Many plants use both ANSI pumps and API pumps. However, it can sometimes be difficult determining the right pump to use for certain applications. Some people end up buying ANSI Durco pumps for tasks that require API pumps. It is important to understand the difference between the two types of pumps to help you make wise purchase decisions.
The ANSI Pump
The design of an ANSI pump meets the requirements of the American National Standards Institute. ANSI pumps have become the most preferred end suction pumps. This type of pump can be used to pump chemicals, water, and other substances.
The API Pump
API pumps meet the criteria set by the American Petroleum Institute for general refineries services (standard 610). These pumps are almost exclusively used in oil refinery industries because of their pressure and temperature resistance features.
The Service Considerations
Industries in both chemical and petrochemical sectors consider many factors in their operations. Other than environmental impact and the pumping efficiency, personal safety must also be considered. Therefore, consider operating conditions and the properties of the pumped fluids when choosing between ANSI pumps and API pumps.
The pump packing and casing design rating of ANSI and API pumps vary:
• The rating for ANSI pumps is 300-psig at 300-deg F
• The rating for API pumps is 750-psig at 500-deg F
This makes API pumps more preferable for high temperature and high pressure applications than ANSI pumps.
Both pumps have a single radially split casing design. This design helps to ensure easy maintenance. Majority of ANSI pumps and a few API pumps engage one volute design inside their casing passages. However, many ANSI pumps and some API pumps feature a single volute design on the inner parts of their casing. This is especially true for smaller pumps with low flow rates and impeller speeds. The rate of discharge from the impeller is usually proportional to the area of the volute. This creates a constant velocity at the impeller’s periphery.
Most large API pump designs have a double volute to reduce loads applied on high head and high flow units. The reduction is possible through balancing loads in each volute. This may cause a decrease in efficiency but the pumps have an increased long-term reliability.
Back Cover Arrangements
The back covers of API and ANSI pumps are secured differently. In an ANSI pump, the gasket and back cover is held to the casing by a bearing frame adaptor usually made from cast iron. This back cover arrangement causes a gap to form between the pump casing and frame adaptor that may permit uneven torques of the bolts. As a result, the adaptor may fracture if the casing is exposed to high pressures. An API pump design has the back cover directly bolted to the casing, which does not affect the pump casing’s pressure boundary.