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NOTE: The use of silicon sealant may inhibit the effectiveness of
some types of leak detection equipment.
Intrinsically safe components do not have to be isolated prior to
working on them.
8. Repair to intrinsically safe components
Do not apply any permanent inductive or capacitance loads to the
circuit without ensuring that this will not exceed the permissible
voltage and current permitted for the equipment in use. Intrinsically
safe components are the only types that can be worked on while live
in the presence of a flammable atmosphere. The test apparatus
shall be at the correct rating. Replace components only with parts
specified by the manufacturer. Other parts may result in the ignition
of refrigerant in the atmosphere from a leak.
9. Cabling
Check that cabling will not be subject to wear, corrosion, excessive
pressure, vibration, sharp edges or any other adverse environmental
effects. The check shall also take into account the effects of aging or
continual vibration from sources such as compressors or fans.
10. Detection of flammable refrigerants
Under no circumstances shall potential sources of ignition be used
in the searching for or detection of refrigerant leaks. A halide torch
(or any other detector using a naked flame) shall not be used.
11. 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.
12. 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.
13. Charging procedures
In addition to conventional charging procedures, the following
requirements shall be followed. Ensure that contamination of
different refrigerants does not occur when using charging
equipment. Hoses or lines shall be as short as possible to minimise
the amount of refrigerant contained in them.
Cylinders shall be kept upright.
Ensure that the refrigeration system is earthed prior to charging
the system with refrigerant.
Label the system when charging is complete (if not already).
Extreme care shall be taken not to overfill the refrigeration system.
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