The operation of all alarms and shutoffs utilize components which are actuated by a sensing unit. The alarms and shutoffs are set at critical operating temperatures, pressures, or speeds in order to protect the engine from damage.
Alarms function in order to warn the operator when an abnormal operating condition occurs. Shutoffs function in order to shut down the engine when a more critical abnormal operating condition occurs. The shutoffs help to prevent damage to the equipment.
If an engine protective device shuts off the engine, always determine the cause of the shutoff. Make the necessary repairs before attempting to start the engine.
Shutoffs may cause unburned gas to remain in the air inlet and in the exhaust manifold.
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Unburned gas in the air inlet and exhaust system may ignite when the engine is started. Personal injury and/or property damage may result. Before starting an engine that may contain unburned gas, purge the unburned gas from the air inlet and exhaust system. Refer to the topic on purging unburned gas in the "Starting the Engine" section. |
Become familiar with the following information:
- Types of the alarm and shutoff controls
- Locations of the alarm and shutoff controls
- Conditions which cause each control to function
- Resetting procedure that is required before starting the engine
On CG137-12 Engines, protective devices are available for the following conditions:
- Low oil pressure
- High coolant temperature
- Overspeed
- Low coolant level
Further protection is supplied by an emergency stop button.
Three basic protection systems are available:
- Self-powered shutoff
- Automatic start/stop system
- Customer supplied shutoff
Note: For an energize-to-shutoff system, the gas shutoff valve must be energized to shut off gas to the engine. For an energize-to-run system, the gas shutoff valve must be energized in order to supply gas to the engine.
Power for the self-powered system is supplied by the magneto. The self-powered system can be used with an air starting motor or an electric starting motor. An energize-to-shutoff gas valve and an instrument panel are required for this system.
Power for the automatic start/stop system is supplied by an external 24 V electrical source. The automatic start/stop system can be used with an air starting motor or an electric starting motor. An energize-to-run gas valve and one of these controls are required:
- Automatic start/stop switchgear
- Engine Control Logic
For the customer supplied shutoff system, the customer must supply all of the wiring and the shutoffs. The customer supplied shutoffs and wiring includes the emergency stop button and wiring.
The features of the shutoff systems are listed in Table 1.
| CG137-12 Engine Protective Systems | |||
| Item | Type of System | ||
| Self-Powered | Automatic Start/Stop | Customer Supplied (1) | |
| High coolant temperature | Yes | Yes | Yes |
| Low oil pressure | Yes | Yes | Yes |
| Overspeed | No (2) | Yes | Yes |
| High inlet manifold air temperature | No | No | Yes (3) |
| High aftercooler water temperature | No | No | Yes (3) |
| Emergency stop | Yes | Yes | Yes |
| (1) | The customer is responsible for supplying the shutoffs and the wiring. |
| (2) | Overspeed protection is available as an option. |
| (3) | The customer is responsible for supplying the protection for either high inlet manifold temperature or high aftercooler water temperature. |
The sensing devices that are described in this section are typical. The devices may be in different locations for different applications. Also, different applications may have different devices.
Engines that use different generator set control panels will have different sensing devices.
Speed sensor helps to monitor the engine rpm. The speed sensor senses the motion of the flywheel ring gear. The speed sensor is used with a tachometer in order to display the engine rpm.
The speed sensor can also be used with an electrical overspeed switch.
The overspeed switch is mounted in the junction box. The recommended setpoint is 110 percent of the rated rpm. If an overspeed occurs, the "RESET" button on the switch must be reset before the engine can be started.
The switch also has a "VERIFY" button. The button enables the operation of the switch to be tested at 75 percent of the rated rpm.
Overspeed contactor can be installed behind the magneto on the tachometer drive. The overspeed contactor is a mechanical device. Excessive engine rpm activates the contactor with centrifugal force.
Air temperature switch for the aftercooler is installed in the housing of the aftercooler. The shutoff is supplied by the customer.
Coolant temperature switch is located next to the housing for the water temperature regulator. An excessive water temperature will activate a shutdown. The setpoint that is recommended for a high coolant temperature shutdown is
Oil lines for sending oil pressure can be located in various places on the side of the engine block. The oil lines are connected to the bearing oil gallery. The oil lines can be connected to these different components:
- Instrument panel
- Junction box
- Oil pressure switch
Low oil pressure will activate a shutoff. The recommended setpoint for low oil pressure is
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| Illustration 1 | g00788388 |
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Coolant loss sensor | |
The coolant loss sensor is an optional feature. The sensor is mounted near the top of the radiator. A lack of sufficient coolant can activate an alarm or a shutoff. Coolant must be added to the cooling system in order to correct the condition.