Some lubricated objects (like fast moving, heavy loaded bearings or bearings with the need of heat transfer, or gear boxes) are often lubricated by a circulation system. The system consists of a pump unit with tank, filter and cooler, a pipe system and a flow meter for each lubrication point. The system is usually controlled by a separate controlling unit, but can also be controlled via the machine’s PLC. Each lubrication point has not only an inlet but also a return

line which enables for the oil to pass the bearing or gear box. A constant pressure is being sustained in the pipe line between the tank and the flow meter. The pressure drop over the flow meters is then constant as well, which is necessary to maintain a regular and smooth flow to each bearing. The pump works continuously. The return oil from the bearings has absorbed contaminations, heat, and perhaps moist. It is therefore filtered and cooled down. It can also be