Centrifugal Pump

The basic centrifugal pump has only one moving part: a wheel or impeller that is connected to the drive shaft of a prime mover and that rotates within the pump casing. The impeller is designed to impart a whirling or revolving motion to the liquid in the pump. When the impeller rotates at relatively high speeds, sufficient centrifugal force is developed to throw the liquid outward and away from the center of rotation. Thus the liquid is sucked in at the center, or eye, of the impeller (center of rotation) and discharged at the outer rim of the impeller.

The centrifugal pump, like the diaphragm pump, is driven by a single-cylinder, four-cycle, air-cooled _{gasoline engine.} To operate the engine properly, you should be familiar with its controls.

NOTE: Refer to the operator's manual for specific instructions for the type of pump you are operating.

OPERATION.- The operation of centrifugal pumps is generally similar to the operation of diaphragm pumps. Centrifugal pumps (fig. 14-34) are also fitted with stuffing boxes and various types of bearings that require periodic operator's maintenance and inspection.

Figure 14-34.-Centrifugal pump.

NOTE: Unlike positive displacement pumps, the discharge stop valve on centrifugal pumps must be closed before starting the pump.

The reason for closing the stop valve is to allow the pump to work against the sealed discharge and buildup an effective pressure head before attempting to move and distribute the liquid downstream. After the pump is up to speed and the discharge valve is opened, it will continue to maintain that pressure head unless the operating conditions change.

There is no danger of building excessive pressure while the pump is running with the discharge closed. If the centrifugal pump were permitted to continue operation with the discharge sealed, it would simply build up toward its maximum discharge pressure and then begin to churn the liquid; that is, the discharge pressure would overcome the suction pressure and the liquid would continually slip back to the suction side of the pump. Nothing more would happen, except that the pump would build up heat since the liquid would not be able to carry away heat generated by the moving parts.

INSPECTION.- There is little for you to inspect other than routine operator's maintenance. If you follow all of the operator's manual instruction and the pump does not function properly, call for a field mechanic or turn it in to the dispatcher with a hard card for repair.

SWEEPERS

Many different types of sweepers are used in the Navy. Some of the most common are the towed sweeper, the street sweeper, and the magnetic sweeper.

Figure 14-35.-Towed sweeper.

Towed Sweeper

The NCF primarily uses the towed sweeper (fig. 14-35). Its size and easy maintenance give it an advantage over the street sweeper. Its disadvantage is that it requires a prime mover and windrows the debris to one side or the other only and does not pick it up.

Street Sweeper

The Navy also uses different types and makes of _{street sweepers,} the most common being the self-propelled type. The self-propelled street sweeper (fig. 14-36) is used mainly to remove loose debris from the surface of streets, roads, parking areas, taxiways, and airport runways.

Operational procedures to adhere to when operating a street sweeper are as follows:

. During sweeper operations, you should plan ahead and select routes where water is available to refill the water tank of the sweeper. This effort saves time and the expense of having to travel long distances to refill.

. The sweeper is equipped with a prime mover, controls, and devices for controlling movement of the basic machine for steering, sweeping, and water spraying, as well as for picking up, containing, and disposing of debris.

l When refueling a street sweeper, make sure the engine is turned off and see that metal-to-metal contact is maintained with the fuel tank and fuel nozzle.

l Keep personnel away from the brushes and scrubbers of the sweeper during operation

. Always stop operations when adjusting, cleaning, and lubricating the equipment.

. Keep hands clear of drive chains.

. Park the sweeper on level ground with the hand brake applied.

. Except in emergencies, do not turn the steering wheel sharply when the machine is in motion. The sweeper is highly responsive to small movements of the steering wheel.