The arrangement is as shown in figure.
- Lubricating oil is pumped from the sump via a filter to a 3-way valve fitted in the line.
- This valve is controlled by a temperature sensor located at the inlet to the main engine.
- The valve is designed to fail safe, ensuring that in case of failure, all oil passes through the cooler before entering the engine.
- The sensor at the engine inlet continuously monitors the oil temperature and transmits the signal via a transmitter to the controller.
- The controller receives the measured value and compares it with the pre-set value.
- Based on the comparison, the controller sends an output signal to the pneumatic control valve.
- The valve then regulates the oil flow: part through the cooler and part bypassing it, so that the final temperature of oil entering the engine is maintained within safe limits.
If dust or water is present in control air, it may cause the following problems:
- Blockage of orifices.
- Blockage of nozzles.
- Clogging of dryers.
- Formation of deposits inside pipelines.
- Corrosion of system components.
- Pressure drop within the system.
- Freezing in the lines, which may block actuators and mechanisms.
Hence, control air must be maintained free from dust and water.
- By providing separate control air dryers onboard, commonly of the refrigeration type, which condense moisture and drain it off.
- By using adsorption dryers (e.g., silica gel, activated alumina).
- By fitting automatic drains on air filters to remove water.
- By using auto-unloaders on air compressors to discharge accumulated condensate.
If control air contains contaminants (particles above 5 microns):
- Blockage of orifices.
- Blockage of nozzles.
- Damage to diaphragms.
- Damage to O-rings.
- Corrosion of pipelines.
- Overall pressure drop in the system.