During the past few years Sabroe Refrigeration has experienced a number of problems with mineral oils, particularly in R717 plants. The problems can be divided into two groups: 

The problems have been seen with several mineral oil brands, often occuring within a few operating hours and resulting in severe consequences for both compressor and plants. Following the careful investigation undertaken by Sabroe Refrigeration during the past few years, it has been decided to introduce a range of synthetic oils which can fulfil the demands of modern refrigeration plants. 

Mineral oils may continue to be used in refrigeration plants, providing the lubricating quality is  carefully monitored. For modern, high capacity refrigeration plants, where long lifetime for both lubricants and moving parts is expected, Sabroe Refrigeration  recommends the choice of synthetic lubricating oils. The application areas and specifications for these synthetic oils can be found in the following pages. Installers and/or users are at liberty to choose either Sabroe Refrigeration's own or alternative oil brands which fulfil the necessary specifications. 

General

This recommendation only deals with the lubrication of the compressor. The performance of the lubricant in the plant (receiver, evaporator, etc.) must, however, also be taken into consideration. Lubricating oils with relatively high viscosities must be used to ensure satisfactory lubrication of refrigeration compressors. To obtain the best lubrication, the oil must:

Stratification

It should be noted that in certain plants, particularly with HFC and HCFC refrigerants, the oil may stratify into layers in the refrigerant receivers and evaporators at certain operating conditions and at particular oil concentrations.The Oil recommendation diagrams for SABROE compressors for HFC and HCFC will indicate the limits for Sabroe oils at which this stratification occurs. The oil concentrations stated in these diagrams must not be exceeded. This will enable suitable oil rectification/return systems to be designed to balance with the compressor oil "carry-over" so that the maximum concentration is not exceeded.

For area A in the diagrams, the max oil concentration in liquid phase must not exceed 2%. For the other area, the max. oil concentration must not exceed 5%. For area B: please contact Sabroe Refrigeration. 

Plants with several different compressor types/makes 

In plants comprising several different interconnected compressor types and makes, it is strongly recommended that all compressors should use the same type of oil. This is essential where automatic oil return systems are employed. If it is intended to change the oil from one type to another, please refer to the Oil changing on SABROE compressors later in this publication.  

Selecting the lubricating oil

There are a number of operating diagrams for the selection of lubricating oils for Sabroe compressors operating with various refrigerants. Once the general conditions concerning the lubrication of the compressor and oil type in the plant have been considered, the specific plant conditions must be taken into consideration. Use the Oil recommendation diagrams to select the appropriate oil code number.

The oil code number consists of letters designating the oil type together with the Sabroe viscosity grade number. In the oil recommendation diagrams for each refrigerant and compressor type, it is possible to determine the code number for the oil best suited to the operating conditions. With this code number, it is possible to select the correct Sabroe oil for the application. The marked area on each side of the separating line in the diagram shows the zone where both oils are useable.

Oil types and oil companies

As a result of the large number of oil companies world-wide that deals in oil for refrigeration plants, it is impossible for Sabroe Refrigeration to test the many different brands of oil on the market. It is our experience, however, that some oil brands during use can change character and thus no longer fit the specifications given by the companies at delivery. We have thus experienced changes in the specifications as well as in the formula and performance without having had any information about this from the oil company. This makes it very difficult for Sabroe Refrigeration to give a general approval of the various oil brands.  

For this reason Sabroe Refrigeration has, in cooperation with a large recognised oil company, developed a series of three oils which cover most purposes. Sabroe Refrigeration has however,  also listed a limited number of oils which can be supplied through Sabroe Refrigeration. The typical data of these oils can be found in the Data Sheet for Sabroe Oils. We suggest you to use these Sabroe oils, which are delivered in 20 litre pails and 208 litre drums and can be ordered using the parts no. listed in the List of Oils.

It is of course possible to use similar oils from other oil companies, and in this connection, the Data Sheet for Sabroe Oils may be helpful. Please note, however, that Sabroe Refrigeration has not tested any other oils than our own brand, and hence we cannot answer for the quality, the stability or the suitability of other oils for any purposes.

The oil company in question is thus solely responsible for the quality and suitability of the oil delivered, and if any problems are experienced with these oils in the compressors or in the refrigeration plant, the oil supplier should be contacted directly.When choosing oils from other oil companies, please pay particular attention to the oil's effectiveness in the compressor and the refrigeration plant as a whole. Pay particular attention to the following aspects:

Reciprocating compressors:

Normal oil temp. in the crankcase 50-60 °C

Max. permitted oil temperature = Setting point for alarm

Min. permitted oil temperatures = setting point for alarm - if fitted

Screw compressors: The oil temperature before injection in the compressor, but after the oil cooler

Max. permitted oil temperature = setting point for alarm

Min. permitted oil temperature = setting point for alarm

Reciprocating compressor: Suction pressure and oil temperature in the crankcase.Screw compressor: Discharge pressure and gas temperature.

