D330, D333, 3304, 3306 – Safety Devices

Water Temperature Contactor Switch
A water temperature sending unit is located in the water temperature regulator housing. The unit is nonadjustable. Thermal expansion of the element operates a micro-switch that signals the shutoff solenoid which causes engine shutdown. If overheating occurs due to low coolant level or no coolant, the sending unit will not function. The water temperature element must be in contact with the coolant.

The water temperature sending unit can also be wired into an alarm system or light to signal high water temperature. After an overheated engine is allowed to cool, the contactor automatically resets itself.


Shutoff Solenoid
The rack shutoff solenoid, when energized, moves the shutoff lever in the governor housing which in turn moves the fuel rack to the shutoff position. The solenoid can be energized by any one of several sources. The most usual are: water temperature contactor switch, oil pressure contactor switch, overspeed contactor switch and remote manual control switch.


Overspeed Contactor Switch
An overspeed contactor, which is actuated by high engine speed, protects the engine from damage due to overspeeding. The overspeed switch is mounted on the tachometer drive. If the engine overspeeds, the switch contacts close and signal the shutoff solenoid to shut down the engine. When the engine shuts down because of overspeeding, the overspeed contactor switch must be reset by pushing reset button (1).

1. Reset button.

Pressure Switch
A fuel pressure switch, in automatic start-stop systems, is in the circuit to keep the rack solenoid from staying energized after shutdown. The switch opens the circuit when fuel pressure falls after the engine has stopped. This switch is located at the fuel filter.

A second similar pressure switch is in the battery charging circuit to open the circuit between the alternator regulator and charging alternator when oil pressure lowers after the engine has stopped. This switch is located on the left side of the engine near the flywheel housing.


Oil Pressure Contactor Switch
An oil pressure contactor protects the engine from damage due to low oil pressure. When oil pressure drops below the established limits, one set of contacts close thus signaling the shutoff solenoid to shut down the engine. A second set of contacts, on automatic start-stop applications, opens to disconnect the starter solenoid or magnetic switch when engine is running with normal oil pressure.

The oil pressure contactor switch can also be wired into an alarm system or light to signal low oil pressure.

Micro Switch Type
As pressure in bellows (6) increases, arm (4) is moved against tension of spring (3). When projection (10) of arm (4) touches arm (9), pressure in the bellows moves both arms and in turn moves micro switch button (8) to activate the switch contacts.

Where the switch is equipped with a set-for-start button, manual control of the switch contacts is accomplished by pushing in the button.

1. Locknut. 2. Adjusting screw. 3. Spring. 4. Arm. 5. Spring. 6. Bellows. 7. Latch plate. 8. Micro Switch button. 9. Arm. 10. Arm projection.

Latch plate (7) holds arm (9) against micro switch button (8). When pressure moves arm (4) so arm contacts latch plate (7), the set-for-start button is released and returned to the out position by spring (5).

Earlier Type Switch
Oil pressure contactor switch with control knob (1) must be reset every time the engine is stopped. Turn the knob (1) counterclockwise to the OFF position. The knob moves to the RUN position when normal oil pressure is sensed.

1. Control knob.

Oil Pressure-Water Temperature Shutoff
This oil pressure shutoff is mounted on the hydra-mechanical governor cover. The spring (2) is compressed, when starting the engine, by moving lever (1) against spring pressure. As oil pressure increases, it moves piston (3) to hold spring (2) compressed. Thus full movement of the rack can be controlled by the governor while the engine runs will adequate oil pressure.

As oil pressure falls below 8 psi (0,56 kg/cm2), the force of spring (2) moves piston (3) to contact the shutoff lever (5) and moves the rack to shutoff position.

Any oil exhausted through passages (4) in piston (3) drains oil from the governor cover through tube (6) to the crankcase.

The use of a water temperature valve (7) connected with the oil supply tube will simulate oil pressure failure, thus affecting shut down of the engine.

1. Control lever. 2. Spring. 3. Piston. 4. Oil passage. 5. Shutoff lever. 6. Tube. 7. Water temperature shutoff valve.

Gas Shutoff Valve
It is necessary to push the reset button to start the engine. When the engine is stopped, a solenoid on the gas valve is activated by the magnetic switch. The solenoid then closes the gas valve and connects the magneto to ground. The solid state ignition system requires a different gas line valve than the standard spark gap magneto system.


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