Introduction
Read the instructions in this manual before the assembly, the commissioning procedure, the maintenance, and the repair of the oil mist detector. Failure to follow the instructions may void the manufacturer's warranty. The instructions in this manual are applicable to the systems that include the following oil mist detectors:
Excessive Oil Mist
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An excessive concentration of oil mist in the crankcase can result in an explosion. An explosion in the crankcase will cause catastrophic damage to the engine which can also result in serious personal injury or death. To help prevent an explosion, the oil mist detector must be installed, maintained, and repaired according to the instructions in this manual. |
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An explosion in the crankcase is the result of a series of events which cause a high concentration of oil mist to form rapidly in the crankcase. The following steps explain the cycle.
- A root cause occurs. This can occur long before the actual failure begins. The following examples are conditions of root causes of failures:
- Contaminated engine oil
- Engine overspeed
- Excessive service hours
- Contaminated engine oil
- As a result of the root cause, a component begins to fail. The following examples are conditions that will eventually cause component failure:
- A particle is embedded in a bearing.
- Crankcase blowby is increased.
- The bolts of a connecting rod are stretched.
- A particle is embedded in a bearing.
- Additional damage is caused by the component failure. The following conditions are examples of component failure:
- A hot spot is formed in a bearing.
- Some components develop an unbalanced load.
- A hot spot is formed in a bearing.
- The component failure eventually causes extreme temperatures which vaporize the lubricating oil.
- When the vaporized oil condenses in the crankcase, oil mist is formed. If the concentration of oil mist continues to increase, an explosive level is eventually reached.
Note: Oil mist is not smoke. Oil mist consists of fine droplets of oil that are suspended in the atmosphere of the crankcase. The droplets vary in sizes of approximately one to ten microns.
Detection of the problem prior to the failure of a component may not be possible. The monitoring of parameters such as bearing temperatures can reveal the development of component damage. This type of damage is detected over time by a gradual increase of the temperature.
Most component failures that cause excessive oil mist are not detected until damage to components is causing the concentration of oil mist to increase. An explosive level of oil mist can form within a few seconds. To minimize potential damage, the oil mist detector must be installed, maintained, and repaired according to the instructions in this manual.
Product Description
The oil mist detector helps protect the engine against serious damage that can originate from the overheating of bearings and/or piston components.
The 191-6505 Oil Mist Detector is used in crankcases that do not have separate compartments. The atmosphere from the crankcase is drawn through two manifolds that sample the atmosphere of the entire crankcase. In this type of crankcase, it is possible for the oil mist to spread rapidly throughout the crankcase. If the oil mist exceeds the threshold, the alarm relay is activated. This detector does not determine the location for the alarm.
The 149-5143 Oil Mist Detector is used in crankcases that have separate compartments. The atmosphere from the crankcase is drawn through individual pipes that sample the atmosphere from each compartment. The detector can use a maximum of ten pipes. If the oil mist exceeds the threshold, the alarm relay is activated. The detector then determines the source of the oil mist. Valves for all of the pipes are sequentially opened and closed in order to sample the atmosphere from each compartment. Groups of compartments are compared. The compartment with the alarm is indicated on the face of the detector.
Illustration 1 shows the main components of the detectors.
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| Illustration 1 | g00730467 |
(A) 191-6505 Oil Mist Detector (B) 149-5143 Oil Mist Detector (1) Inspection cover of the measuring head (2) Display (3) Connection for the atmosphere from the crankcase (4) Base plate and vacuum (5) Plug for the main power supply | |
The detector has a ready relay which is activated when the green "READY" LED is illuminated. This indicates that the detector is in good working condition.
The atmosphere from the crankcase is continuously drawn to the detector through manifolds or pipes that have sampling ports in the crankcase. The atmosphere in any crankcase will have large droplets of oil that are not associated with oil mist. The large droplets of oil are separated from the atmosphere by a separator that is in the base plate of the detector. This oil is routed out of the detector through an oil drain. For some engines, the oil is drained into a box for disposal. For other engines, the oil is routed back to the crankcase.
The atmosphere is passed through a measuring track in the detector. The measuring track has a diode that emits infrared light through the atmosphere to a diode that receives the light. The diode that receives the light converts the intensity of the light into an electronic signal. The signal is evaluated by an electronic module.
