Manual for Refrigeration Servicing Technicians - UNEP - Division of ...

3
Refrigerant Management
CHAPITRE 3
PAGE 11
Vapour recovery mode
Vapour transfer
The refrigerant charge can be recovered in vapour recovery mode
as shown in this diagram.
DISABLED
UNIT
Vapour recovery mode
Vapor Side
Liquid
Vapor
SCALE
Drier
Vapor
Liquid
Recovery
Cylinder
RECOVERY
UNIT
On larger refrigeration systems this will take appreciably longer
than if liquid is transferred. The connection hoses between recovery
units, systems and recovery cylinders should be kept as short as
possible and with as large a diameter as practicable.
Liquid transfer
Until recently, it was unheard of to recover direct liquid. But with the
use of oil-less compressors and constant pressure regulator valves,
it’s become the preferred method of recovery by most recovery
Inlet
Outlet
equipment manufacturers. Oil-less recovery equipment has an
internal device to flash off the refrigerant. Oil-less compressors will
tolerate liquid only if metered through a device like a CPR (crankcase
pressure regulating) valve. Don’t attempt to use the liquid recovery
method unless your unit is designed to recover liquid.
Liquid recovery is performed the same way as standard vapour
recovery. The only difference is that you will connect to the high
side of the system. Recovering liquid is ideal for recovering large
amounts of refrigerant.
If the recovery unit does not have a built-in liquid pump or is
otherwise not designed to handle liquid, then liquid can be removed
from a system using two recovery cylinders and a recovery unit. The
recovery cylinders must have two ports and two valves, one each for
liquid and one each for vapour connections. Connect one cylinder
liquid port directly to the refrigeration system at a point where liquid
refrigerant can be decanted. Connect the same cylinder vapour port
to the recovery unit inlet. Use the recovery unit to draw vapour from
the cylinder, thereby reducing the cylinder pressure, which will cause
liquid to flow from the refrigeration system in to the cylinder. Take
care as this can happen quite quickly.
The second cylinder is used to collect the refrigerant from the
recovery unit as it draws it from the first cylinder. If the recovery unit
has adequate onboard storage capacity this may not be necessary.
Once the entire liquid refrigerant has been recovered from the
refrigeration system, the connections can be relocated and the
remaining refrigerant recovered in vapour recovery mode.
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