The newly developed VISATRON® series VN87plus Oil Mist Detector (OMD) from SCHALLER AUTOMATION protects large diesel engines against oil mist explosion, caused by spontaneously occurring oil mist. It is part of a safety system that secures the life and health of the operating staff and prevents heavy damages to the engine.
SCHALLER AUTOMATION developed this device to meet the IACS UR M10.
It is not possible to directly monitor all potential sources of oil mist inside a large diesel engine. There are main bearings, large end bearings, pistons, liners, sliders, pumps, camshaft bearings, chains, gears or even tools left behind from installation - all of these parts could produce oil mist e.g. in case of lubrication problems. Therefore the philosophy of SCHALLER AUTOMATION is that only OMD-systems can securely prevent oil mist explosions by detecting the primary origin of danger: the oil mist itself.
The VISATRON® series VN87plus OMD-system uses the approved wear-free suction system to continuously extract the atmosphere of the crankcase compartments and other engine locations. The system works actively and is not simply waiting for oil mist clouds. This ensures proper reaction times from the beginning of oil mist generation to an oil mist alarm.
To avoid false alarms caused by splash oil the suction system makes use of Schaller's special suction funnels working independent of the rotation sense of the engine. Additional draining components ensure correct working under all operating conditions. This includes the application in power plants as well as on vessels with their static or dynamic inclinations. False alarms initiated by condensing water vapour are prevented by an integrated heater inside the measuring head housing.
The OMD-system consists of following parts:
- * VISATRON® series VN87plus oil mist detector
- * Protection cover
- * Suction system including pressure regulator
- * Monitoring device (optional)
- * Protection cover
Three different types of the VISATRON® series VN87plus oil mist detectors are available (see Figure 1):
- * VN115/87plus
- * VN116/87plus
- * VN215/87plus
- * VN116/87plus
All devices have a measuring head (2) which includes the optical measuring track under the control cover (3), a label on the front side and a display to give the user all important information for normal operations conditions. The measuring head is mounted on a vibration protected base plate.
- The negative pressure for the suction system is generated by an air jet pump (1) working with the Venturi principle. The electrical interface is integrated within a socket housing (5). The mating plug contains the Oil-Mist-Alarm button. The device can be connected directly to the engine safety system. The interface includes two Oil-Mist-Alarm outputs, a Pre-Alarm output and a Ready signal.
VN115/87plus
The suction system is connected to the common "Connecting Box" (4). This type of oil mist detector is able to detect an oil mist development, without identifying the location of the oil mist source inside the engine.
VN116/87plus
The suction system is connected to the "Valve Box 116" (4). This type of oil mist detector is able to detect an oil mist development, indicating in the valve box window the left or right side of the detector with the highest oil mist concentration.
VN215/87plus
The suction system is connected to the "Valve Box 215" (6). This type of oil mist detector is able to detect an oil mist development, indicating in the valve box window the compartment with the highest oil mist concentration.
In normal operation mode all models sample the atmosphere of the engine at all suction points in parallel through the suction system to the measuring head. Upon detection of an oil mist alarm the models VN116 and VN215 start an additional search run to determine the location of the highest oil mist concentration. The reaction time to an alarm is totally independent of the search run.
All devices offer two alarm levels. The Main-Alarm level can be adjusted with a switch at the rear side of the measuring head. The Pre-Alarm will we activated at fix 70% of the Main-Alarm level.
To keep the optical track clean all models use clean scavenging air in front of the filter glasses. This air is derived from the compressed air driving the air jet pump.
The devices can be ordered as single OMD device or integrated in a mounting unit. In this case the scope of supply includes an additional pressure reducer and a protection cover.
The suction system always requires a so called 'suction funnel' (see page 21, Fig. 19) at each suction point. This prevents the system against incoming splash oil. During normal operation mode of an engine the OMD sucks out a small concentration of oil mist which was generated by blow-by or mechanical spraying. This oil mist may fall out in the suction pipes and must be drained out the pipes. Ideally, drainage flow back ends inside the engine's crankcase.
The best method on a VN115/87plus and VN116/87plus installation to drain the system is to use pipe siphons. Also recommended is the use of siphon blocks.
On 2-stroke engines the crankcase and the combustion chambers are separated by stuffing boxes, which let the crankcase be nearly free of blow-by. Therefore it's also possible to use the suction funnel as draining device. In this case it is necessary to mount the suction pipes with an inclination of greater than 6°.
To become independent from fast changes of the engine room air pressure, it is recommended that the output of the air jet pump is blown back into the crankcase. If the air is blown into the engine room, SCHALLER AUTOMATION offers an optional oil separator which should be mounted directly to the output of the pump.
Remote monitoring devices:
The OMD device can be connected to Schaller's monitoring devices Remote Indicator II or ReCon DS23 to monitor the oil mist concentration and the status of the OMD device from a safe location as requested by IACS UR M10. The connection to the monitoring devices is realized by a RS485 two-wire bus.
Additionally Schaller realized an integration of the VISATRON® devices into ship automation systems (e.g. Mega-Guard of Praxis Automation).
Thus, the series VN87plus is a further contribution to safety at sea. Our goal is to avert damage to assets, personnel and the environment.
Important features of the series VN87plus compared to the series VN87
- * Heater is integrated into the measuring head, no external connector
- * Scavenging air is integrated into the measuring head, connecting hose same as supplied before
- * Pre-alarm interface available, threshold is fixed to 70% of main-alarm level
- * Serial interface for monitoring devices is integrated
- * Additional error codes
- * Switch for the adjustment of the main-alarm level is placed on the rear side of the measuring head, no disassembly of the electronic module furthermore necessary
- * Switch for the adjustment of the bus device address is available on the rear side
- * Easier access to the wire break resistors on the rear side
- * Optional 4 -20 mA output of the relative opacity data
- * Scavenging air is integrated into the measuring head, connecting hose same as supplied before
