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In this comprehensive guide, we'll walk you through the step-by-step process of using a pump/filter cart like HEAT’s PFS-III to efficiently fill your hot oil system. Incorporating a pump/filter cart to your commissioning and fluid management routine is the industry standard best practice for contamination control, fluid quality assurance, and overall system performance.

Here are some of the key reasons to use a pump/filter cart during the filling process of a hot oil system:

  • Contamination Control: A pump/filter cart is equipped with filtration capabilities that help remove contaminants from the fluid being pumped into the system. It effectively filters out particles, debris, and impurities that can negatively impact the performance and longevity of the hot oil system. By maintaining clean fluid, the risk of clogging, wear, and damage to system components is minimized.
  • Air and Moisture Removal: Air and moisture can be present in the fluid during the filling process, which can lead to operational problems like pump cavitation, oxidation, reduced heat transfer efficiency, and component corrosion. A pump/filter cart is designed to facilitate the removal of trapped air and moisture, ensuring a more efficient and reliable hot oil system.
  • Flow Control and Accuracy: Pump/filter carts provide precise control over the flow rate during fluid filling. This allows for a controlled and consistent filling process, preventing overflows or inadequate fluid levels.
  • Mobility and Flexibility: Pump/filter carts are portable and can be easily moved around the installation site. This mobility enables flexibility in accessing different points of the hot oil system, including remote or hard-to-reach areas. The cart's versatility allows for efficient fluid transfer and filtration in various installation scenarios, especially in locations that have multiple hot oil loops.
  • Time and Cost Savings: Utilizing a pump/filter cart streamlines the filling process, reducing the time required for system commissioning. The efficient removal of contaminants and air minimizes the need for subsequent maintenance, repairs, or premature fluid replacement. This ultimately translates into cost savings by extending the lifespan of the hot oil system and reducing operational downtime.


Overall, the use of a pump/filter cart when filling a hot oil system enhances fluid quality, ensures proper system operation, and prolongs the equipment's life. It promotes a smooth commissioning process and helps maintain optimal performance and reliability over time.

Pump Filter Carts can also be used as a low temperature side stream filtration loop to remove particulates and/or water from systems with a relatively small overall volume of fluid (less than 100 gallons) and at temperatures below 150°F.

Watch: HOW TO Fill a Heat Transfer System using a Pump Filter Cart


ALWAYS use the proper PPE. Consult any Safety Data Sheets for the fluid you’ll be working with.

  1. Locate the lowest fill/drain point in the process. It may not be on the hot oil system.
  2. It is important to fill fluid from the bottom up, letting air escape as the process is filled.
  3. Bring the Pump/Filter Cart and oil close to the lowest fill/drain port.
  4. Attach the hose fitting from the Pump/Filter Cart outlet to the lowest fill/drain port.
  5. Attach the cart’s intake hose to the oil source.
  6. Open all internal valves in the process loop. Make sure the valves on the expansion tank sight glass are open.
  7. Place oil catch buckets at each high point air bleed. Plan to have someone stationed at each. If the bleeds are far apart, you might need a radio or walkie-talkie to communicate back to the person operating the pump/filter cart.
  8. Open the air bleeds. Keep an eye on these air bleeds once filling begins.
  9. Open the fill drain/valve and turn on the Pump/Filter Cart to allow fluid to flow in.

Connected to the low point of the system

The tank is filled to 25% at ambient temperature.

High point bleeds are critical to removing air from inside the pipes


  1. Power on the Pump/Filter Cart to begin filling the system with heat transfer fluid.
  2. Monitor the air bleeds. You may hear air being forced out of the loop through the openings. Another way to check if fluid is flowing is to temporarily cover the air bleed outlet with the palm of your hand. Pull your hand away - you might feel a puff of air from the built-up pressure as the fluid continues to push air out.
  3. Monitor the differential pressure gauges on the filter cartridges. If the fluid is contaminated with water or debris, you may have to replace filter cartridges during filling.
    1. To replace the filter cartridge:
      1. Turn off the Pump/Filter Cart
      2. Close the fill/drain valve the pump filter cart is attached to.
      3. Unthread the spent cartridge and replace with new. You can use any combination of water filter or particulate filters.
      4. Open the fill/drain valve.
      5. Turn the pump back on to resume filling.
  4. Fill the system until fluid is visible in the expansion tank sight glass, leaving room for the fluid level to drop during venting.
    • HEAT sizes our expansion tanks so that they should be filled to 25% at ambient temperature. This leaves enough room for thermal expansion when the fluid is at its maximum operating temperature without causing dangerous overflow of hot fluid. Learn more here.
  5. Vent the system using the high-point air bleeds to let air escape. Close the air bleeds when there is a steady stream of fluid coming out.
  6. The level of fluid may drop in the expansion tank sight glass as air escapes. If necessary, add more fluid until the expansion tank is properly filled.
  7. Close all vent valves when a steady stream of fluid comes out.
  8. Turn off the Pump/Filter Cart when the system is filled.
  9. Close the system fill/drain port the cart is connected to.
  10. Leave the pump/filter cart connected to the closed fill/drain port as you begin circulating fluid through the loop. Air may continue to escape through the expansion tank, so more fluid may need to be added.
    • Don’t start heating up the fluid until all air is removed from the system!
  11. If more fluid is needed, open the fill/drain port and turn the pump/filter cart back on to add more fluid. Close the valve when you reach the correct level of fluid.
  12. Lay down some absorbent cloth, then disconnect the pump hose.
  13. Detach the hose fitting from the system drain.
  14. Begin heating up your system!


  1. Allow the system to cool down.
  2. Attach the Pump/Filter Cart intake hose to the system drain valve and output hose to an oil drum or vessel.
  3. Open the system drain valve and turn on the Pump/Filter Cart
  4. Open the vents to allow air to flow in and the fluid to drain freely.
  5. When the fluid from one section has fully drained, turn off the Pump/Filter Cart.
  6. Lay down some absorbent cloth, then disconnect the pump hose.
  7. Detach the hose fitting from the system drain.
  8. Repeat for other zones of the system that still contain fluid.

The pump filter cart is an essential tool for start-up and maintenance of hot oil systems, and is something all heat transfer system operators should own. If you have any questions about commissioning your system or about getting a pump filter cart for your operation, our aftermarket team would be happy to help – give us a call!