Publicité
Les langues disponibles
Les langues disponibles
6. Leak detection methods
The following leak detection methods are deemed acceptable for systems containing
flammable refrigerants.
Electronic leak detectors shall be used to detect flammable refrigerants, but the
sensitivity may not be adequate, or may need re-calibration. (Detection equipment shall
be calibrated in a refrigerant-free area.) Ensure that the detector is not a potential source
of ignition and is suitable for the refrigerant used. Leak detection equipment shall be set
at a percentage of the LFL of the refrigerant and shall be calibrated to the refrigerant
employed and the appropriate percentage of gas (25 % maximum) is confirmed.
Leak detection fluids are suitable for use with most refrigerants but
the use
of
detergents containing chlorine shall be avoided as the chlorine may react with the
refrigerant and corrode the copper pipe-work.
If a leak is suspected, all naked flames shall be removed/ extinguished.
If a leakage of refrigerant is found which requires brazing, all of the refrigerant shall be
recovered from the system, or isolated (by means of shut off valves) in a part of the
system remote from the leak. Oxygen free nitrogen (OFN) shall then be purged through
the system both before and during the brazing process.
Removal and evacuation
When breaking into the refrigerant circuit to make repairs – or for any other purpose –
conventional procedures shall be used. However, it is important that best practice is
followed since flammability is a consideration. The following procedure shall be adhered
to:
• Remove refrigerant;
• Purge the circuit with inert gas;
• Evacuate;
• Purge again with inert gas;
• Open the circuit by cutting or brazing.
The refrigerant charge shall be recovered into the correct recovery cylinders. The system
shall be "flushed" with OFN to render the unit safe. This process may need to be
repeated several times. Compressed air or oxygen shall not be used for this task.
Flushing shall be achieved by breaking the vacuum in the system with OFN and
continuing to fill until the working pressure is achieved, then venting to atmosphere, and
finally pulling down to a vacuum. This process shall be repeated until no refrigerant is
within the system. When the final OFN charge is used, the system shall be vented down
to atmospheric pressure to enable work to take place. This operation is absolutely vital if
brazing operations on the pipe-work are to take place.
Ensure that the outlet for the vacuum pump is not close to any ignition sources and there
is ventilation available.
Charging procedures
70
Publicité
