Amin Almasi
Pump engineers should always consider the balance of costs and benefits.

Pump engineers should always consider the balance of costs and benefits. Practical constraints should always be properly weighted in the sizing and selection of pumps. Many academic and research and development (R&D) works on pumps are not speculative, but focus on dealing with the basic constraints of pump systems.

The operation of the pump system should be entirely reliable and safe, even when operated nonideally. Certain pump systems may be given slightly more flexibility with respect to targeted reliability, but the pump industry is price sensitive and conservative.

A major problem observed with many academic and R&D approaches to selection, design and sizing is a lack of grasp on price. Balancing cost, reliability, robustness, delivery time and operability is the essence of engineering.

The next most important academic/theoretical mistake is to assume a pump on-site will outperform the one in the theoretical simulations or vendor shop tests. This may happen in rare cases, whereas the opposite situation is vastly more common.

How to Select, Design & Size

The selection and sizing process with pumps usually consists of selecting, from several candidates, the option most likely to be high-performance, safe, cost-effective, reliable, robust and properly operable. Coming up with the options is a creative process that involves the use of imagination and the application of different engineering skills and experiences, including reviews of past successful experiences and similar references. The selection of candidates is, however, often more of a set of routine engineering and design works. The key to successful selection, design and configuration is understanding the problems well enough to be able to predict the desired outcome will be reliably attainable.

Capturing information about how past selection and configuration of pump systems have performed and the factors associated with success is important. Operational outcomes, reliability, safety knowledge and risk assessments are also needed. Engineers should minimize both costs and risks.

Pump standards and specifications exist to keep design and operational parameters in the range where the final pump system is most likely to be safe and to work. They also serve to keep documentation comprehensible to fellow engineers, operators, maintenance staff, etc.

Professional judgment is important. This allows engineers to semi-intuitively discern approaches to problems. They will summarily discard avenues a beginner or junior would waste time exploring and include options beginners or juniors would be unlikely to think of.

Caution in Selecting New Technologies

Care should be taken when dealing with new technologies and new pumps. I have been assigned in different capacities to evaluate new technologies and innovative pump systems.

The promotional materials and catalogs I was issued have been proven over time to be wildly optimistic, and since then I have been professionally instructed on several occasions to report on why these pumps and technologies subsequently proved not to work as well in practice as they had in simulations.

How Operators End Up With Poor Design, Sizing & Selection

Professional engineers usually use a combination of explicit and tacit knowledge, founded over many years of experience by as thorough an analysis of the sizing/selection envelope as is practically possible. However, there are some risks and dangers. What if the engineers responsible do not have proper knowledge and experience for the sizing and selection of the specific pump system? What if they follow textbook formulas and guidelines blindly?

Specialists and experienced engineers may complete all steps and stages correctly, but nonspecialists may not. For instance, specialists tend to add far more buffering capacity to pumps, machineries and equipment than nonspecialists to deal with the variability in flow, pressure, operation and the increased possibility of unscheduled maintenance. This may seem slightly more expensive initially, but this investment pays for itself through cost-effective, trouble-free operation.

In a pump package, all machinery, parts and equipment should work together across the full operation range. This is a key aspect of the design, and the full picture should be considered for the sizing, selection and overall configuration of the pump package.