Many marine engine installation practices apply equally to dredges.
When this is the case, the reader will be referred to the appropriate marine engine section. Only those practices and recommendations that are unique to the dredge application will be discussed in this section.
Mounting and Alignment Mounting Rails
All large bore Vee-type engines should be mounted with angle section, ledge-type marine mounting rails. Engines can be successfully installed using industrial channel section mounting rails, but mounting flexibility is sacrificed. See Marine Mounting Recommendations section for fur-ther details on shimming and bolt fit.
Tandem Engine Thermal Growth Considerations
The thermal expansion of engines must not be restrained. The flywheel end of the engine mounting rails should be fixed by a ground body, fit-ted bolt on either or both sides of the engine. The diameter of the mount-ing bolts – fixmount-ing the engine’s rails to the dredge structure – forward of the flywheel must be 0.06 in. (1.6 mm) less than the diameter of the holes in the mounting rails. This clearance will allow the engine and mounting rails to grow without confinement.
When installed properly, there is sufficient axial clearance within the Caterpillar viscous damped engine-to-engine coupling to allow the engine nearest the load to grow without restraint. The axial clearance dimension can be checked on a new installation by measuring from the outer face of the grease retaining plate (of the Caterpillar viscous damped coupling) to the nearest surface of the coupling inner mem-ber. This dimension should be 0.34 ± 0.03 in. (8.6 ± 0.76 mm).
Tandem Engine Timing Considerations
Timing Recommendations are contained on Tandem Engine Coupling Arrangement drawings. These directions must be followed to avoid possible torsional vibration problems.
FIGURE 1.20
Tandem Engine Governor Settings (Low Idle rpm)
Some dredge pump drive applications require a special engine low idle setting to avoid torsional resonance. Many Caterpillar engines used in tandem service must have a low idle setting of not less than 600-650 rpm. Always check the engine data plate to determine proper gov-ernor settings. Many dredge engine settings are special and not listed
AXIAL CLEARANCE DIMENSION
DRIVEN EQUIPMENT SHAFT OR HUB
COUPLING INNER MEMBER
GREASE RETAINING PLATE RUBBER ELEMENT CATERPILLAR VISCOUS DAMPED COUPLING
ENGINE FLYWHEEL
be troublesome. Fuel system maintenance is especially important in dredge applications.
The lowest point within the dredge’s fuel tanks should be drained or pumped daily to eliminate condensed moisture and sediment.
Water and sediment traps should be used in fuel supply lines.
Terminate engine fuel supply plumbing at least 12 in. (300 mm) above the lowest point in fuel tanks.
See fuel section for information on detection and prevention of fun-gus/bacteria growth in fuel tanks.
Exhaust, Ventilation, and Crankcase Vent Systems
All diesel engines require large quantities of clean, cool air for long trouble free life.
Combustion Air
Equip dredge engines with combustion air inlet ducts, located and routed to prevent recirculation of exhaust gases and crankcase fumes.
Locate combustion air inlets so they do not ingest heated engine room ventilation air rising through removable roof caps. Exhaust gases must be discharged to atmosphere high enough above the combustion air inlet openings to prevent rebreathing of exhaust gases. Equip exhaust stacks with joints which allow addition of extra sections of exhaust pipe if exhaust recirculation proves to be a problem on operating location.
An unrestricted elbow-type exhaust discharge fitting is preferred over the counterbalanced flapper valve because there will be less chance for downward deflection of exhaust gases.
See Ventilation and Exhaust sections for flow, pressure, and tempera-ture information.
FIGURE 1.21
Ratings
Engines in dredge pump drive service should be applied at the con-tinuous ratings.
Engines driving electric or hydraulic cutterheads and/or winches may carry the intermittent or light duty commercial rating since neither cut-terheads nor winches are continuous loads.
Engines driving generators which supply lighting and service pumping power should be rated for prime power due to the continuous nature of lighting and pumping loads.
For additional explanation of Caterpillar engine rating philosophy, see Ratings section. As Far As Possible From Combustion Air
conditions require more than twice the surface area that would be required if the cooling surface had a five knot water velocity over the outside of the cooler. See Keel Cooler Area Requirement curves in the Marine Cooling System section for added information.
Heat Exchanger Cooling
Using inboard (shell and tube-type) heat exchangers may be trouble-some due to the highly abrasive particles suspended in the water com-mon to dredging operations. Cooling water suction line strainers are a necessity to minimize damage to pumps and heat exchangers tubes.
Use Caterpillar engine-mounted sea water pumps (particularly rubber impeller pumps) with the knowledge that their service life, when pump-ing water containpump-ing abrasive particles, will be significantly shortened.
Hydraulic Dredges will have, as one of their normal components, a
“service water” pump. This pump is usually designed for abrasive water service. The service water pump provides clean sea water, at higher pres-sure, for lubrication and flushing of the dredge pump and cutterhead lineshaft bearings. Use of excess flow from the service water pump is a superior alternative to Caterpillar engine mounted sea water pump.
Box Coolers
Box-type coolers offer many of the advantages of keel cooling and shell and tube coolers, particularly in dredging applications.
Aftercooler Cores
Although many dredges operate in freshwater ponds, lakes, and rivers, experience has proven that engine aftercooler cores suitable for sea or salt water are a necessity. The moisture-laden air surrounding any float-ing equipment will corrode the fins on the air side of nonmarine after-cooler cores severely limiting the heat transfer and possibly even restricting the combustion flow.
Controls
Single Engine Drive
Dredge engine controls are the same as conventional controls for engines in other pumping or electric power generation applications, with the exception of tandem or compound engines driving a single load.
Tandem/Compound Engine Drive
When multiple engines are tandemed (nose-to-nose configuration) or com-pounded side-by-side configuration with flywheel outputs (combined in gearing or with chains), the capability to share load equally at full load becomes important.
Load Share
Engines must share load equally so one engine, the one taking most of the load, will not wear out prematurely or fail. The precision of the
sharing of the load is only important at or near the engines full power capability (large fractions of the engine rating).
Hydra-Mechanical Governors
A way to ensure load share at full load is to adjust the air actuators on Caterpillar standard hydra-mechanical governors so both engines reach the same high idle speed (rpm) with the same air actuator pres-sure. The adjustment is normally done at the factory when pairs of engines are specified to be used in tandem or compound.
Isochronous Governors
Load sharing is more easily attained if governors capable of isochro-nous operation are avoided or adjusted to operate in a droop, or non-isochronous mode. Generally 5-10% droop is satisfactory.
Safety System Considerations on Tandem/Compound Engines Prelubrication System
Wire the oil pressure sensors included with prelubrication systems in series to prevent either tandem/compound engine’s cranking motor from engaging before both engines are prelubed.
Shut-down Devices
Sensors connected to automatic shut-down devices must be inter-connected on tandem/compound engines to insure both engines shut-down in the event of a malfunction in either engine.