rotational vibration

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.

One thought, if it is a square shank pto shaft it could be slide together 90 degrees out, causing all kinds of vibration.

basilisk

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Sorry, I couldn't find a good link. An airblast spray has a huge squirrel cage fan hooked by a gear box and belts to the tractor PTO. the air from the fan is nozzled down so the air leaves at over 200 mph. Takes a lot of horsepower to do this.

I'll try the rotating mass idea by just boltinh a plate to a large pulley. Thanks, I wasn't thinking this simple. Still, if there was some way to have mass with the elastic coupling, it would work far better. i just have no clue how to build this.

I don't know what an air blast sprayer is, but I have used a lot of 540 rpm pto equipment and I have never had that sort of an issue with the PTO shaft itself. My guess is that the problem is deeper inside the machine and not really related to the PTO shaft at all. If you are repairing it "for about the fifth time", It sounds as though you haven't ever gotten to the real problem. Could you contact the mfr about it or a dealer? It may be a common problem.

I guess you have a lot more modern tractor than any of mine. My 60 Hp Case 800 diesel only goes 1450 rpm's at 540 PTO speed. Have you really checked PTO speed? Could it be that you are over revving the sprayer?

Pete Stanaitis

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Karl Townsend wrote:

here's a pic of a similar unit:

A harmonic balancer is the mechanical equivalent of a second-order low pass filter for electrical signals. The differential equations are identical in form. In addition to mass (inductance) and elasticity (capacitance) you need damping (disspation). In a harmonic balancer this comes from losses in the elastic material (typically rubber), or it may come from the load.

So what do you repair to fix the problem? Changing over to 1000 RPM shaft would help if its a PTO shaft problem. You can check that the PTO shaft is telescoping freely. Also check that the tractor PTO shaft and machine shaft are the same height and point at each other.

So this is basically a leaf blower on steroids? Unless something is loose in the drive line, this should provide a very stable drive line loading.

I don't know what your "bolt to large pulley" setup looks like, but if you can have oversized holes in that plate and fit rubber tubing around the bolts that go through it you'll get your elasticity. use a rubber washer on each side of the plate as well and some secure stop like nylock nuts, double nuts with a lock washer between, castle nuts and cotters, etc. so the bolt connections are secure without being over tight.

Ah. Looking at that, it brings up the question of the spray pump. If there is a problem with the triplex pump with one cylinder not working for some reason, you would get a lighter load each time that piston was supposed to be on it's pressure stroke, possibly allowing the flywheel effect of the blower to drive the pump ahead of the PTO drive momentarily with the PTO catching up a fraction of a second later causing the drive line to experience the forward - reverse bucking you noted.

Elastomeric coupling? (page 2): "The flexible element absorbs the unavoidable torsional vibrations..."

I bet this would work real well if I could redesign the drive line to use a coupling. maybe this winter.

Thanks for the link.

Karl

What happens when you change the tension on the fan drive belts? If they are implicated at all, that'll change the resonant frequency. It's a bit far to drive over to Blighty so we can instrument it up and workout where the resonance is :-(

Mark Rand (Did similar work on power station foundations once) ETFM

Put a flywheel on the load side of this and you have a harmonic balancer.

Karl, what is the frequency of the vibration? Is it about 9 Hz (synchronous with PTO speed) or is it considerably lower? If it's lower, and if there is some sort of governor that maintains PTO speed at 540 RPM in presence of varying load, then the vibration might be that governor hunting.

How's you know that??? Yes its right at 9 bangs per second.

BTW, pretty good info in the catalog David found.

Karl

I've never tried that. I keep the eight belts pretty tight, 1/2" deflection in the three foot between pulley spacing. can't go tighter, I'd take out bearings. What do you think running loose would do? Not much margin here, I smoked all the belts once, pretty spendy to rebelt this unit.

Karl

I recommend you closely inspect the spray pump as noted in my other post. If it is a triplex pump like the one on the other unit you posted a link for it could very well produce a "lumpy" torque load if one of the pistons was not functioning like from a stuck inlet valve.

The other thought, is that if this lumpiness occurs once per PTO shaft revolution i.e. 9 times a second, something may be bent, such as the shaft the pulleys are on, causing the belt tension to cycle every revolution.

Karl: I'm not clear on how your system would lose mechanical balance. And I don't know all the variables here but it sure sounds close to my balancing my helicopter rotor which was turning at 500rpm. With an electronic balancer that senses where the rotating item is when the accelerometer, or in our case the velocimeter, reading is maxed, it is relatively easy to determine where weight needs to be added to achieve balance. This is however a simple explanation of a single plane balancing operation. Items with some lateral extent like the cranshaft and flywheel system of a car have two planes to worry about. If a single plane balancer could work for you, most helicopter operations have the equipment. My guess is that you are quite a trip from my zip code 93527. If you were close, I do have a balancer and some experience with it on helicopters.

I'll take a stab at this one. This is a insecticide sprayer, right? If so, that kind of stuff is awfully hard on equipment. It eats at metal and is sticky. Is the fan clean? Could it be nasties built up in the clutch, maybe when on down time leaking in the same position. Bad bearings, that would do it. Sucking air between the tank and pump?

Just someone tring to help that klnows what a Malathion-Methyl-Parathion-Ketone Flop is.

SW