A “Typical – Atypical” Alignment
A colleague and client of ours called, in a bit of a quandary.
“Ever seen anything like this?” he asked. I had to answer “No, I have not”.
This is a C-face motor. It is typically mounted to a C-face flange, which connects to a vertically oriented pump. But in this case, the C-face motor is mounted to a steel plate, and the pump is a vertically oriented “horizontal” split case pump.
The customer inspected the machine, including an alignment check. Their findings?
- The coupling insert was shredded and replaced.
- The shafts were out of alignment by approximately ⅛”
- The pump bearings were bad and had been replaced recently.
There was not enough clearance in the motor hold down bolt holes to correct the misalignment. Both the suction and discharge flanges of the pump were opened, and there were flex joints on both the suction and discharge sides. This allowed both the motor and pump to be moved.
And now you know as much about it as I do. So, this blog comes with two questions:
- How would you perform this alignment?
- Do you see any other potential issues with this design?
I’m very interested in your thoughts.
Hi Stan, kindly allow me to share. This is treated to be vertical alignment process. It can be aligned uncoupled to facilitate shaft rotation during execution of alignment. Before performing the alignment, there are parameters to look at as identified (as found) such as neck-down the hold down bolts, but this is risky since the cross-sectional area of non-threaded portion of the bolt will get smaller. Enlarging the hold down bolts’ holes while maintaining the bolt-circle diameter (BCD). Provide jack bolts to be located in each hold down bolt (at the flange side). In regard to design issues (since the owner wanted it to be like that) each shaft can be inserted with a bush to act like an adapter to reduce the cantilever effect or change a coupling type with longer and bigger hubs.
Short term – change the motor to be stationary in the alignment to get the shaft centerline, then go back the pump being stationary and should be close enough to shim for proper alignment. If not enlarge the holes a bit and should be good to go. Not my favorite because I doubt the piping is stress free either with expansion joints installed. That pump can withstand a fair amount of piping misalignment with expansion joints though. Normally you dont see them mounted in this orientation, which could be a factor with the bearing failure. Interesting. I could see that whole set up causing issues, obviously vibration due to base “design” of basically cutting a hole in a table. Also the weight of the motor is going to flex that base. I would look seriously at dumping this design and getting something in there that has been properly engineered for reliability. If there isn’t space to install a proper setup and this is what we are saddled with, my first suggestion would be to address the base. I would reinforce the base and stiffen that up, get some impact testing to make sure we arent ringing at the operating resonance. The next thing I would do is get an adapter to mount a C flange to the base, so that the motor is actually sitting on the base it was designed for and could be locked in. We would have to take care we have enough shaft length and coupling to accommodate the increased height. With the pump installed and all piping stresses eliminated, align to locate the motor and weld the C flange adapter to the base. There may be a little vertical alignment on the motor to fine tune, but it would be a much better setup than existing.