Filling Levels of Pressure Vessels by Volume for Refrigerants

Author: Jarod Hansen

Source Article: Condenser by IIAR
06_Condenser_NOV23_LOW_updated_compressed.pdf (

Filling Levels of Pressure Vessels by Volume for Refrigerants

In the ammonia refrigeration industry, maintaining the proper filling levels of pressure vessels is essential for safety, efficiency, and regulatory compliance. Appropriately filled vessels ensure that ammonia refrigeration systems operate optimally, reducing energy consumption and preventing safety hazards.
“Geographical locations and weather conditions can cause thermostatic or hydrostatic expansion depending on temperatures in the area, which is why we require over-pressure protection,” said Tony Lundell, senior director of standards and safety for IIAR.
Lundell explained that in the refrigeration industry, it is common practice to limit the filling of receiver vessels of any refrigerant to 90% by volume, with a refrigerant temperature of 90°F (32°C). “This has been included in codes and standards for many decades,” he said.
ANSI/IIAR 2-2021 takes a somewhat different approach, recognizing that conditions may vary, and requires that fill volumes be limited to eliminate the risk of hydrostatic overpressure, or otherwise be protected by ASME liquid service relief valves. The traditional value of 90% at 90°F is also provided as guidance.

ANSI/IIAR 2-2021 has the following normative and informative sections:

5.16.2 *Vessel Pump down Capacity. Liquid ammonia shall not occupy a vessel at a volume large enough to create a risk of hydrostatic overpressure unless the vessel is protected by a liquid pressure relief device.

(Informative) Appendix A:
The maximum volume of liquid in vessels has traditionally been considered 90% at a temperature of 90°F. Calculations can be done to determine other levels and worst-case temperatures. If liquid pressure relief is used to protect against overpressure due to hydraulic expansion, the requirement for atmospheric relief is not eliminated if it is required elsewhere in this standard.

6.6.3 *Connection of Ammonia Cylinders. Ammonia cylinders shall not be connected to a refrigeration system unless ammonia is in the process of being transferred by authorized personnel.

(Informative) Appendix A:

Ammonia charging cylinders are not considered part of the closed-circuit refrigeration system. Facility designers are nonetheless urged to consider where and how charging cylinders might be stored. The Compressed Gas Association document CGA-G-2.1 Requirements for the Storage and Handling of Anhydrous Ammonia provides guidance on the topic of storage. The International Fire Code, Section 5003, addresses building requirements for the storage of hazardous materials. Closed-circuit refrigeration systems are not subject to the IFC, Section 5003 requirements.

Lundell added that if a high side pressure receiver vessel is located outdoors and exposed to an extreme seasonal hot climate, operating the pressure vessel at a maximum of 80% would help protect against the lifting of an overpressure protection device due to a thermostatic or hydrostatic increase or fluctuation in pressure.

Carlson & Stewart Refrigeration (CSR) is a full-service ammonia refrigeration company. Our service technicians can help your facility in filling your vessels. CSR can also help in calculating how much ammonia is in the system. If you would like to have more control or monitoring of your system, CSR can help in updating as well.

Scroll to Top