By Pat Kennedy
In North America, there are many older pumping installations that are still in operation. It is not uncommon for centrifugal pumps commissioned in the 1950s, ’60s and ’70s to still be in service.
As this equipment ages, spare parts and replacement pumps become obsolete. In cases where parts are available, prices can be extremely high, and deliveries prohibitively long. At times, the original manufacturer no longer exists, making matters even more difficult.
When confronted with delivery and price problems, customers are forced to consider replacing the older pumps with current line offerings. This can be a costly option. In most situations, the new equipment will not have the same footprint as the existing. In order to install the new pumps, baseplate, motor and couplings will also need to be purchased. Piping and concrete work will also be required.
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An alternative to outright replacement is to reverse engineer/duplicate existing parts. Major components or complete pumps can be manufactured this way by companies such as Emnor Mechanical Inc.
In recent years, there have been advances in technology that make the reverse engineering process more accurate than ever before. Portable coordinate measuring machines can be used to create 3D models of either new or worn cast parts. Enmor uses a probe type machine to measure samples. It generates a 3D model of the impeller. This is then checked for accuracy versus the sample part. In the case of used parts, the model will be adjusted to accommodate for wear.
For pump impellers, the following steps are taken:
- The solid model is used to determine hydraulic geometry and vane angles.
- Using the pump curve, inlet angles are calculated and compared to the solid model.
- Head calculation based on speed, design flow and impeller exit geometry is compared to actual head.
- The impeller solid model is then corrected for wear.
In a similar manner, when casings are worn, inlet area and inlet angles are calculated, and the solid model adjusted for wear.
Emnor also uses portable scanning equipment, either on its own or in conjunction with the probe device. The scanning equipment is helpful when making site visits to measure parts that cannot be sent out. It speeds up obtaining the cast profile shape.
Once the solid models are finalized, the manufacturing process can begin. Most parts produced by Emnor are cast in sand foundries, and require pattern tooling. The pattern is used to create a cavity in a sand mould, into which liquid metal can be poured. After being poured, the casting is cleaned and heat treated if required.
The solid model of the part being manufactured is adjusted for foundry shrink, and machining allowance is added. Once this is done, the pattern tool can be designed. The tools are cut on computer numeric control machines. When the pattern is complete, it is inspected versus its solid model. Corrections are made if required.
In cases where parts need to be made quickly, a combination of 3D printed sand cores and single use tooling is used. When using this process, foundries can be working on moulds in one week.
Whether employing traditional or 3D core methods, Emnor uses melt simulation software. The program uses algorithms to predict liquid metal behaviour as it is poured into a mould. To detect and prevent possible casting flaws, velocity and solidification are checked. If problems are detected, the mould design is corrected. This technology helps eliminate common problems such as shrink and porosity.
One customer was operating two large double suction pumps that had been in service since the 1960s. The casings were badly worn. The cost to replace the pumps with current offerings was prohibitive due to civil, piping and motor requirements. Emnor manufactured two new casings and impellers, that were drop in replacements, at a much lower cost.
Portable advanced technology has made the reverse engineering process speedy, accurate, reliable and cost-effective. When considering whether to replace older equipment, manufacturing drop in replacements is a viable option.
Pat Kennedy is with Emnor Mechanical. This article appears in ES&E Magazine’s October 2017 issue.