High Viscosity Fluids
As a general rule of thumb, centrifugal pump performance drops noticeably at 50 centipoise, becoming excessive and impractical at about 200 centipoise. In applications over 200 cP, other pump designs are recommended.
High Differential Pressures
The pressures they are able to produce are limited by their single stage. Multistage pumps, for example, use multiple impellers in series to create higher pressure differentials. ANSI pumps
with traditional curved impeller vanes are limited to a maximum differential pressures of around 300 PSI. There are low flow/high head ANSI pumps with straight vane impellers (Barsky style) that can generate up to 380 psi, but with lower efficiencies. Applications exceeding these
envelopes will need pumps other than an ANSI to do the job
with one machine.
ANSI pump design is well thought out to provide useful, forgiving, and maintenance friendly pumps, but that does not make them the most efficient pump for the application. Centrifugal pumps with a closed impeller design are generally more efficient than a standard ANSI pump. Reciprocating pumps can reach efficiencies greater than 90%. Of course, the conditions need to be appropriate, the system designed properly, and the maintenance staff needs to be on board before trying to capitalize on the energy savings of a positive displacement pump.
ANSI pumps are made for a wide range of applications, compatible with commonly pumped fluids. Their shafts are designed to handle commonly encountered power demands. High density fluids require more power to generate the same head. The pump shaft may be inadequate to impart the power into the heavy fluid and break, even when the flow and pressure ratings of the pump are within acceptable ranges.
High Suction Pressure
ANSI Pumps are designed for applications with reasonable suction pressures, and are generally designed with 150# flanges. Even if the pump is capable of delivering the correct DIFFERENTIAL pressure, the casing may not be adequate for a system that operates at high pressures.
ANSI pumps are bare shaft, frame mounted pumps, meaning they require coupling to a driver and the two pieces accurately aligned after installation and as part of regular maintenance. There are other pump designs (generally used for water and smaller power applications) where the pump is mounted directly to the motor. Referred to as close coupled pumps, they have less versatile seal options and the electric motor is much closer to a potential leaky seal, but they save
space and eliminate
High Temperature Service
Information from some manufacturers seems to indicate that their ANSI pumps can take up to 600°F at reduced pressures. While the pump casings can take the temperature, the machine’s long term reliability suffers at temperatures over about 250°F. Their foot-mounted design causes pump/motor misalignment, pipe strain, and shorter seal and bearing life as the centerline moves
upwards with the added heat. Some ANSI manufacturers have a centerline mounted version for this purpose, but common foot mounted ANSI pump should not be expected to last long in high temperature applications. Even if the manufacturer states it as acceptable
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