BEST PUMP TECHNOLOGY B029
If you ‘re going to purchase a new centrifugal pump you might as well get the best technology available.
Here is a list of some features I think you should be specifying:
- Specify a low shaft diameter to length ratio (less than 60 L3/D4 or less than 2 in the metric system). This will allow the pump to function in a large operating window and it will reduce a lot of shaft deflection that is deadly to bearings and mechanical seals.
- You should use a C or D frame adapter to simplify driver to pump alignment, especially when down time is costly.
- A centerline design will compensate for thermal expansion at the wet end of the pump and eliminate some pipe strain problems.
- An oversized stuffing box will allow the seal to run cooler and last longer in most slurry applications.
- You need adequate bearing retention. Above 65% of its efficiency most centrifugal pumps thrust towards the volute rather than the thrust bearing. A simple snap ring is not good enough.
- Specify positive bearing sealing with a mechanical seal or use a labyrinth seal. Do not use grease or lip seals that will frett or damge the pump shaft.
- Be sure you have reliable bearing oil level indication. To high an oil level is as bad as too low a level.
- There should be connections for bearing oil cooling if it is necessary. Do not allow a cooling jacket on the bearing case outside diameter. This will cool the outside of the bearing, cause it to shrink and increase the loading on the bearing balls.
- You want as low a net positive suction head required (NPSHR) as possible.
- Try to specify a double volute pump to prevent shaft deflection. It’s sometimes difficult to get double volute designs in the smaller pump sizes
- Be sure the suction specific speed number is below 8500 (5200 metric).
- Look for any features that makes dynamic balancing of the rotating assembly easier.
- Be sure you have the correct impeller specific speed number for your application.
- When ever possible the impeller should be manufactured from a duplex metal.
- The impeller should be investment cast and not sand cast.
- It’s desirable to adjust the semi-open or open impeller from the wet end to prevent seal face load change. Look for designs that allow you to do this.