TECHNICAL INFORMATION
SCREW COMPRESSORS GRASSO SC
Types C ... XF
LUBRICATING OILS FOR SCREW COMPRESSORS
1
LUBRICATING OILS FOR SCREW COMPRESSORS
1.1
Lubricating oil selection list
pressors special refrigeration oils have to be used.
The selection depends on the refrigerant, viscosity
(at least 7 cSt for oil temperature before entering the
compressor), evaporating temperature (pour point)
and requirement made of the oil separation behaviour (flash point, viscosity).
Special refrigeration oils must be used for Grasso
screw compressors. The selection of the oils depends on the chemical properties of the oil, the refrigerants, the operating conditions of the plant and
the required oil viscosity during startup and run. On
request with Grasso also different than in the table
indicated oils can be used. For refrigeration com-
M
*
M
AB
PAO
E
PAG
Basis of the lubricating oils and used abbreviations:
Mineral oil
Mineral oil with special treatment (hydrocracked oil)
Alkylbenzene
Polyalphaolefin
Polyolester
Polyalkylglycol
Table 1: Lubricating oils for R717 (Ammonia)
(recommended especially if minimum oil carry-over from the oil separator is important)
Manufacturer
Type of oil
Basis
Shell
Pour point in
°C
M
*
68
226
-40
CP 1008-68
M
*
64.9
240
-39
Klüber Summit RHT
68
M
*
62
230
-35
M
*
68
232
-39
M
*
58
236
-42
1)
Shell Clavus S 68
Petro-Canada Reflo 68A
1)
Flash point
in °C
CP 1009-68
CPI
Klüber
Lubrication
Viscosity at
40°C in cSt
*
TEXACO
Capella Premium
M /PAO
67
262
-42
Paramo
Mogul Komprimo
ONC 68
M
*
68
230
-33
TOTAL
Lunaria NH 68
M
*
68
230
-36
Remarks
Hydrotreated
for R717 only
Product no longer available.
Refrigeration / Grasso
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03.08.2011
1
TECHNICAL INFORMATION
SCREW COMPRESSORS GRASSO SC
Types C ... XF
LUBRICATING OILS FOR SCREW COMPRESSORS
Table 2: Lubricating oils for DX Chiller with R717 (Ammonia)
Manufacturer
2
Type of oil
Basis
Viscosity at
40°C in cSt
Flash point
in °C
Pour point in
°C
CPI
CP 412-100
PAG
98
226
-40
Fuchs
Fuchs Reniso PG 68
PAG
62
230
-35
Shell
Shell Clavus SG 68
PAG
73.5
>250
-48
Mobil
Mobil Zerice S32
AB
32
154
-33
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03.08.2011
Remarks
Please contact
Grasso
Refrigeration / Grasso
TECHNICAL INFORMATION
SCREW COMPRESSORS GRASSO SC
Types C ... XF
LUBRICATING OILS FOR SCREW COMPRESSORS
Table 3: Lubricating oils for R717 (Ammonia) and R22
Manufacturer
Type of oil
Basis
Viscosity at Flash point
40°C in cSt
in °C
Pour point
in °C
Remarks
Icematic 299
M
56
180
-34
Icematic 2294
PAO
69
233
-60
for R717 only
CP-4600-46
PAO
46
268
-51
for R717 only
Zerice S32
AB
32
154
-33
Zerice S68
AB
68
174
-27
Gargoyle Arctic SHC 226E
PAO
68
266
-45
Gargoyle Arctic SHC NH 68
AB/PAO
64
211
-54
Gargoyle Arctic 300
M
68
200
-42
Gargoyle Arctic C Heavy
M
46
195
-42
Reniso S68
AB
68
190
-33
Reniso Synth 68
PAO
68
260
-57
Reniso KS 46
M
46
195
-42
Reniso KC 68
M
68
200
-39
1)
M
44
195
-39
1)
M
65
205
-36
1)
M
44
195
-39
Shell Clavus G68
1)
M
65
205
-36
Shell Refrigeration Oil S4
FR-V 46
AB
46
180
-42
Castrol
CPI
for R717 only
MOBIL
for R717 only
Fuchs
Shell Clavus 46
Shell Clavus 68
Shell Clavus G46
Shell
for R22 only
for R717 only
Shell Refrigeration Oil S4
FR-V 68
AB
68
190
-39
Shell Refrigeration Oil S2
FR-A 46
M
46
218
-39
for R22 only
TOTAL
Shell Refrigeration Oil S2
FR-A 68
M
68
232
-39
Lunaria NH 46
M
46
226
-36
for R717 only
Lunaria SH 46
PAO
44
252
-51
for R717 only
Lunaria FR 68
M
68
175
-34
for R22 only
AB/PAO
62
245
-54
for R717 only
Petro-Canada Reflo Synthetic 68A
1)
Product no longer available.
