Governors for Marine Diesel Engines-maintenance and troubleshooting

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In this post, we will discuss the best Operations and Maintenance of Governors for Marine Diesel Engines. This post will be useful for Practicing Marine Engineers and Marine Engineering students.

Diesel Engine Governor-Control System-Governor Basics

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Governor is the most important device in an engine that controls the speed automatically in the defined limits. Governor performs this function in the following two steps.

1. Measurement of speed
2. Fuel supply control to the machine.

Governors are used in a Diesel Engine

To keeps the engine running at a steady speed with the control of fuel supply irrespective of load.

Governor located in an Engine above the flywheel near the engine starting control panel.

1. Hydraulic type
2. Mechanical type
3. Inertia type
4. Electronic type

Type of Governor used on ships.

1. Governor used for the Auxiliary Engine(generator) is a droop speed governor with over speed trip.
2. On Main Engine it is a constant speed Governor with over speed trip function. The importance of over-speed trip fitted in the main engine is for the following important factors.
3. A sudden increase in speed and sudden change of load. This type of condition might arrive due to a loss of propeller in the rough sea.
4. Over speed, a trip is provided to safeguard against the damage of parts.
5. Over speed, the trip is attached to the camshaft through gear arrangements.
6. Over speed, the trip device cuts off the supply in the event of speed rising above 10 to 15% above the rated speed.
7. Manually reset is required before the re-start of the engine.

The hydraulic governor is used for the following purpose.

• Sensitivity
• Isochronous.
• Have the more high power to operate the fuel control mechanism.

Erratic increase or decrease of speed due to over control of fuel supply is known as hunting. Hunting is caused due to the unavoidable time lag between the governor movement and response of the engine.

• It is % of the difference between the no-load speed and full load speed.
• Rapid swing is resulted due to small droop.
• A slower response is resulted due to the large droop setting.
• Isochronous Governor is a constant speed governor.
• Isochronous Governor has the ability to maintain the speed with zero hunting.
• The Governor which has proportional and reset is known as Isochronous Governor.

1. Increasing the engine speed by speed adjuster at no-load condition
2. Over speed, the mechanism should shut off the fuel supply at 115% of normal speed.

Important reasons for using the Speed Droop Governor in generator Engine

2.To function in harmony with AVR of Alternator

1. Speed is controlled within prescribed limits by the governor.
2. Rise of speed more than 15 % of the rated speed in the event of an accidental change in load from full load to no load.
3. Parts may damage in the event of sudden over-speed due to the time delay action of Governor Control.
4. For the above reasons the Over speed trip is provided.

Operation of Isochronous Governor

1. Isochronous Governor maintains the constant speed without hunting.
2. Isochronous Governor has the temporary speed droop.

Sensitivity of a governor

Is the ability of a governor to control the speed in narrow limits?

Types of Maintenance carried out on Board a Ship

1. Periodically check of Oil
2. Change of Governor oil
3. Greasing of linkages and joints

Governor function in details (Governors for Marine Diesel Engines)

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If a diesel engine is to be operated within a specific speed range and under varying loads, a mechanical device must control the amount of fuel injected. This device is called the governor.

The speed of a diesel engine depends on two factors. (Governors for Marine Diesel Engines)

1. The amount of fuel injected into the cylinders
2. Load under which the Engine works.

Let us consider the Engine is running at a certain speed. The Engine slows down upon the increase in load. If, on the other hand, the load should decrease with no change in the amount of fuel injected, the Engine speeds up. By regulating the amount of fuel injected, it may keep the engine speed within a specific range. To do this, various types of governors have been developed. The operating principle of most governors is centrifugal force. Centrifugal force is the tendency of an object when traveling a circular path to move away from its rotation axis. These rotating weights are affected by this force as the speed is increased. Weights are pushed from their axis by the more vital centrifugal forces. Speed of rotation is proportional to the distance from the axis.

Over-speed governor is one type of governor. The speed governor prevents Engines from speeding or racing. The basis of the over-speed governor is a pair of flyweights mounted on the driveshaft. The outward motion of the flyweights is transmitted to a collar. Which slides on the shaft? The movement of this collar actuates a linkage to the fuel pump controls. A spring presses upward against the collar. As the Engine operates at average speed, the flyweights tend to move outward. Spring retards the movement. But should the engine speed increase to a point where the safe speed limit is exceeded, the flyweights’ centrifugal force becomes excellent enough to depress the spring. This decreases the Engine speed by reducing the amount of fuel injected. The diesel engine is prevented from over speeding by over speed governor.

One design of over speed governor called the over speed trip Is sometimes used to stop the Engine completely when a safe speed is exceeded. This type of over-speed trip has only one flyweight also working on the principle of centrifugal force. While the Engine operates at a safe speed, the rotating flyweight is held close to the driveshaft by a spring. Flyweights trip a latch by moving outward during the over speeding of the Engine. This causes the Engine to stop shutting off the fuel supply to the injection valves.

Consider repeating the action in steps. The flyweight is held to the drive shaft by a spring. When the Engine speeds centrifugal force overcomes the resistance of this spring, and the flyweight moves away from the shaft. In this position, the rotating flyweight trips the latch, which releases the spring-loaded plunger. The plunger pushes against the fuel cut-out lever, which in turn moves the fuel pump control to the no injection position, and the engine stops.

