic (rubber) coupling.