Doweling Motor and Pump

Post 1 & 2 are both very helpful. However you seem to be proposing dowelling the motor directly to the pump, whereas the article quoted is for doweling the pump to the base plate pedestals, which is quite different as the motor is then free to be moved for alignment purposes.

You are looking at quite a big pump, is your motor supported on a pedestal or is is bolted directly to the pump? How is alignment (move the pedestal, move the pump etc) achieved and does the motor fit into spigots etc.

These things need to be looked at carefully before you decide to dowel anything. As gringogreg says, if you are going to do it then make sure alignment is good before drilling and reaming. Also ensure that this alignment is repeatable for future overhauls.

The pump and motor is vertical and pump is fixed and motor is moved for alignment. After alignment we just bolt it tight. peridically we check bolts torque as well. Our OEM says that dowelling is not a solution for alignment to be out after running as bolts are tight.

So I am not clear about will dowelling will help or not. The media is sea water. and temperaures with load will not vary much. may be from 30 to 60 c. Motor winding temperaures are in range of 80 C. Will expansion be there to move alignment out during loading. Some times due to low tide the pump(may be 8 - 10 m) down in pit sucks water with sand or dirt. This also gave vibration in flow direction measured on motor NDE. Our motor DE bearing housing clearance also increased and out of 8 on 2 or 3 motors sleeving was done DE bearing.

I kind of agree with your OEM. If the bolts remain tight then loosening of the blots is not the cause of your misalignment. Dowelling does allow for very accurate relocation, but it makes adjustment for alignment due to other tolerances/variables impossible.

I would not do it.

Alignment can be a tricky task. There are many variables that can contribute to poor alignment or apparent good alignment that goes bad for no apparent reason. The following factors have to be considered.

1. Bearings. The type and condition of both motor and pump bearings and their housings. (I presume it is, but if the motor is not designed for vertical operation, the bearing wear and or load can result in problems.)

2. Shaft condition. Are both pump and motor shafts straight within tolerances allowed by both manufacturers? Are the coupling mounting areas true and within proper tolerance for the coupling?

3. Couplings. Is the coupling that's employed specific to the application? That is, for vertical installation, hp, and tolerances of both pump and motor, torque, rpm, etc.

4. Housing/Foundation. Are the mating surface faces perpendicular and normal to the shafts? This is very important and often overlooked as it is assumed by most that they are.

5. Impeller. Is the pump impeller balanced to mfg. spec.?

All or any of the above can be amiss when performing an alignment and the resulting alignment, depending on the ones doing it, will appear to be within specification.

As far as doweling goes, it is best to use tapered dowels. If the taper is properly reamed then the tolerance of the dowel fit is never in question. It is also easier to re-ream the hole if necessary at a later time.

So will misalignment during running condition can be stoppped by dowelling? COMMENT, is some body doing alignmentg checks every year by decoupling the motor and pump...as a PM.

So will misalignment during running condition can be stopped by dowelling?

Not necessarily as it depends on what the cause of misalignment or improper alignment procedure is. As in my previous comment, an alignment can appear to be correct and quite often the coupling and other components will absorb the discrepancy, but over time and load, the arrangement will exhibit problems or fail. Doweling will aid in maintaining the alignment in terms of potential sheer between flange faces and allows for a greater ease of realignment (if all parameters remain constant) when reassembling after disassembly.

is some body doing alignment checks every year by decoupling the motor and pump...as a PM.

At the very least, you should be checking and or replacing the coupling components on a regular PM interval. When doing so it is the time to check alignment.