Vertical pumps are available in numerous configurations and excel in such areas as ease of multi-staging, virtually unlimited installation depth below grade, and small footprint, i.e., not taking up much real estate. If you have to make a mechanical reliability assessment before releasing your next purchase specification, it might be a good idea to bring it up to 2020 standards.
Consider focusing on the components that experience the most failures: the thrust bearing, seal circulation system, and column bearings. An examination of the overall design from the point of view of the best available configuration, low-risk-of-failure installation, and preventive maintenance practices is not to be overlooked. On cryogenic services, you can involve materials specialists in your review of material selection.
Key Design Elements That Drive Vertical Pump Success
Two areas of overall design are of primary interest. For ease of maintenance, individual column sections should be bolted, not screwed together. Also, impeller attachment using tapered collets should be disallowed on high-reliability vertical pumps.
Preventing failures in vertical pumps starts with design precision, bearing quality, and proactive lubrication practices.
Unless we consider a relatively small size or model, a vertical pump should preferably be equipped with its own oil-lubricated thrust pot instead of depending on the motor thrust bearings to serve the entire assembly. Additionally, we would typically scrutinize the following for industry experience and definable component life:
- The dn-value of the bearings should be within the API-acceptable limit of 500,000.
- Column bearings must be suitable for long-term operation in the medium being pumped. Unless the vendor can demonstrate prior experience, we would enlist the assistance of design engineers familiar with non-metallic sleeve bearings using certain carbon fiber-reinforced perfluoro-alkoxides, likely DuPont’s Vespel CR6100®
- On critically important flammable or toxic services, the preliminary, not yet finalized selection of mechanical seals and their respective support systems would be submitted to the three or four major seal manufacturers at the installation site. These manufacturers would be asked to comment on the reliability aspects of the selection. We expect seal manufacturers to provide feedback on appropriate material selection, pv-values, balance ratios, optimized flush plans, and support system supervisory instrumentation.
- Pump and seal reference locations and the names of contact persons should be disclosed to you, the purchaser. You would then verify data accuracy by communicating with some of the referenced user locations and require that mechanical seals be purchased from the most experienced vendor.
- Vibration probes are a plus on large vertical pumps. They should monitor both high-frequency acceleration and low-frequency velocity. Gradually developing bearing defects will show up in the acceleration spectrum long before there are velocity excursions. During shop testing, the manufacturer and the owner’s inspector should verify the absence of resonant structural vibration.
- A competent pump manufacturer or upgrader will hand-fit keys and provide bottom-radius-ing of keyways. He will not use roll-pins for key fixation. It can be shown that improved shop practices along these lines will increase the shaft factors of safety.
- Arrange for a shop tour of the vendor’s facilities. Observe how workers mount rolling element bearings and point out unacceptable practices whenever necessary.
Enhancing Vertical Pump Reliability Through Effective Lubrication
Some lube-system designs are API-compliant with properly sized water-cooling coils and ISO Grade 68 mineral oils. However, the vertical pump manufacturer may not know the merits of substituting an ISO Grade 32 (equivalent to mineral oil ISO Grade 68) diester or polyalpha-olefin synthetic lubricant.
These synthesized hydrocarbons have greater tenacity (“stickiness”), improved water contamination tolerance, lower pour points, reduced foaming tendency, and greater oxidation resistance than their mineral-oil counterparts.
Inadequate lubrication isn’t just an oversight—it’s one of the leading causes of vertical pump failures.
To get a superior product, a reliability-focused purchaser might explore the feasibility of upgrading both the bearing environment and the lube application. Generally, bearing manufacturers agree that an oil spray introduced into the bearing cage (ball separator) represents the most advantageous lubricant application method.
It dramatically reduces the risk of overheating, a primary concern with some of the customary layouts. In particular, triple-bearing thrust pots are best lubricated by an oil spray that douses the uppermost bearing.
Heinz P. Bloch (1933–2022) was a trailblazer in machinery reliability, maintenance cost reduction, and failure prevention. With over 760 technical papers, 24 books, and seven U.S. patents, he became one of the most respected voices in his field. Bloch’s career spanned roles at Johnson & Johnson, Exxon Chemicals, and as the influential author of Hydrocarbon Processing magazine’s “HP in Reliability” column. A proud NJIT graduate and NCE 100 Hall of Fame inductee, his legacy lives on through his writings, teachings, and the countless professionals he inspired worldwide.
