Gene Vogel
Pump & Vibration Specialist
Electrical Apparatus Service Association, Inc.
St. Louis, MO
In his paper presented at the EASA Convention 2009, Gene Vogel discusses the challenges and considerations involved in using centrifugal pumps to handle extreme temperatures, both high and low. Vogel emphasizes that while these pumps are generally ordinary, understanding the applications and special provisions required can open doors to profitable repair business opportunities.
Centrifugal pumps can typically handle temperatures ranging from -5°F to 450°F (-20°C to 230°C) without special provisions. However, temperatures above 450°F (230°C) and below -4°F (-20°C) require specific modifications. High-temperature applications are common in petroleum refineries and power generation facilities, where pumps handle boiler water, petroleum products, and steam at temperatures up to 860°F (460°C). Low-temperature applications, such as air separation into element gases, involve cryogenic temperatures down to -460°F (-273°C).
Key components sensitive to extreme temperatures include mechanical seals, static seals, pump volute and intermediate housing, bearings, impellers, and alignment. Mechanical seals must be cooled to prevent damage from friction and heat, using methods ranging from simple flush lines to sophisticated external coolers and filters. Static seals must be compatible with both temperature and chemical properties of the pumpage. Pump volutes and housings are often made of stainless steel or high alloy steel to withstand extreme temperatures and pressures.
Bearing lubrication is crucial, as high temperatures can affect oil viscosity and lead to bearing failure. Cooling the oil externally is preferred over direct cooling of the bearing housing. For low-temperature applications, bearing heaters ensure optimal oil viscosity. Impeller clearances must account for thermal expansion and contraction, with close clearances for hot applications and open clearances for cold applications.
Shaft alignment is critical for pumps operating at high speeds, with tolerances often under 0.002 inches (0.051 mm). Thermal growth calculations help determine target values for alignment, considering the coefficient of linear expansion for the pump housing material. Piping strain must be minimized to prevent misalignment and distortion of the pump housing.
Cavitation, caused by liquid vaporization due to pressure drops, is a significant concern for both high and low-temperature pumps. Controlling vaporization requires maintaining sufficient suction pressure, with the Net Positive Suction Head (NPSH) margin being a key factor. High-speed pumps and impeller design also play roles in minimizing cavitation.
Vogel provides examples of extreme temperature pump applications, such as a petroleum refinery coke bottoms pump, boiler feed water and circulating pumps, and liquid oxygen transfer pumps. These examples highlight the special features and considerations required for reliable operation in extreme conditions.
In conclusion, understanding the special nature of extreme temperature pumps allows for informed decisions about entering the repair market. While these pumps are generally ordinary, ensuring proper thermal isolation and functioning of seals, bearings, and alignment is crucial for reliability.
Key Points Covered:
- Temperature ranges for centrifugal pumps
- High and low-temperature applications
- Sensitive components: mechanical seals, static seals, pump volute, bearings, impellers, alignment
- Methods for cooling seals and bearings
- Importance of shaft alignment and thermal growth calculations
- Cavitation concerns and control measures
- Examples of extreme temperature pump applications
Key Takeaways:
- Centrifugal pumps can handle a wide range of temperatures with proper modifications
- High and low-temperature applications require specific provisions for reliable operation
- Cooling methods for seals and bearings are crucial to prevent damage
- Shaft alignment and thermal growth calculations are essential for high-speed pumps
- Controlling cavitation is critical for both high and low-temperature pumps
- Understanding these considerations can open doors to profitable repair business opportunities
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