I have concerns with a fluid coupling suspended between two gear type couplings, and it was engineered that way. Is this acceptable? I have seen this once before with a nine foot jackshaft on a hydropulper and it was nothing but trouble. Throwing butt-rolls into the pit didn’t help matters either.

No; it only increased displacement. Graph out the entire layout on graph paper along with maximums in both directions to see the full swing. I think you'll see that it over extends the allowable tolerance. Also creates an unbalance.

Waylon,
I am curious what this coupling arrangement is used for and what it looks like. Do you have a web link or other info?

Walt
w_f_strong [at] msn {dot} com

Made a quick drawing.

Waylon,

I would question the use of gear coupling type instead of using diaphram or disk-pack type to control eccentricity. If you have high 1xSS vibration, then inspect both gear couplings for tooth wear. If worn, then consider another type of coupling.

Walt

On the pulper I mentioned we decided to go with a solid flange on one end and an ATRAFLEX insert type coupling on the other end. This appeared to have solved the problem, but there were many other variables such as butt-rolls and misalignment that compounded that problem. I would look at doing something similar, but worry about the coupling being rigidly supported out on the end of the shaft improperly loading the bearing. I have worked with dual shim-pack arrangements, but find that the alignment is very critical is such arrangements if longevity is to be achieved. The current situation is shaking, but I have no vibration tools a present to properly diagnose machine. The issue was brought to my attention mainly because the mechanics were debating over the amount of grease to place in the coupling. Apparently they are thinking they are putting to little. Each time the coupling fails it’s dry and looks like a lack of grease or adequate PM’s. I suspect something a little different. I suspect the grease is being overworked and the lubricant is leaching out of the couplings. I need more evidence, which will come in time. Another thing that bothers me about the arrangement is unlike a solid jackshaft the fluid coupling bearing and seal must compensate for issues that might be introduced into or by this arrangement.

Waylon,

My guess is that the decision to switch to a solid coupling on one side of the fluid coupling will prove to be unwise.

Walt

Like Walt, what are all the varibles? Exact design of the fluid coupling.

And what consideration is there for eliminating one coupling?

What kind of delta temps are we looking at? And the distance between motor and G/B.

Waylon,

If I understand it correctly, this looks like a bad idea to me. Maybe a very bad idea.

How are the shafts attached to the fluid coupling? The most common is with a flexible coupling half bolted to the input and output flanges on the fluid coupling. That makes it like a spacer coupling in that you can unbolt the flanges and remove the fluid coupling.

http://falk.rexnord.com/no-ie.asp

That link has some typical arrangements for Falk's fluid couplings in use with their gear couplings. (This fluid coupling used to be and still may be manufactured for Falk by Sime which is in Sweden I think.)

Hope this helps,

Danny

Waylon, I'd think anybody with a name like Butt-rolls would get thrown in the pit often. TGIF!

Walt, check out this link

http://auto.howstuffworks.com/torque-converter2.htm

We used them on internal combustion engines, directly attached to the flywheel. The two gear couplings look to me like inviting alignment problems.

Waylon,
We had a similar setup. It was a nightmare! The initial setup was a slip on (or draw on) style that had a grid coupling on one end (motor end). We failed a number of couplings and wiped out the gbx input shaft several times. An attempt to solve the problem was made by installing rigid coupling hubs on the gbx input shaft and motor drive end. I can't imagine having gear type couplings on both sides. What happens when the couplings wear? I read somewhere that when a coupling cover osolates, so to speak, around the hub, that it may actually "pump" the grease out of the coupling. I'm not sure if that's true, but I do know that labrynth seals that run eccentric to shaft axis will pump oil out of a bearing housing. Our solution was to install a soft start with a direct coupling. Our best setups with fluid couplings are registered fit hard couplings on both sides.