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All About Expansion Tanks

Heat transfer systems play a vital role in various industrial and commercial applications, ensuring the efficient and effective distribution of thermal energy. You can almost think of them as the circulatory system for manufacturing processes. Expansion tanks are key components of these systems and are an essential safety measure for maintaining system integrity, preventing damage and injury, and optimizing system performance.

Expansion tanks are pressure vessels specifically designed to accommodate the thermal expansion and contraction of heat transfer fluids (thermal oil, water, or glycol) as they undergo temperature fluctuations within a closed system. As temperatures rise, fluids expand, creating additional volume that needs to be accommodated. Without an expansion tank, excessive pressure can build up, leading to system failure, leaks, or even catastrophic damage that puts workers at risk.

When installing an expansion tank, it is important to keep these things in mind:

  1. Proximity to Heat Source and Equipment: The expansion tank should be positioned near the heat source without restriction to allow for efficient heat transfer and to ensure accurate monitoring of fluid expansion. Placing the tank close to the equipment also minimizes pressure losses and improves system response time.
  2. Piping Arrangement: Proper pipe routing is essential for the expansion tank's functionality. Position the tank at the highest point in the system to facilitate air removal during initial filling. Additionally, consider installing the expansion tank on the suction side of your pump(s) to prevent cavitation and aid with the  Net Positive Suction Head (NPSH). NEVER isolate the expansion tank from the system with a valve.
  3. Does the tank need to be pressurized? Most of HEAT’s expansion tanks designed for hot oil systems are meant to be open to the atmosphere. However, some applications with temperatures high enough for thermal oil to oxidize if exposed to air need a “blanketed” expansion tank that includes a pressurized inert gas, usually nitrogen. Many water and glycol systems need a “blanketed” tank as well.
  4. Accessibility and Serviceability: Position the expansion tank in a location that allows easy access for maintenance and inspection. HEAT supplies its expansion tanks with a sight gauge for checking fluid levels and fluid condition. Make sure there is sufficient clearance around the tank for routine service tasks.

But how big should the expansion tank be?

Simply put: big enough to accommodate the calculated amount of fluid expansion.

You can calculate this by following these steps:

  1. System Volume Calculation: Begin by determining the total volume of the heat transfer fluid in the system, considering both the piping and equipment. Account for all components, including boilers, heat exchangers, and piping, to ensure an accurate estimation.
  2. Fluid Expansion Coefficient: Every fluid has a unique coefficient of thermal expansion, which quantifies the change in volume per unit change in temperature. Obtain this coefficient from the fluid manufacturer or engineering references to determine the required expansion volume.
  3. Maximum Temperature Differential: Identify the expected temperature difference between the minimum and maximum operating conditions. Multiply this differential by the fluid expansion coefficient to calculate the expansion volume needed.

Now that you know the volume of expansion, HEAT recommends sizing the tank so that when the system is filled with cold fluid, the expansion tank is 25% full. At maximum operating temperature and maximum fluid expansion, the fluid should not exceed 75% of the tank’s volume. Leave a 25% safety volume to make sure that no hot fluid is accidentally drained from the expansion tank’s vent line while the system is running.

Expansion tanks are indispensable components of heat transfer systems – they keep everything in check as temperatures rise and fall, preventing damage to your process. By knowing how to size and where to place expansion tanks, system operators can ensure optimal performance, reduce maintenance requirements, and extend the lifespan of the entire heat transfer system. Adhering to these guidelines will help your engineers and technicians design, install, and maintain reliable heat transfer systems in various applications, ultimately contributing to increased efficiency and operational safety.

If you still have any unanswered questions about expansion tanks or other heat transfer system needs, give HEAT’s experts a call. We are happy to help!