Safety Devices - GEA Grasso M-Series Operating Manual

Description of Design and Function
7.7.11

Safety devices

The following safety devices are fitted onto the SCPs
of the GEA Grasso M-series type series:
Drive motor safety devices
Rated current limitation (016)
The rated current limitation is realised by the com-
pressor control system: When the rated motor cur-
rent is exceeded, the control slide of the compressor
is driven in the MIN direction until the motor current
reaches a permissible level. The normal output con-
trol then comes back into force.
Thermistor (017)
The thermistor shuts down the compressor drive
motor when the temperature of the compressor drive
motor windings exceeds the allowable value.
Pressure-controlled check valve integrated into
the compressor (055)
The check valve function prevents pressure equali-
sation with the LP side of the plant and simultaneous
prevents a reverse rotation of the screw compressor.
Check valve - pressure side (060)
The pressure side check valve prevents refrigerant
from re-condensing in the oil separator.
Oil pressure regulating valve (075)
The oil pressure control valve regulates the differen-
tial pressure between the oil pump discharge side
and the discharge pressure of the package. The oil
pressure control valve is integrated into the OMC-
block (oil management centre).
Safety device to prevent the discharge pressure
from being exceeded
(pressure transducer 105)
The compressor control system switches off the
screw compressor package when the specified limit
value has been exceeded.
Limit value = see parameter list
Safety device to prevent the differential pressure
between the oil pressure after oil pump (pressure
transducer 110) and the discharge pressure
(pressure transducer 105) oil circuit monitoring
from falling too low
The compressor control system switches off the
screw compressor package when the pressure differ-
ence between oil pressure after oil pump and dis-
charge pressure falls below the specified limit value
after a delay period.
Limit value = see parameter list
44
Safety device to prevent the discharge tempera-
ture from being exceeded (resistance thermome-
ter 120)
The compressor control system switches off the
screw compressor package when the specified limit
value has been exceeded.
Limit value = see parameter list
Safety device to prevent the oil temperature from
being exceeded (resistance thermometer 125)
The compressor control system switches off the
screw compressor package when the specified limit
value has been exceeded.
Limit value = see parameter list
The minimum oil viscosity for safe compressor oper-
ation is ≥ 7 cSt. In case of oils that are soluble in
refrigerant, the minimum oil viscosity is to be
ensured depending on the discharge pressure and
temperature, oil temperature, as well as the type of
oil.
Overflow valve (340)
The overflow valve protects the compressor against
impermissible high pressure. The overflow valve
(provided that delivered unassembled) must be con-
nected with the suction pipe on site.
Triggering pressure = see parameter list and P+I
flow chart
The overflow valve is designed in accordance with
DIN EN 13136 "Refrigerating systems and heat
pumps - pressure relief devices and associated pip-
ing - methods for calculation".
Warning!
If not fitted on delivery, the overflow
valve must be connected to the suc-
tion side when installing the SCP in
the refrigeration plant!
Safety valve (345) on the oil separator
The safety valve protects the screw compressor
package against impermissible high pressure.
Triggering pressure = see parameter list and P+I
flow chart
If the screw compressor package is installed into a
refrigeration system comprising an emergency blow-
off station, only the oil separator connection is used.
The valve is available as an option, depending on
the required acceptance.
GEA Refrigeration Germany GmbH | P_261511_1 | Generated 01.04.2015
Operating Manual | GEA Grasso M-Series
Screw Compressor Packages