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Support
oxygen. Air can easily be introduced into the cylinders or systems by not following the correct maintenance and repair procedures.
Air can enter the system by different means. It may be drawn into a system through a low side leak if the suction pressure drops below atmospheric pressure. Air may be already in the refrigerant circuit of the system to be serviced, or it is introduced into the recovery cylinder during the refrigerant recovery and transfer process. The oxygen in air will create a critical combustible mixture at higher pressures with refrigerants.
Before refrigerant recovery, all transfer hoses should be purged or evacuated to remove air or other non condensibles. During flammable refrigerant recovery, do not run the refrigerant circuit into a vacuum! Do not activate the low-pressure override function of the recovery unit. Stop the recovery process at 0 bar to prevent accidental introduction of air. Once the refrigerant recovery process of flammable refrigerant is completed the system should be purged with nitrogen.
Whenever possible and if single substances are used, check the filled recovery cylinder for the existence of non-condensibles by doing a temperature / pressure comparison!
This is done by placing the cylinder in a stable environment for 10 hours or overnight. Measuring temperature of the bottom quarter of the refrigerant cylinder. Place a manifold gauge set on the vapour service valve on the cylinder, open the value and record the pressure. The pressure should correspond with temperature on the pressure temperature chart for the specific refrigerant.
Should the pressure reading be higher than what is indicated there are non-condensibles present in the cylinder. Following all the safety rules applicable to venting flamable refrigerants, vent the non condensibles out of the cylinder until the pressure corresponds with the indicated temperature indicated on the chart.
Marking of recovery cylinders with flammable refrigerants. The cylinder containing recovered refrigerant should be marked to note any special conditions, For example‘ HC R-290 – Recovered’. A red band on the shoulder or top of the container should designate flammable compounds, or mixtures that could become flammable in the event of a leak.
Stanley, I hope that this helps with your understanding around venting flamable refrigerants. I will continue with the recovery process in the next edition. RACA
Grant Laidlaw
REFERENCES: 1. ACRA 2. The Deutsche Gesellschaft für Internationale
Zusammenarbeit GmbH, 3. Testo
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RACA Journal I May 2025 www. refrigerationandaircon. co. za