G342C NATURAL GAS ENGINE Caterpillar

Governor Controls

Various types of governor controls can be installed on engines according to the application. The most common control is direct mechanical. The control may be mounted either on the engine or on a remote control panel. Engine mounted controls normally consist of a positive locking handle connected directly to the governor shaft. Cables and vernier controls mount on the engine or on a control panel.

Shutdown controls are used only to stop the engine. Mechanical or electrical controls are commonly used. These devices stop the gas flow. Shutdown controls allow the engine to be restarted after shutdown without readjusting the speed controls. Shutdown controls are usually found on Automatic Start-Stop installations.

Gauges

OIL PRESSURE

WATER TEMPERATURE

Gauges provide a "look" inside the engine. Be sure they are in good working order. You can determine what is "normal" operating range by observing the gauges over a period of time. The cause of any sudden or significant change in the readings should be determined and corrected.

OIL PRESSURE - Oil pressure is normally greatest when starting a cold engine. As the oil warms up it will produce less pressure. Oil pressure is greater at operating speeds than at low idle. Fluctuating readings can mean air in the oil or a sticking pressure relief valve. Stop the engine immediately if a sudden loss of oil pressure occurs.

WATER TEMPERATURE - The operating temperature is determined by the water temperature regulator. High coolant temperatures mean the cooling system is not dissipating enough engine heat. Pressurized cooling system gauges are marked with ranges rather than temperatures. If the gauge indicates in the red range, the cooling system should be inspected.

The minimum operating temperature should not be below the opening temperature of the water temperature regulator.

In cold weather the temperature gauge may fluctuate in or near the cold range. This indicates the engine is being overcooled. In these instances the use of radiator louvers is suggested.

AMMETER

AMMETER - The ammeter should register in the charging range when the engine is running above low idle. If the gauge registers a discharge when the engine speed is increased, determine the cause.

Automatic Start-Stop

An automatic start-stop system ensures that power is supplied to a load when the normal power source is interrupted. The cranking panel is the heart of the system and consists of the failure warning system and relays to start and stop the engine. When a power failure occurs the system senses the failure and starts the engine to transfer the load to standby. When power is restored, it senses and transfers the load from standby and stops the engine. The major use of automatic start-stop systems is standby electric sets and this discussion is limited to that application.

If a power failure occurs, a circuit breaker opens and a set of contacts in the transfer switch closes, completing the circuit to the starter motor. When the engine starts, the starter circuit opens, protecting the starter from overspeed damage.

Since a standby engine is usually unmanned, it is usually protected from mechanical malfunction by a series of electrical safety devices: high water temperature, low oil pressure and engine overspeed. If a fault occurs it energizes one of the shut-off controls and grounds the magneto to stop the engine.

If the unit has a standard cranking panel, the battery and starter are protected from prolonged cranking by a cranking cycle timer. A timer providing five ten-second cranking cycles can be used. Both units have fault lights which light if the cranking cycle is completed and the engine does not start.

Automatic start-stop units may have a time delay relay to prevent the standby circuit breaker from closing until the engine has had a few seconds warm up time. A shutdown time delay provides up to two minutes to cool off after the load has been transferred back to normal power source.

A time delay relay in the transfer circuit can be adjusted from 1 to 30 minutes. This delays the transfer from standby to normal power until the normal source has been restored and remained stable for the preset period.

Unattended units may have an exerciser. At a preset time the engine automatically starts and runs, under load if possible, and shuts itself off. This helps to ensure the until will start and perform as required when necessary.

A shutdown timer may also be used with an automatic start-stop system. This provides a two minute cool off period after the load has been removed from the engine. This allows the heat of full load operation to be dissipated gradually.

Many safety circuits have fault lights to aid the operator in locating the cause of the malfunction. These lights are lighted by the safety circuit that is energized by a mechanical fault i.e., high water temperature, low oil pressure, etc.

Safety Gauges

Safety shut-offs protect the engine from damage if conditions exceed normal operating limits. The safety circuits sense oil pressure and water temperature. The sending units are a part of the gauges in the instrument panels. If a fault occurs, the water temperature or oil pressure indicator will make contact with a terminal and completes the shutdown circuit. A magnetic switch is energized and grounds the magneto to stop the engine. Before restarting the engine, push the magnetic switch reset button, located on the instrument panel. The oil pressure switch reset button, located on the oil pressure gauge, must be held in during starting.

SAFETY GAUGES

A manual stop button located on the instrument panel should be used only in an emergency. The manual stop button grounds the magneto to stop the engine.

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Unburned gas left in the manifold can ignite when the engine is restarted.

Before restarting any gas engine which was stopped by grounding the magneto, crank the engine with the gas valve turned off and the magneto grounded for 10-15 seconds. This will clear the unburned gas from the exhaust system.

Gas Shut-Off Valve

A gas shut-off valve is available. On an electrical signal from either the safety circuit or a remote mounted switch, the valve closes, stopping the gas flow to the engine. This valve must be reset manually.

Overspeed Switch

A contractor actuated by a flyweight governor provides overspeed protection for the engine. The overspeed switch is mounted on the tachometer drive. If the engine overspeeds, the governor closes the contacts, energizing the magnetic switch. The switch grounds the magneto to stop the engine. When an overspeed occurs, the switch must be reset before the engine can be started.

RESET OVERSPEED SWITCH

Safety Shut-Off

A safety shut-off system which is not part of the gauges is available. The system stops the engine if the oil pressure or water temperature exceed safe operating limits. The overspeed switch can be used with this system.

High water temperature causes an internal element to expand and operate a microswitch. The microswitch closes and grounds the magneto, stopping the engine. The magneto is grounded by contacts in the oil pressure switch if oil pressure falls below safe operating limits. A magnetic switch, used with the safety gauges, is not required with this safety shut-off due to higher capacity contactors.

NOTE: Oil pressure shut-off is designed to protect engine from sudden oil lossage or pressure, not against low oil level. Likewise, the temperature shut-off protects against an increasing water temperature but offers no protection against sudden water lossage or when temperature element is not in the water. A low coolant level will not actuate the switch.

After an emergency shutdown, the oil pressure and/or overspeed switch must be reset.

The oil pressure switch must always be reset before starting the engine. To reset the switch, push the button to the OFF position. As oil pressure increases the button will automatically position itself to the RUN position.

Safety Shut-Off Testing

Safety shut-offs function only when an abnormal condition exists. Because the shut-offs operate only in time of a mechanical emergency, it is impossible to tell if they are in good working order through normal operation. Since it is important they are in working order, have the shut-offs checked periodically by your Caterpillar dealer. See the Lubrication and Maintenance Chart for service intervals.

Alarm Switch

Alarm switches are available to notify the operator that a fault condition exists. If oil pressure drops to a dangerous level or water temperature reaches a high level an alarm is activated. Depending on the system, a light is turned on, or a bell or horn is sounded calling the operator's attention to the problem.