Suction Accumulators; Filter Screens; Sound Shell - Emerson Copeland Scroll YBVH021 1U-3E9 Application Manuallines

NOTE: Since the discharge stub contains a check valve, care must be taken not to overheat
it to prevent brazing material from flowing into it.
3.4

Suction accumulators

CAUTION
Inadequate lubrication! Bearing and moving parts destruction! Avoid
liquid refrigerant returning to the compressor. Liquid refrigerant dilutes the oil,
could wash the oil off the bearings, moving parts and could lead to overheating
and compressor failure.
Application of A3 refrigerants has an impact on the PED classification (Pressure Equipment Directive
PED 2014/68/EU). Select and determine the correct PED classification of refrigeration components,
such as suction accumulators.
Irrespective of system charge, oil dilution may occur if large amounts of liquid refrigerant repeatedly
flood back to the compressor during:
▪
normal off cycles
▪
defrost
▪
varying loads
Due to Copeland Scroll's inherent ability to handle liquid refrigerant in flooded start and defrost cycle
operation, an accumulator is not required for durability in most systems. However, large volumes of
liquid refrigerant repeatedly flooding back to the compressor during normal off cycles, or excessive
liquid refrigerant flooding back during defrost or varying loads can dilute the oil, no matter what the
system charge is. As a result, bearings and moving parts will be inadequately lubricated and wear
may occur.
To determine if the accumulator can be removed, dedicated tests must be carried out to ensure that
excessive liquid does not flood back to the compressor during defrost or varying loads. The defrost
test must be done at an outdoor ambient temperature of around 0°C in a high relative humidity
environment. Liquid floodback must be monitored during reversing valve operation, especially when
coming out of defrost. Excessive floodback occurs when the sump temperature drops below the safe
operation line shown in the oil dilution chart – see Figure 5.
If an accumulator has to be used, the oil-return orifice should be from 1 to 1.4 mm in diameter
depending on compressor size and compressor floodback results. A large-area protective screen no
finer than 30 x 30 mesh (0.6 mm openings) is required to protect this small orifice from plugging with
system debris Tests have shown that a small screen with a fine mesh can easily become plugged
causing oil starvation to the compressor bearings.
The behaviour of the accumulator and its ability to prevent liquid slugging and subsequent oil pump-
out at the beginning and end of the defrost cycle should be assessed during system development.
This will require special accumulators and compressors with sight tubes for monitoring refrigerant
and oil levels.
3.5

Filter screens

CAUTION
Screen blocking! Compressor breakdown! Use screens with at least
0.6 mm openings.
The use of screens finer than 30 x 30 meshes (0.6 mm openings) anywhere in the system should be
avoided with these compressors. Field experience has shown that finer mesh screens used to protect
thermal expansion valves, capillary tubes or accumulators can become temporarily or permanently
plugged with normal system debris and block the flow of either oil or refrigerant to the compressor.
Such blockage can result in compressor failure.
3.6

Sound shell

No sound shell attenuation for YBVH* compressors is available from Emerson at this time. If a sound
shell is still needed, particular attention shall be paid to the electrostatic charge of the insulation
material, which could be a potential ignition source – see EN 60079-0, clause 7.4.
C6.2.38/0719/E 13