Refrigeration / Grasso
_165520_ti_sc_gbr_1_.doc
03.08.2011
3
TECHNICAL INFORMATION
SCREW COMPRESSORS GRASSO SC
Types C ... XF
LUBRICATING OILS FOR SCREW COMPRESSORS
Table 4: Lubricating oils for R134a; R404A; R407C; R410A; R507
Manufacturer
Viscosity at
40°C in cSt
Flash point
in °C
Pour point in
°C
68
250
-39
Icematic SW 220
220
290
-26
Solest 68
64
266
-43
125
262
-27
Solest 220
216
271
-27
Reniso Triton SE 55
53
270
-51
80
275
-39
Reniso Triton SEZ 100
91
288
-39
Reniso Triton SE 170
170
260
-24
220
240
-38
64
250
-54
93
280
-45
66
230
-42
94
230
-42
68
230
-36
105
250
-30
100
270
-30
150
272
-36
Type of oil
Basis
Icematic SW 68
Castrol
Remarks
E
CPI
Solest 120
E
Reniso Triton SEZ 80
E
Fuchs
Reniso PAG 220
PAG
1)
Shell ClavusR68
1)
Shell Clavus R 100
Shell
Shell Refrigeration Oil
S4 FR-F 68
E
Shell Refrigeration Oil
S4 FR-F 100
EAL Arctic 68
MOBIL
E
EAL Arctic 100
Planetelf ACD 100FY
TOTAL
E
Planetelf ACD 150FY
1)
for R134a only
Product no longer available.
Hint!
When using high-viscosity oils with high refrigerant solubility after initial fill of the plant a sufficient mixture from refrigerant and oil has to be provided before start-up the screw compressor.
4
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Refrigeration / Grasso
TECHNICAL INFORMATION
SCREW COMPRESSORS GRASSO SC
Types C ... XF
LUBRICATING OILS FOR SCREW COMPRESSORS
Table 5: Lubricating oils for natural gas and hydrocarbon compounds
Manufacturer
Type of oil
Basis
Viscosity at
40°C in cSt
Flash
point
in °C
Pour
point
in °C
BP
Energol RC-R 68
M
67
234
-30
CP-1515-68
65
224
CP-1515-100
103
260
62
229
CP-1516-100
92
260
CP-1516-150
153
260
60
271
106
271
69
241
CP-9001-100
108
260
CP-1507-68
62
231
89
260
85
226
-45
177
229
-41
M
68
240
PAG
185
260
-30
For natural gas and propane
Shell Gas Compressor Oil S4 PV
PAG
190
262
-30
For natural gas and propane
TOTAL
Primera LPG 150
PAG
142
280
-48
For natural gas, propane and volatile hydrocarbons
Klüber Summit
Summit NGSH100
PAO/ E
140
250
-46
For natural gas, for feed gas control compressors for gas turbines
and hydrocarbons
PAG
CP-1516-68
CPI
CP-4601-68
CP-9001-68
-34
for feed gas control compressors
for gas turbines
For heavy hydrocarbons, for hydrocarbon cooling applications in
range of high pressure/ low temperature
PAG
Glygoyle 11
MOBIL
PAG
Glygoyle 22
Comptella Oil S68
Shell
1)
Madrela Oil T
1)
For propane refrigerant plants or
volatile hydrocarbons, where the
danger of stronger dilution or condensation does not exist
For high temperature application
and for feed gas control compressors for gas turbines
M
CP-1507-100
for natural gas compression
For heavy hydrocarbons, where
strong dilution or condensation will
occur
PAO
CP-4601-100
Remarks
For natural gas and propane
For natural gas
Product no longer available.
