These pumps prevent equipment from corroding, provide lower costs and increase efficiency.
by John A. Kozel (Sims Pump Valve Company, Inc.)
August 19, 2015

Engineered composites can be designed and used to improve performance and efficiency as well as reduce maintenance and repair costs. Composite upgrades prevent expensive products from deteriorating, extend the life and reliability of existing equipment, and increase pump efficiency. They can even prevent pump leaks that can result in costly cleanups and fines from regulatory agencies. In most cases, reduced downtime resulting from introducing structural composite pump upgrades is one of the most important benefits.

Structural composite upgrades can extend pump life, improve performance and increase efficiency.Image 1. Structural composite upgrades can extend pump life, improve performance and increase efficiency. (Images and graphics courtesy of SIMS Pump Valve Company, Inc.)

The impeller is the heart of any centrifugal pump. Like a human heart, a pump impeller is the most critical pump component, constantly stressed by hydrodynamic forces, fatigue, corrosion, erosion abrasion, chemical attack and cavitation. The overall efficiency of a centrifugal pump is in direct correlation to the efficiency of the impeller. To maximize efficiency, the impeller's hydraulic design must correspond to the design of the pump casing and to the operating conditions of the pump in service.

Any centrifugal pump can be made energy-efficient by upgrading the impeller and rings to an optimized and engineered composite, such as one company's structural graphite epoxy composite. This company offers impeller and ring upgrades for any centrifugal pump, which provide higher efficiencies and increased longevity. They can also design the impeller so that the operating point becomes the best efficiency point (BEP).

When companies are trying to save money, it may seem difficult to justify the upgrades, but the payback for pump upgrades is extremely quick—usually less than one year return on investment. In most cases, the incremental costs of upgrades are minimal when compared with the loss in downtime, energy and expensive repairs. Plant outages, ship overhauls, building new vessels, constructing new manufacturing plants, plant expansions and new system installations are good opportunities to upgrade existing pumps to composite internals and specify pumps with upgraded efficiency and reliability features.

As equipment starts to age, pumps lose performance and efficiency. They also require additional maintenance, repairs, expenses and downtime. Often, the aging or corroding equipment cannot keep up with plant demand. Before equipment gets to this point, pumps can be upgraded to structural composite to extend the life of the pump, return the pump to the proper performance and increase efficiency.

Pump Optimization

Too often, a pump is purchased for a specific performance but when put into service, it operates at a point completely different from the original design point, or BEP, because of the system requirements. The pump operating away from the BEP also causes problems such as excessive noise and vibration, shaft oscillation, cavitation, and premature wear and failure of the mechanical seals, bearings, rings, sleeves and impellers.

In extreme cases, the pump shaft will break right behind the impeller from the excessive radial forces that occur when a pump is operated away from the original design point.

Two severely deteriorated impellers in a two-stage horizontally split-case cooling pumpImage 2. Two severely deteriorated impellers in a two-stage horizontally split-case cooling pump

Operating a pump away from the BEP has a detrimental effect on pump efficiency. The larger the pump, the more energy is wasted. Operating any pump away from the BEP wastes a tremendous amount of money, because an estimated 85 percent of the total cost of owning a pump is the operational cost (maintenance cost plus the cost of energy). Fortunately, these problems can be easily resolved by installing engineered structural composite impellers and rings, which have been re-engineered for the system's requirements. The reliability and longevity of the complete pump is also substantially improved.

Image 2 shows two severely deteriorated impellers in a two-stage horizontally split-case cooling pump in a power plant. They were underperforming and were terribly inefficient. A 75-kilowatt (kW) motor operating in this condition could easily lose 50 percent of the original efficiency.

If the original efficiency was 80 percent and now the pump is operating at 40 percent efficiency, there would be an approximate loss of $31,104 per year at $0.12 per kilowatt (kW) hour (see Equation 1).

30 kW loss x 8,640 hours x $0.12/kW hour = $31.104
Equation 1

Even if the pump was operating only 10 percent away from the BEP, the approximate loss would be $7,776 per year, plus additional maintenance expenses (see Equation 2).

7.5 kW loss x 8,640 hours x $0.12 kW hour = $7,776.00
Equation 2

The composite pump in Image 4 was re-engineered into a two-stage structural composite pump with single-suction impellers (see page 76). It is approximately 11 percent more efficient than the original metallic pump (before corroding), and this new composite pump will never corrode. All wetted parts are manufactured with structural composite, and the bearing frames are machined from type 316 stainless steel.