I have another question on a Hoffman blower. We had this particular blower completely overhauled last May. It has been running in the green and good, averaging about .125 ips velocity. Then all of a sudden the drive end vertical Velocity started climbing. As of this morning .387 ips

No bearing faults noted, or impacting nor looseness. Machine feet are all tight. Of course all of these blowers have those hard rubber shims under the frame, and the bolts are loose as they should be at the bottom of the frame. The only thing I can see that could be a factor is that this blower was shut-down 1/22/07 and operations restarted it last month. That is when I noticed the increase. All other points are well in the green zone...Unless maybe the frame has settled in the year since it has been re-installed, causing this increase in 1X...

Any nibbles on this one?

Thanks,

Rod,

maybe something with the coupling? If it is a geartooth, it could have lost its lube and locked up. If it is a metal disc take a look at the shimpack with a strobe. Also check if the pads are overcompressed or broken. Check for 180 degree phase shift across the coupling if misalignment is questionable.

Good Luck

Check filter and see if operations made any changes. Blowers can do funny things when these items are dirty or process has changed. How long is the shaft? Could the blower wheels caused a bow?

It has a shim pack Thomas 350 model. I strobed it last week, looked ok...The shaft is only about 7 inches long. I haven't really gotten in to the frame shims yet, but maybe tomorrow...Unfortunately this particular blower does not have an air filter on it. It sucks air in direct from a 12" inlet with a China Cap on top it and screen mesh...

Guess I can take some phase readings, but looking at the spectrum it doesn't look like an alignment problem. VVEL spectrum has a
.358 ips 1X, no 2X, and .030 ips 3X Looks like a darn imbalance problem.

I hate these kinds of problems, they just keep haunting me, the blower next to it is doing the same thing...

Rockin',

If both blowers share a common pipe header or foundation and both have 1xSS vibration in vertical direction, then perhaps you have a natural frequency causing amplification.

Walt

I haven't looked at Hoffman blowers in a while, but the Roots blowers used to have a design that used a stub shaft attached to the rotary lobe. The result was that it didn't take much of a hickup to cause a bent shaft.

Just throwing out a possiblity... For what ever it is worth.

I thing I do a lot of is "see if I can make it go away" (or change). In this case, I would get some wedges and insert them at various locations along the base, starting at the inboard feet of the blower. You could use some steel plate with some "door shims" available at Home Depot or Lowes. I like the new "composite" shims as they are flat and uniform. I also have some small nylon wedges that I keep in my tool bag and use on smaller motors and pumps.

If you can "make it change" then you know it's not balance. It can shed light on what's going on when you have something weird like this.

Yes, I sometimes do the same thing, but mostly with fans, and motors slide bases. We use metal wedges here, which I can experiment with, but I hate to get too deep with this blower while it's running.

I forgot to attach these yesterday...

Heres the trend

Like Danny said, if it's a gear coupling, check it out. What kind of condition is the screen mesh in? We've all seen weird stuff happen, think it might have sucked up a bird?

I don't like the designs either, not having filters that is. Sort of like sucking up something in the intake of an aircraft. Saw that happen on occasion when I was in the AF. We used to get bat strikes.!

Rod,

Just because there is little at 2 and 3 x running speed doesn't eliminate misalignment as a possibility.

Phase behavior is a key factor in diagnosing shaft related vibrations.

Two weeks back I had a shim pack coupling failure. High vertical and 180 cross coupling phase. After removal shimpack found cracked. Phase afterwards 40 degrees.

Hope phase could help.