Refrigeration / Grasso
_165520_ti_sc_gbr_1_.doc
03.08.2011
5
TECHNICAL INFORMATION
SCREW COMPRESSORS GRASSO SC
Types C ... XF
LUBRICATING OILS FOR SCREW COMPRESSORS
Table 6: Lubricating oils for CO2 application
Manufacturer
Type of oil
Basis
Viscosity at
40°C in cSt
CP-4600-68
CPI
CP-4624-46F
Shell
*
Pour point
in °C
PAO
Remarks
immiscible
68
46
CP-4624-68F
Fuchs
Flash point
in °C
68
*
complete miscible
278
Reniso C 85 E
E
Reniso C 130 E
E
*
136
-27
Reniso C 170 E
E
*
170
-30
attend to the
miscibility gap
Clavus SG 68
PAG
73.5
-48
partially miscible
only
>250
During application of Polyolester: t oil inlet ≤ t discharge - 4K
Hint!
When using high-viscosity oils with high refrigerant solubility after initial fill of the plant a sufficient mixture from refrigerant and oil has to be provided before start-up the screw compressor.
6
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Refrigeration / Grasso
TECHNICAL INFORMATION
SCREW COMPRESSORS GRASSO SC
Types C ... XF
LUBRICATING OILS FOR SCREW COMPRESSORS
Table 7: Use of O-ring elastomers in screw compressors depends on refrigerant and lubricant:
Oil
Refrigerant
M
M*
1)
M*/PAO AB
E
PAO
AB/PAO
PAG
HNBR
CR
-
HNBR
CR
HNBR
R717 (ammonia)
CR
1)
CR
R22
CR
-
-
CR
CR
-
-
-
R134a, R404A, R407C, R410A, R507, R23
-
-
-
-
HNBR
-
-
-
R290 (propane), R1270 (propylene)
-
-
-
-
-
HNBR
-
HNBR
R744 (Carbon dioxide CO2)
-
-
-
-
HNBR HNBR
-
HNBR
Abbreviations used for the elastomers:
CR Chloroprene (Neoprene caoutchouc)
HNBR Hydrogenated nitrile butadiene caoutchouc
1)
shaft seals only with O-rings of HNBR-composition
Hint!
If natural gas and hydrocarbon compounds are used as compression medium (Table 5; page 5), please contact Grasso for O-ring elastomer type.
Hint!
•
The pour point describes the cold fluidity of an oil and represents a non-guaranteed guide
value for the minimum evaporating temperature. [The pour point is defined as the temperature at which the fluidity of an oil decreases to an extent that it does not leave a jar within
5 sec under certain conditions.]
•
Compressors are equipped with suitable elastomers at the sealing point, which are selected dependent on the refrigerant and lubricant. (Table 7; page 7)
•
When selecting the type of oil, the compatibility of the sealant material used in the compressor for o-rings (elastomer quality) must be taken into consideration in addition to the
refrigerant. (Table 7; page 7)
•
Not all the listed oil types can be used for an existing compressor. It is absolutely necessary to assign the oil grade depending on the elastomer used, even if the refrigerant is the
same.
•
Oil grades are not always compatible with each other (cannot be mixed).
•
Changing from one oil type to another can lead to disruptions in the operation of the compressor and to leakages at the sealing points. The compressor manufacturer should always be contacted before changing the oil type.
Refrigeration / Grasso
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03.08.2011
7
TECHNICAL INFORMATION
SCREW COMPRESSORS GRASSO SC
Types C ... XF
LUBRICATING OILS FOR SCREW COMPRESSORS
Caution!
8
•
The lubricant viscosity range downstream of the compressor given in data sheet
must always be observed. At the same time, it must be noted that refrigerant/oil combinations are possible in which, dependent on the pressure and temperature in the oil
separator of the package, the refrigerant dissolves in the oil. This leads to a reduction
of the viscosity of the pure oil and to the formation of foam when the solution equilibrium is altered due to pressure reduction or temperature increase. In this case, the oil
must be cooled by a minimum temperature difference, which is calculated in the compressor selection programme for the given operating conditions. The compressor may
only be operated if the oil entry temperature is complied with in accordance with the
compressor selection programme!