• Compatibility with the neoprene O-rings: the aniline point gives an indication of how the O-ring material reacts to the oil. At an aniline point less than approximately 100°C the material tends to swell, and at an aniline point higher than approximately 120°C it tends to shrink. For this reason it is not recommended to change oil type from M oil to PAO oil as a leakage may occur if the O-rings are not changed. Sabroe Refrigeration therefore recommends using the Sabroe AP68 oil as it reduces the risk of leaks considerably in this case. Sabroe Refrigeration can supply a calculation showing the operating data on request. Attention is drawn to the following viscosity limits during operation:

Use of mineral oil

Lately we have experienced a number of problems with mineral oil, particularly in R717 plants. The problems can be divided into two groups:

a. The oil changes viscosity within a few operating hours.

b. The oil decomposes (becomes very black) within a few operating hours. The problems have been seen with several oil brands and have resulted in severe consequences

for both compressors and plants. When using mineral oil, it is thus important that the plant is monitored very closely, that oil samples are taken regularly (every 1-2,000 hours) and that the condition/colour of the oil is checked on a weekly basis.

Sabroe Refrigeration therefore recommends only to use M oil at moderate operating conditions - cf. the attached oil recommendation diagrams.

Sabroe Refrigeration is aware, however, that several customers have been using mineral oils for many years without problems. Those customers who wish to continue using mineral oils in existing, as well as new, compressors can do so, providing

the compressor type and operating conditions are similar to the existing ones (excepting the HPC and HPO series compressors). Sabroe Refrigeration has therefore decided to

market a brand of mineral oil which has been tested and found to be suitable for most general refrigerating purposes. If another brand of mineral oil is chosen, the specifications in the data sheet in this recommendation should be followed as a guideline. Mineral oil can be used in refrigerating plants, providing the lubricating quality is carefully monitored. For modern, high capacity refrigeration plants, in which a long lifetime for both lubricant and moving parts is expected, Sabroe Refrigeration recommends using synthetic lubricating oils. A benefit of using the synthetic lubricant oil is a much lower oil carry-over to the plant and longer intervals between oil changes. A better fluidity at lower temperatures also gives an easier drainage at the cold parts of the plant.

How to use the oil recommendation diagrams:

To determine the code number, first refer to the Oil recommendation diagram for the refrigerant and compressor type and then plot the proposed operating conditions.

Example (recip. compressors):

Note: Plants may operate at different conditions from time to time, for example at different evaporating temperatures due to plant variations or at different condensing temperatures due to seasonal changes. By plotting TC and TE in the oil recommendation diagram, this example would require

a No 1 oil. If, however, TE changes at certain times, e.g. from -3 to +7°C, a No 2 oil should be utilised. But, as +7°C is inside the marked area, the No 1 oil can be utilised also at this TE.

 By referring to the Oil recommendation table placed at the bottom of each oil recommendation diagram, it is possible to select the code number for the appropriate oil type. In the example above, a oil code number E5 can be selected. In plants which incorporate both screw and reciprocating compressors and where the recommendations indicate the use of different oil types, please contact Sabroe Refrigeration for advice. 

Changing oil on Sabroe compressors 

The oil should never be changed to another type without consulting the oil supplier. Nor is it advisable to "top up" compressors with an other oil than the one already used for the particular plant and compressor. Mixing different oils may result in operating problems

in the refrigerant plant and damage to the compressors. Incompatibility between the different oil types may degrade the lubricating properties or may cause oil residues to form in the compressor or oil separator or in the plant. These oil residues can block filters and damage the moving parts in the compressor. Furthermore, changing the oil from one type or make to another should only be undertaken in connection with a careful procedure involving the drainage and thorough evacuation of the refrigeration plant. Information on a suitable procedure can be obtained from Sabroe Refrigeration as

well as from a number of oil companies. It is imperative that oil is only used from the original container and that both the make and type complies with the specification for the plant.  Ensure that the original container is sealed during storage to prevent moisture from the air being absorbed into the oil - many oils, particulary the polyolester

oils, are extremely hygroscopic. Consequently, it is recommended that the oil is only purchased in containers corresponding to the amount to be used on each occasion.

If the oil is only partially used, make sure that it is effectively re-sealed in the original container and that it is stored in a warm, dry place. Ideally with nitrogen blanking of the oil to keep the water content below 50 ppm. Oil drums should, ideally, be "racked" and mounted with a proper barrel tap to ensure an effective airtight seal. 

Oil changing intervals

A list of the recommended intervals for changing the oil can be found in the compressor instruction manual. These are provided for guidance only. The actual interval between oil changes will often be determined by a variety of operating parameters within the plant.

It is strongly recommended to monitor the quality of the oil by carrying out oil analyses with regular intervals. This will also give a good indication of the condition of the plant. The service can be supplied by Sabroe Refrigeration or the oil suppliers. Oil recommendation diagram symbols:

Dry expansion systems only. Flooded systems to be considered individually: contact. Sabroe Refrigeration SH Suction gas superheat, K (Kelvin) L Zone in which both oils are useable M Calculation must be performed using COMP1