In 1961, the first American Voluntary Standards (AVS) chemical pump was introduced. Since that time, it has gone on to become a highly popular process pump with more than 1 million installations worldwide. The pump has experienced various upgrades since its original release.
When the original article was published in December 1993, upgrades had just been made to the pump, such as increasing the oil sump, making labyrinth seals standard and using a sight glass to monitor oil level. A low-flow version had also been recently introduced. The benefits of all of these upgrades to users are discussed in detail in the article.
Here is a brief overview of changes to the pump since then:
- In 1994, a new seal chamber design provided the best seal environment for single mechanical seals on services with or without solids, air or vapors.
- In 2004, the high-temperature, high-pressure model line offers longer service life and safety features in extreme thermal services.
- 2015 saw the launch of a monitoring device that works as a fitness tracker for pumps and other rotating equipment. This standard feature empowers anyone to safely monitor equipment from a distance using a smartphone or tablet through Bluetooth transmission.
- In 2016, a variable speed pump control solution was launched.
- Finally, in 2017, the 3 x 4-17 pump size was introduced for chemical process applications where net positive suction head available (NPSHa) is low, resulting in 1,800 rotations per minute (rpm) hydraulics at higher heads and lower flows.
Today, chemical manufacturers and users are faced with global competition and pending environmental restrictions that threaten to reduce profitability. The need to reduce overall operating costs has driven pump users at chemical plants to focus on improving reliability and eliminating or reducing fugitive emissions.
The mechanically sealed chemical process pump, which meets American Society of Mechanical Engineers/American National Standards Institute (ASME/ANSI) B73.1M standards, is the workhorse of the chemical processing industries. It will continue to be used on a wide range of process applications—such as liquids containing significant amounts of solids (sodium chlorate, alum, sodium carbonate, chemical wastewater), light slurries (silver nitrate and acetone slurries), viscous liquids (above 150 centipoise [cP], including black liquor and titanium dioxide), and stringy materials where sealless pumps may not be economical to use. In addition to its ability to handle tough services, the flexibility of the design—along with improved low-emission mechanical seals—continues to make ANSI pumps the standard in this field.
To elaborate on why sealless pumps are not economical to handle the above materials, we must note that they use enclosed impellers to reduce the axial thrust and increase reliability. (Although several manufacturers have tried using open or semi-open impellers in sealless designs, many of these have not been reliable at two-pole speeds.) Also, standard sealless pumps have small internal passageways to circulate liquid for bearing lubrication and drive-end cooling, and mechanical seal manufacturers are rapidly improving the reliability of their products while reducing emissions to well below 500 parts per million (ppm). With this in mind, consider the following:
- Enclosed impellers are prone to plugging and premature wear in the above services due to small wear surface area. (Performance and efficiency cannot be renewed without replacing wear rings.)
- Open or semi-open impellers are reliable in these services and are standard for ANSI pumps. (Simple external impeller adjustments allow easy maintenance of performance and efficiency, and there are no wear rings to replace, yielding long-term energy savings.)
- The small internal passageways in sealless pumps are subject to plugging while handling liquids with only small amounts (5 percent) of solids. Viscosity handling is also limited.
- Design solutions separate the pump end from the drive end to allow sealless pumps to handle these services, but these modifications can be expensive and may not be cost effective.
Considering all the facts, it is understandable that mechanically sealed ANSI pumps are the more economical choice to handle these types of liquids.
ANSI Reliability Improvements
To meet emissions regulations and improve reliability, process industries have pushed ANSI pump manufacturers to improve performance. Some manufacturers have formed alliances with users to share technology and improve standard designs. By working together, the theoretical has been combined with the realities of applying pumps on a multitude of services and making them last.