•
The oil separation behaviour of the types of oil given in the Table can vary greatly (e.g.
influence of oil vapour pressure, oil viscosity, solubility, discharge temperature).
_165520_ti_sc_gbr_1_.doc
03.08.2011
Refrigeration / Grasso
TECHNICAL INFORMATION
SCREW COMPRESSORS GRASSO SC
Types C ... XF
LUBRICATING OILS FOR SCREW COMPRESSORS; HINTS FOR SELECTION OF
REFRIGERATION OIL
1.2
HINTS FOR SELECTION OF REFRIGERATION OIL
The properties of the refrigeration oil have an influence on the operation of refrigerating plants with oil-flooded
screw compressors, as it cannot be excluded that residues of the refrigeration oil get into the refrigerant circuit
despite the use of highly effective oil separators. For this reason, when selecting the oil the following should also
be considered
•
a sufficient lubricity of the oil at the bearing points of the screw compressor (minimum oil viscosity with consideration of the solubility of refrigerants in oil depending on both the pressure and temperature),
•
the vapour pressure of the oil for a proper separation behaviour in the oil separator,
•
a sufficient fluidity of the oil at both the evaporating and suction temperature,
•
the requirements upon the miscibility of the liquid phases of the refrigerant and the oil (miscibility gap).
The refrigerant used, the operation conditions and the specific plant design all determine the required characteristics of the refrigeration oil.
At present, five different base oil brands are used:
1. Mineral oils for ammonia and R22
2. Polyalphaolefins for ammonia and CO2 (R744)
3. Alkyl benzene for ammonia and R22
4. Polyglycol (PAG-oil) for ammonia, CO2 and R134a
5. Ester oil for R 404A, R 134a, R 507 and CO2 as well as other refrigerant blends such as R410A and R407C
Besides the pure base oil components other blends of mineral oil and alkyl benzene or of polyalphaolefin and
alkyl benzene can also be used.
The characteristics of the refrigerants regarding the oils mentioned are very different.
Thereby 2 fundamental requirements are needed from the refrigerant and refrigeration oil:
a) Minimum oil viscosity of 7 cSt, maximum 70cSt, at the compressor inlet with consideration for the refrigerant solubility in oil
and
b) Miscibility of both liquid phases of a certain portion of the oil (approx. 1 to 2 %) and the refrigerant.
Besides the requirement of a sufficient viscosity of the lubricating oil, the discharge temperatures in the compressor must be high enough to enable a subcooling of the refrigerant-laden oil by at least 10 K in order to prevent
foaming in the compressor in case of decrease in pressure and/or increase in temperature, before the oil gets to
the bearing points. The basic requirement b) is not met by mineral oil, alkyl benzene and polyalphaolefin in connection with ammonia, as there exists a miscibility gap of 100 %, and neither a solubility of the refrigerant vapour
in the oil nor a miscibility of liquid phases is given. Nevertheless these oils are preferably used in NH3-plants. Oil
fine separation stages prevent greater portions of the oil from getting into the refrigerant circuit.
The base oil versions mentioned will bring about differing oil carry-over rates as the flash points of the oils cited
differ greatly from each other (lowest flash point of alkyl benzene at approx. 160 °C, highest flash point of polyalphaolefin considerably above 200 °C).
Although the fluidity of the oil is characterized by the pour point indicated by the oil manufacturers, the base oil
brands mentioned above feature different VT-characteristics so that at the same initial viscosity of say 68 cSt,
there may arise differences in viscosity at low temperatures in the evaporator in the range of approx. 1500 and
20000 cSt at -20°C.
Refrigeration / Grasso
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03.08.2011
9
TECHNICAL INFORMATION
SCREW COMPRESSORS GRASSO SC
Types C ... XF
LUBRICATING OILS FOR SCREW COMPRESSORS; HINTS FOR SELECTION OF
REFRIGERATION OIL
With relation to oils, the refrigerants feature the following properties:
•
Ammonia
With the exception of PAG-oil, ammonia is not soluble with other lubricants. However, mechanical intermixing
is very intensive so that the oil always carries along ammonia. Due to the low portion of the ammonia the lubricity of the oil will not be changed. The miscibility between the liquid phases of oil and refrigerant is not given. For this reason, an efficient oil separation is required.
