OCS Cold

Since 1972 pressure vessels for refrigeration and air conditioning systems


OCS COLD carries out continuous research and development in order to offer to its customers the best level of technology according with the innovations required by the market, in particular in the search of new solutions.

Solutions for oil return in refrigeration circuits


RETAX EVO OIL SEPARATOR FOR CAPILLARY TUBE: It is particularly suitable for air conditioning and refrigeration systems where is necessary a continuous oil return and where there are no sudden changes in the refrigerant load as the capillary tube is capable of adapting to the working conditions. The separation of the oil is optimal even in the start-up and reverse cycle phases, usually critical in the separation of the oil. The three stages of filtration optimally manage the separation of the oil even in cases of low or very low flow of refrigerant such as in cases of low or high discharge temperature. This model is designed with an internal dipping tube. During installation a capillary tube must be soldered in its outlet, the section of which must always be less than the diameter of the outlet tube. RETAX for capillary tube does NOT require oil pre-charge.

Solutions for oil return in refrigeration circuits

RETAX EVO guarantees an
oil separation of 99.8%
under all operating conditions

(tests carried out at the Carel Spa laboratories which confirmed the separation percentage)


RETAX EVO OIL SEPARATOR FOR OPTICAL SENSORS: It is suitable for air conditioning and refrigeration systems in which there are rapid variations in the refrigerant load, that is, when the mass flow rate of refrigerant mixed with oil has rapid variations in terms of flow and temperature. With this separator, once accumulated, the oil returns to the compressor in a discharge time of less than 8-10 seconds, guaranteeing the integrity of the cooling performance. This model involves the use of two optical sensors and a reading device for signal processing and requires the installation of a solenoid valve on the oil return line.

Solutions for oil return in refrigeration circuits

Solutions for R744 applications

Solutions for R744 applications
Solutions for R744 applications


The oil separators for transcritical and subcritical systems for applications with R744 refrigerant are available in two versions: HERMETIC or ACCESSIBLE. Equipped with NPT-F connection for mounting the optical level sensor, they can also be supplied (on request) with a service connection. Designed by OCS COLD, both versions guarantee:

  • High coalescence factor achieved by the stainless steel filter mesh
  • Optimal use of the oil separator’s walls in the separation process
  • Elimination of any oil vapors, not yet separated particles, leaking from the attack output
  • Prolonging the life of the compressors thanks to the high oil separation and oil return  to the crankcases in a very short time
  • Excellent filtering capacity of impurities present in the cooling circuit
  • High percentage effectiveness even at high discharge temperatures (up to a maximum limit of 140 ° C at maximum operating pressure of 140bar)




  • Transcritical cascade plant
  • Booster systems
  • Heat pumps
  • Regenerative heat pumps
  • Medium and low temperature refrigeration plants

Solutions for R717 and fluid Group 1 applications

Solutions for R717 and fluid Group 1 applications



The OCS COLD pressure vessels for applications with Group I fluids are designed and produced taking into account the peculiarities of these fluids such as: toxicity and flammability (in the case of R717 refrigerant also the incompatibility with copper and its alloys). The thickness of the shell and tests are therefore specific in order to ensure the safe use of the products. Contact our offices for more information.



Particularly suitable for FLOODED EVAPORATORS and for SCREW COMPRESSORS with or without integrated oil separator, the new cyclonic separator OS_2S BI-STAGE, combines the effectiveness of cyclonic motion and the patented RETAX system in a single combined action so as to ensure extremely high performance reliability (separation of oil from refrigerant by 99.8%) in any operating condition. The functionality of the evaporators is thus preserved from any malfunctions due to the presence of oil foam. The return of the oil to the compressors is thus ensured by the almost total separation of the oil, ensuring functionality and consequently lengthening the life span of the compressors themselves. The OS_2S BI-STAGE oil separators can be supplied with or without integrated oil reserve according the construction requirements of the refrigeration machine. In addition to the standard models, OCS COLD can produce customized models that adapt to the most varied technological needs.

The oil separation occurs in two stages of filtration:

  1. "Refrigerant + oil" flow such as to also exploit the effect of the separator wall
  2. Filtration capacity of the microparticles up to a minimum value of 3 microns.

The oil separation process takes place through 2 filtering stages:


The separation of the oil takes place thanks to the cyclonic motion of the mixed refrigerant with oil. Thanks to the centrifugal motion of the refrigerant in the cyclone section of the separator and the internal tube, the oil begins to separate in large quantities. The speed of the refrigerant inside the cyclone section is calculated  in order to obtain an exact combination between the tangential motion and the ideal speed for the separation of the oil.


When the refrigerant reaches the 2nd stage of filtration, much of the oil has already been separated from the cyclone section of the 1st stage. At this point, the refrigerant, mixed with a very small quantity of oil, similar to a mist, passes through the internal 3-stage RETAX filter, which thanks to the coalescence phenomenon further filters the residual oil particles, reducing and uniforming the coolant flow.

The three stages of Retax filtration:

(Results guaranteed by numerous tests carried out at Carel Spa Laboratories, which, after a long series of experimental tests, have certified the percentage of separation)    

  1. The refrigerant gas mixed with the oil enters a flow distributor tube. This tube, thanks to its calibrated holes, distributes the fluids uniformly towards the following filtering sections. The oil begins to separate further already inside the tube thanks to the rapid change in direction of the residual refrigerant / oil mixture.
  2. At this point the mixture passes through the first stainless steel filter, on which the oil begins to thicken, forming a large quantity of medium and large drops. The flow speed remains at optimized values, promoting the effectiveness of the coalescence process.
  3.  In the 3rd filtering phase, the metal mesh filter allows you to thicken the remaining particles and oil vapors, ensuring an overall separation of 99.8% of the oil from the refrigerant.

The two stages of filtration offered by the cyclonic separator OS_2S allow an almost total separation of the oil thanks to the combination of the separation of the cyclone with the very high efficiency filtration characteristics of the 3-stage RETAX filter. Oil separation remains efficient even with high mass flow rates and high evaporation and discharge temperatures (T disch.> 110 °C). Separator efficiency certified at 99.8% detected by technical and experimental tests.

Ability to resist any type of wear

Minimum pressure drops

Filtration of any impurities in the cooling circuit without decreasing its efficiency



Suitable for any type of application, in high or low temperature, for HCFC - HFC - HFO refrigerants as well as with R717 natural refrigerant;
Separator efficiency certified at 99.8% detected by technical tests and experimental checks;
Filtration with centrifugal process at the 1st cyclonic stage;
2nd stage filtration carried out in 3 successive steps;
Drastic reduction of pressure drops at the 2nd stage filter;
Longer life of the compressors, because the oil returns to the compressors almost immediately;
Maintenance interventions related to compressors can therefore also be reduced.
Suitable for refrigerant fluids such as:
HCFC - HFC - HFO (R134a, R513A, 1234yf, 1234ze, R507A, R404A, R448A, R449A, R450A, R402A, R427A) and R717
The cyclone separators are equipped with flanged connections for input / output, NPT-F connections for level sensors, sight glass  for oil level monitoring , oil heaters, and accessories for the safety of the refrigeration system.
The OS_2S BI-STADIO oil separators are CE marked and designed and produced according to Directive 2014/68 / EU).

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