Sorry for the delay and thanks for speaking to your pump engineer for me.
I have spoken to few people who deal with alignment and so on and they also recommend 0.5 mils per inch. One of them is coming around to our factory within the next week or so to give an opinion, which I will take into consideration along with other data I have gathered. Like you, I agree that there should be a limiting factor in the total shaft run-out.
In my opinion these long vertical spindle pumps should be classed as a different type of equipment to the run of the mill slurry pump we sell. Although I have been involved in the field only recently I am aware of that our pumps are designed for a rough and ready environment where they take a lot of abuse over their operational life. Most of our horizontal workhorse pumps are over-designed in that the safety factors on their casings, bearings and shafts are large. It is my understanding that they can withstand situations such as shunting the shaft during start-up to clear the pump of any settled sediment, although I by no means condone this situation as it represents bad operational practice and will lead to structural impeller failure after a time. They can also withstand abuse during maintenance. The impression of our products by our customers is that they are robust in the common understanding of the word. The design emphasis has been on the hydraulics of the pump and material specifications of the wet end components to prolong wear life. Thick steel base supports are typically installed as frames for these pumps to act as a vibration dampener. In the way these pumps have been designed and manufactured this has been the driving methodology behind them and I believe for our typical horizontal pumps it is a winning methodology. The vertical spindle pumps are far more delicate in that, as I explained earlier, they have very unforgiving rotordynamics. The way in which my company manufactures and assembles components for vertical spindle pumps needs to be reviewed if we are to gain a foothold on the problem. It is an interesting design challenge for me and the team I work with because the simple solution of adding a bearing support near the impeller of the pump is not currently feasible because of the corrosive and abrasive environments we operate in.
The shaft and the impeller are our main points of focus. We may stiffen the shaft or lighten the mass of the impeller or both. As I stated earlier, we are also looking at the way in which the shaft is manufactured. If we stiffen the shaft too much we run the risk of moving the first critical in the prime operating region of the pump. We are also looking at how effective heat treatment will be on out shafts, as some of our shafts are only machined near the ends and not across the entire length. We will only be able to make informed judgment on this once we have an effective measurement process in place.
dgallagher thank you for your link to the Bently Nevada article. I have studied it carefully. I have also been looking for API670 and similar documents relating to stuff as well as guidelines local manufacturers in other industries (such as power generation) use.