•
HFC (e.g. R134a, R404A, R507)
HFC's possess no chlorine and are not limited in their application. Ester oils are used for these refrigerants.
The higher solubility of these refrigerants in ester oil has to be considered when selecting an oil as the initial
viscosity of the oil might drastically change due to the refrigerant dissolved in the oil. However, the fluidity of
the oil in the evaporator is given due to proper miscibility over a wide range.
The most important properties of the main oil groups are described in the following:
1. Mineral oil
Naphthenic base mineral oils are most suitable for refrigeration systems, but paraffinic base oils are also
used. Due to special treatment (dewaxing) paraffinic base oils have more or less the same properties as
naphthenic base oils. Mineral oils are characterized by a relatively low miscibility with HCFC’s (e. g. R22) at
low temperatures. Mineral oils feature a relatively high viscosity index and a low vapour pressure (higher flash
point) whereby oil carry-over is positively affected.
2. Alkylbenzene (also known as alkyl benzole)
Alkyl benzenes represent synthetic oils produced from natural gas. They are characterized by high miscibility
with HCFC’s (e.g. R22) even at lower evaporating temperatures. Alkyl benzenes feature higher thermal stability than mineral oils (use of ammonia in piston compressors). Due to the lower flash point, however, they have
a tendency to heavy foaming in the oil separator and to higher oil carry-over. After changing from mineral oil
to alkyl benzene it should be recognised that alkyl benzenes have a considerable cleaning effect causing in its
turn the filters to clog faster than usual in the time immediately after the oil change.
3. Polyalphaolefins
Polyalphaolefins represent synthetic oils of high chemical and thermal stability. Therefore, they are preferably
used in compressors operating at high discharge temperatures e.g. in heat pumps. Polyalphaolefins are also
employed in ammonia systems. The very low pour point permits very low evaporating temperatures. The high
flash point of the polyalphaolefins leads to smaller oil carry-over rate.
Attention: The high aniline point of polyalphaolefins causes a relatively high shrinkage of O-rings
with CR material whereby leakages may occur even at static seals, when mineral oils or alkyl benzenes are replaced by polyalphaolefins.
Shrinkage can be avoided is synthetic oil blends comprising polyalphaolefin and alkyl benzene are used. In
case of use of pure PAO-oil the Grasso compressors will be equipped with HNBR-O-rings, which do not
shrink when in contact with the oil.
4. Ester oils
In contrast to mineral oil, alkyl benzene and polyalphaolefin ester oils are soluble in the new non-chlorinated
HFC’s (R 134a, R 404A, R 507 etc.). Therefore, the ester oils are the only lubricants at present which may be
used for the HFC’s. Ester oils possess a higher flash point whereby the oil vapour portion from the oil separator and hence the oil carry-over rate are favorably affected. Ester oils are hygroscopic. They absorb water
when getting in contact with the atmosphere. For this reason, ester oils have to be stored in closed tanks. Prior to oil charging, the compressor has to be thoroughly evacuated.
10
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Refrigeration / Grasso
TECHNICAL INFORMATION
SCREW COMPRESSORS GRASSO SC
Types C ... XF
LUBRICATING OILS FOR SCREW COMPRESSORS; HINTS FOR SELECTION OF
REFRIGERATION OIL
5. Polyglycol oil
Polyglycol oils are ammonia soluble and very hygroscopic. That’s why the same requirements have to be imposed as when handling ester oil. When selecting the oil take into consideration the reduction of viscosity
caused by the refrigerant dissolved in the oil. Check the fluidity of the oil in the evaporator with consideration
of the miscibility between the lubricating oil and refrigerant at the corresponding evaporating temperatures.
PARAMETERS USED FOR OILS:
Specific density
The difference in specific density between the refrigerant liquid and the oil may be of interest for oil return. In
this case it should be considered that alkyl benzene has a lower specific density than mineral oil and polyglycol has a higher specific density than mineral oil. The method for specific density measurement is described in
DIN 51757.
Viscosity
According to ISO standard 3448 lubricants are classified in viscosity grades indicated as ISO VG numbers.
The ISO-no. is a nominal guide value only, i. e. the actual viscosity may vary in certain ranges (DIN 51562).
The viscosity indicated refers to 40 °C and to 100 °C.