The amount of light that is absorbed by the atmosphere is directly proportional to the amount of oil mist in the atmosphere. An excessive amount of oil mist reduces the amount of light that is received by the diode. This reduces the strength of the signal that is evaluated by the electronic module. If the signal is less than the threshold value, the module evaluates the signal as excessive oil mist. The module activates two alarm relays. One relay is for the alarm and the other relay is available for a customer connection.
If an alarm occurs, the alarm relays are activated and a red "Alarm" indicator on the detector flashes. The captain and/or the chief engineer of the vessel is responsible for the response to an alarm. This can include derating (a reduction of power) and/or shutdown.
Note: For wiring of the alarm relays, see the schematic of the engine electrical system. If the engine is equipped with the Caterpillar Marine Monitoring System, also see Owner's Manual, SEBU7134, "3600 Diesel Marine Monitoring System". If the engine is equipped with the Caterpillar Marine Monitoring System II, also see Service Manual, RENR2490, "3600 Diesel Marine Monitoring System".
If an alarm occurs, the alarm is stored in the detector until the "RESET" button is pressed. Fault information is also cleared with the "RESET" button.
The detector is capable of self-diagnosis. If the detector senses a system fault, the ready relay is deactivated and the green "READY" lamp is extinguished. Under these circumstances, the detector cannot activate an alarm for excessive oil mist.
If a fault occurs, the fault is stored in the detector until the "RESET" button is pressed. When the "RESET" button is pressed, all of the fault information is cleared.
Condensation of water in the measuring track can activate a false alarm. Condensation can especially be a problem in environments that have high humidity. The detector has a heater in the measuring head that warms the atmosphere from the crankcase in order to help control condensation. This helps avoid false alarms from the condensation.
To avoid fouling of the infrared filters, filtered air is continuously drawn into two chambers that are between the infrared filters and the atmosphere from the crankcase. This helps prevent any oil that is contained in the atmosphere from contaminating the glass of the infrared filters.
If the ambient air is drawn into the detector, the presence of pollution and/or smoke in the engine room could activate a false alarm. To help avoid this situation, compressed air is supplied to the air chambers. This air is independent of the ambient air in the engine room.
The filtered air is provided to the detector through a pressure regulator that also has a limiter. If the regulator has a failure such as a ruptured diaphragm, the maximum pressure is limited to 25 percent more than the calibrated pressure.
Opacity - This characteristic obscures the passage of light.
Provisions are made for reducing the contamination of the infrared filters. However, the filters get dirty. This is interpreted by the detector as an increase of opacity. The service hours of the equipment can also be interpreted as an increase of opacity. Also, different temperatures can have an effect on the electronic system. Unlike a sudden excessive oil mist, these effects occur over time. The effects are not confused with a rapid alarm condition.
To remedy the influence of these effects, the detector calculates a value of reference for opacity when voltage is supplied to the detector. The calculation accounts for the condition of the infrared filters, etc. The value of the reference reflects the opacity that exists when the detector is powered up.
The oil mist detector has an internal switch for increasing or decreasing the optical sensitivity. The position is not normally changed. Consult Caterpillar, Inc. before you make any adjustments.
Contact with the oil mist detector is only required for the following circumstances:
- Maintenance
- An occurrence of an alarm for oil mist
- A fault condition is activated by the oil mist detector.
For the maintenance schedule and maintenance procedures, see this Systems Operation, "Maintenance Schedule".
For instructions on the occurrence of an alarm and/or malfunctions, see the Testing and Adjusting, "Troubleshooting".
| Technical Data | |
| Vacuum in the measuring track | 70 ± 10 mm of H2O (2.8 ± 0.4 inches of H2O) |
| Vacuum pump | 0.3 to 0.5 bar |
| Air consumption | Dependent upon the number of sampling ports Maximum of 1 m3 per hour |
| Permissible operating temperature | 0 to 70 °C (32 to 158 °F) |
| Permissible temperature of the oil mist | 70 °C (158 °F) maximum |
| Permissible temperature for storage and transport | -25 to 80 °C (-13 to 176 °F) |
| Maximum relative humidity | 90 % |
| Maximum vibration | 6 g of acceleration |
| Weight of the 191-6505 Oil Mist Detector | 7.5 kg (16.54 lb) |
| Weight of the 149-5143 Oil Mist Detector | 9.6 kg (21.16 lb) |