Pumps & Systems, May 2008

In Pumps & Systems January 2007, I wrote an article about cavitation and how a collapsing water vapor bubble can damage an impeller. Since then, I have received a number of requests to address Net Positive Suction Head (NPSH) and its relationship to cavitation. Here it is in a very simple, Pump Ed 101 perspective.

Pumps & Systems, May 2008

In the April issue, we discussed fundamentals of the overhung impeller centrifugal pump design. Its advantages are a single bearing housing and a single seal or packing, but an overhung impeller load is a disadvantage. By placing bearings on both sides of the impeller, a better support is achieved.

Pumps & Systems, May 2008

The South Asian pumps market offers growth potential across the region. Malaysia, Singapore, Thailand, Vietnam, Indonesia, Philippines, Australia and New Zealand (among others) comprise this estimated $1.2 billion market.

Improvements and growth in industries such as chemicals, power and oil and gas are expected to drive the overall market revenues in the area. Furthermore, with environmental regulations increasing demand for high-end, sophisticated pumps, manufacturers must strategize to meet demands for quality, high performance, product development, effective service and competitive pricing.

Pumps & Systems, May 2008

Bolted flange gasket technology continually evolves with new designs and materials that provide more reliable and durable seals. Plant operators can choose from a wide variety of gasket products that meet the needs of each application; however, selecting the optimal gasket product is only half the battle. 

Pumps & Systems, May 2008

Most shaft seals are typically placed in bores made of steel, cast iron or other common ferrous metallic material. These ferrous, or iron-containing materials, are compatible with both metal cased and rubber covered seals. Alternatively, bores made of non-ferrous materials or softer alloys like aluminum require special consideration, especially when subjected to temperature extremes. For instance, when a shaft seal with a carbon steel case is fitted to a bore made of aluminum and exposed to high temperatures, the result is a loose fit and seal failure because of the differential rates of thermal expansion between the steel cased seal and the aluminum housing.

Pumps & Systems, May 2008

Maintaining equipment uptime in a mining operation is essential. For one of South American's largest sulfurated copper mining organizations, unreliability simply wasn't acceptable, so they turned to one seal manufacturer to develop a pump sealing system improvement program using the Six Sigma methodology.

Pumps & Systems, May 2008

In principle, a successful sealing program is centered on tracking performance levels to ensure the reliability of shaft sealing components in process systems. This article focuses on the pumping asset only, less the other capital equipment also considered to make-up a "system." The ultimate goal of a sealing program is reducing the total cost of ownership of the asset for which the seal is installed. The focus should be a "pumping system" approach and include root cause failure awareness.

Pumps & Systems, May 2008

Explore some of the issues associated with vertical pump bearings in general, and nonmetallic bearings specifically. Nonmetallic bearings may not be the best answer in every case but have been an excellent choice for many applications worldwide. In general, these product-lubricated bearings preclude additional contaminants (oils, greases) infiltrating the pumped fluid.

Pumps & Systems, May 2008

For more than 100 years, machine parts composed of mechanical carbon have provided an alternative solution in applications where temperature and atmosphere prevent the use of oil-grease lubricants. Mechanical carbon materials contain graphite, which is relied on for its self-lubricating characteristics. 

Mechanical carbon materials can be an effective solution-and sometimes the only workable solution-for moving/movable machine parts where rubbing must occur with low wear and low friction, and oil-grease lubrication cannot be used.

Pumps & Systems, May 2008

The purpose of a mechanical seal is to prevent leakage but all seals leak to some controlled degree. However, it is important to note that this minimal leakage can be so restricted that specific designs are capable of adequately meeting all emission requirements. Seal failure is defined as excessive leakage. The seal can be described as a controlled leakage device represented by two nonporous, plane, parallel walls separated by a distance h, the seal face separation. Assuming constant physical properties and laminar, incompressible flow, the leakage rate is proportional to the pressure and to the cube of the face separation.