Viscosity index
The viscosity index gives the relationship between the change in viscosity depending on the temperature (ISO
2909). A high viscosity index means smaller changes in viscosity at temperature changes as compared to a
low viscosity index.
Flash point
The flash point indicates at which temperature the vapours escaping from a heated cup may be ignited over a
flame. The method of measurement is described in ISO 2592. Oils with high flash point have a low oil vapour
pressure. This will enhance the possibilities of oil separation from a compressed gas in the oil separator and
reduce the oil carry-over rate from the compressor into the plant.
Pourpoint
The pour point is the temperature at which the fluidity of an oil decreases to an extent that under certain conditions it will no more leave a jar within 5 sec. According to ISO 3016, the pour point temperature is 3 % lower
than the measured temperature. The pour point is interesting for working oil/refrigerant combinations which
are not soluble with each other. Oils having a low pour point can be returned to the suction side more easily
than oils having a high pour point. The practice, however, shows that oils may be used even at evaporating
temperatures lower than the pour point without any operating problems.
Floc point
The floc point indicates the temperature at which liquid R12 with the addition of 10 % oil will show turbidity by
wax particles precipitating from the oil when chilled (method of measurement according to DIN 51351). The
floc point is of interest when oil and refrigerant can be mixed. The floc point indicates that an oil contains but a
few wax particles and that plants employing HCFC (e. g. R22) can be operated at low evaporating temperatures. When wax precipitation from the oil takes place, problems are to be expected at the expansion valve or
at the regulating valves. For ester oils a critical solution temperature is given measured with a mixture of 10 %
oil and 90 % of R134a. The critical solution temperature is the temperature at which the oil completely precipitates from the refrigerant (non-standardized value).
Aniline point
The aniline point indicates the temperature at which the oil concerned shows a homogenous mixture with pure
aniline. The aniline point is the measurement of the quantity of unsaturated carbon which can be found in the
oil. It is an indication of the compatibility of different sealing materials coming into contact with the oil (method
of measurement according to ISO 3977). Most lubricating oils possess a low aniline point. Neoprene and chloroprene will swell. For this reason, O-rings have to be replaced after disassembling. Polyalphaolefin has a
high aniline point causing neoprene to shrink. (use of HNBR required).
Refrigeration / Grasso
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11
TECHNICAL INFORMATION
SCREW COMPRESSORS GRASSO SC
Types C ... XF
LUBRICATING OILS FOR SCREW COMPRESSORS; HINTS FOR SELECTION OF
REFRIGERATION OIL
Neutralization number
The neutralization number gives the acid content of an oil and is determined by titration with potassium hydroxide solution (KOH). The value is given in mg of KOH per g of oil (method of measurement according to
DIN 51558). Fresh oils should have a low neutralization number.
Hints for oil change
Prior to changing the oil brand or the manufacturer of an oil, consult the compressor manufacturer for advice
to prevent problems in plant operation. In case of incompatible oil brands precipitations from the oil can occur
which might lead to problems within the plant (oil filter, lubrication of bearings, oil return not guaranteed). If,
however, it should be necessary to employ another type of oil, it is of vital importance to remove all the oil
from the plant and to thoroughly clean both the compressor and oil separator (if possible, perform additional
scavenging).
Oil selection table
All oils permitted for the Grasso-screw compressors are given in the oil selection table. Depending on the
specific conditions of a plant consider the above technical features when selecting an oil.
TABLE: Refrigerant – oil compatibility
Ammonia
(NH3)
R22
R134a
R404A
R407C
R410A
R507
CO2
Mineral oil (M)
x
x
NO
NO
NO
NO
NO
NO
Polyalphaolefins
(PAO)
*
NO
NO
NO
NO
NO
NO
*
Alkylbenzene
(AB)
x
x
NO
NO
NO
NO
NO
NO
polyglycol
(PAG)
*
NO
NO
1)
NO
NO
NO
NO
*
Ester oil
NO
x
*
*
*
*
*
*
M + AB
x
x
NO
NO
NO
NO
NO
NO
x
NO
NO
NO
NO
NO
NO
NO
PAO + AB
x = suitable, use of CR-O-rings
* = suitable, use of HNBR O-rings
NO = not suitable
NO
12
1)
= not suitable except refer Table 4 page 4.
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Refrigeration / Grasso