WOR - automatic oil return
In order to guarantee an automatic oil return to the compressors, there are several components required:
  • a device that will return the settled oil respectively the refrigerant/oil mixture to the compressor (BDP /BDP2)
  • a corresponding control for the return (time control or with BDP2 optionally a sensor)
  • a heat exchanger (DWR) which ensures that the refrigerant will be evaporated our of the oil
  • an oil fine filter (ÖF)
  • a sight glass for the observation of the oil return
control of the automatic oil return

There has to be a command that demands when and how long the solenoid valve in the control line should be opened. The decision how this is established should be made by the project engineer.


time control
The simplest method is to open the solenoid valve x-times a day for approximately 2-3 minutes. The execution of this time control should be done by the manufacturer of the control cabinet.

demand control with the WITT-sensor
By means of a sensor you can check if the BDP2 is filled with refrigerant or with oil.

bdp2_motiv.jpg WITT BDP2
represents the consequent improvement of the well established WITT BDP for automatic oil return in refrigerant systems. The internal function unit as well as the check valve in the outlet connection were optimised.

The advantages for you:
  • Maintenance-free
  • Internal damping allows use of hot gas at high pressure
  • G1/4" connection, e.g. for measurement of the oil level
  • Easy installation
  • Flexible positioning of connections
  • G1" fill connection of proven BDP
  • Less sensitive towards contamination
  • Possibility to disassemble the BDP2 for cleaning or adoption to changing system requirements
  • Design pressure of 40 bar

Flow heat exchanger DWR
The flow heat exchanger DWR is used as a component of the WITT oil return system WOR. It serves to protect the compressor from liquid beats.

The fluid that is pushed out of the BDP/BDP2 belongs to the WOR system may be pure oil or an oil/refrigerant mixture, which can not be predicted. In any case, the use of a heat exchanger to evaporate possible refrigerants and to protect the compressor units is required.
To avoid liquid refrigerant may enter the surge line to the compressor any residue liquid refrigerant that may be left in the oil/refrigerant mixture is evaporated by the flow heat exchanger DWR. For this purpose hot gas from the compressor is used freely and directed through the inner tubes.
On the way through the shell area, the refrigerant is completely evaporated. The best efficiency is achieved with vertical mounting.
The DWR must be installed in a position that the BDP2 inlet is from bottom of the DWR.
The DWR series from DN32 to DN200 with a pressure nominal PN25 or DWR80 with a pressure nominal PN40 is in stock available at TH.WITT.
Oil fine filter type ÖF
oef.jpg Oil fine filter type ÖF

The installation of an oil fine filter in the oil return system can make sense as a precaution. For this purpose there is the type ÖF-G1/4“. The oil fine filter is mounted behind the heat exchanger DWR in the return line to the compressors.
HDB - oil drain vessel
hdb2e.gif The WITT - HDB oil drain vessel collects any insoluble oil that has settled. The HDB is placed at the lowest spot of the surge drum whereby the connection must align with the surge drum shell.
(Under no circumstances the connection should extend into the vessel!).

To drain any oil the stop valves to the HDB should be closed. Due to heat intake from the environment the pressure within the HDB  vessel increases and allows that oil to be drained through a combination of WITT stop valve EA 10 GB and a WITT quick acting valve SSV 6 . In order to accelerate this process a heating element can be added or hot gas may be applied. Upon oil-drainage the drain valves should be closed and the stop valves to the HDB vessel re-opened.

For further information about design, installation or operation please see our instruction manual.

Accessories (optional)
- WITT quick acting valve SSV 6
- heating element
- brackets