Before the Engine can be started again, the latch and the fuel pump must be reset. This is done by this reset arm which is mounted on the reset lever shaft.

The fuel cut-out cam mounted on the Engine’s control shaft is used when stopping the engine by hand. Cam turns the cut-out lever and shuts off the fuel pumps when the Engine’s starting lever is moved to stop.

The regulating governor not only keeps the Engine from over speeding but maintains the engine speed at a fixed rate despite changes in load. In this governor, the flyweights are linked hydraulically to the fuel control assembly. A piston connected to the fuel system controls a housing spring is part of this assembly. The downward pressure of the spring is balanced by oil pressure on the lower side of the piston. The amount of oil in this space is regulated by a valve called the pilot valve controlled by the flyweights.

When the engine is running at a set speed the port to the power cylinder is covered by the pilot valve plunger. The plunger is held in this position by the flyweights. if the engine load decreases however the engine speeds up and the additional centrifugal force throws the flyweights outward raising the pilot valve plunger. Thus the pilot valve plunger uncovers the port and oil from the power cylinder flow to drain passage through the pilot valve cylinder. The power spring forces the piston down actuated the linkage to the fuel system controls and the supply of fuel to the engine cylinders is diminished. As the engine speed returns to the set rate the flyweights resume their original position and the pilot valve plunger again covers the port. The flyweights move inward if the load decreases. Inward movement of flyweights causes to lower the pilot valve plunger allowing the oil to flow from the pilot valve chamber to the power cylinder. This oil supplied by a pump is under a pressure sufficiently high to overcome the pressure of the power spring. The power piston increases the amount of fuel injected by its upward movement.. Once again as the speed returns to the set rate the flyweights resume their central position. The gear pump which supplies the high-pressure oil is driven from the governor driveshaft and takes suction from the governor oil sump. Return of excess oil to the sump is affected by the spring-loaded accumulator which maintains the stable head.

To increase the regulating governor’s sensitivity and to prevent overcorrection a compensating mechanism is used. The compensation mechanism enables the pilot valve port to keep open for a suitable period for the engine speed to return back to pre-adjusted speed.

A compensating plunger on the power piston shaft moves in a cylinder that is also filled with oil. When the engine speed increases and the power piston moves downward the compensating plunger is also carried down drawing oil from a cylinder below the pilot valve bushing. This creates suction above the receiving compensating plunger which is part of the bushing. The bushing moves upward closing the port to the power piston. Hence the power piston in stop conditions to disable the overcorrection. As the flyweights and pilot valve returned to their central position Oil flowing through a needle valve allows the compensating spring to return the pilot valve bushing to its central position. Bushing and Plunger should come down at a similar speed for closing the port. Therefore adjust the needle valve to ensure the pass of oil at a suitable rate for the particular engine.

The actuating compensating plunger moves upward with the power piston during the reduction of speed below its nominal set range. This increases the oil pressure above the receiving compensating plunger. The compensating plunger travels down along with the pilot valve bushing.

As before the port leading to the power, the cylinder is closed. the excess oil in the compensating system now drains out through the needle valve as the spring returns the bushing to its central position. By changing the tension of the speed adjusting spring the speed of the engine is set.

Oil allowed to leak past the various plungers for lubrication purposes is drained into the governor oil sump .these are the basic elements of this type of regulating governor In actual operation.

We shall review the functioning of the governor and maintain the engine speed under the sudden increase of load. A drop in engine speed takes place and the pilot valve plunger is lowered by the inward movement of flyweights.

Oil from the gear pump and the accumulator forces the power piston upward increasing the amount of fuel injected into the engine cylinders. in the meantime, the pilot valve bushing has moved downward closing the port in the pilot valve. As the engine speed returns to normal the flyweights and the pilot valve plunger and bushing returned to their central position .now if the load suddenly decreases and the engine starts to race the flyweights move outward lifting the pilot valve plunger.

The decreasing of injected fuel amount is affected by the movement of the power piston due to the oil drain from the power cylinder. In the meantime, the pilot valve bushing has moved upward closing the port in the pilot valve. Flyweights, plunger, and bushing resume their original position upon the normalization of engine speed. Always keep the governor clean and keep it free from dirty lubricating oil. Flush it out every two weeks with clean fuel oil. Flush it out every six months with carbon tetrachloride. Refill it with lubricating oil of the viscosity specified by the operator’s manual. Be sure that the oil is always at the proper level keeping it above five-eighths of an inch in the gauge glass never. Never tamper with the governor unless you are positive that there is some trouble with it and even then all repairs should be made only by experienced personal.

Famous brands of Governors

Woodward

hydraulic-mechanical governors provide reliable and precise control of engine speed and output in virtually every type of engine application. Woodward governors are used in power generation, marine, pump, compression, and vehicle applications. Available in work output ratings from 10.8 in-lbs up to 500 ft-lbs.

Regulateour Europa

is the world-class governor for the control and monitoring solutions. These Governors are used for Mechanical and electronics Governors and control systems for marine, traction, industrial and offshore applications.

Frequently Asked Questions

What is Governor?

Governor is the most important device in an engine that controls the speed automatically in the defined limits

What is the Hunting of Governor?

Erratic increase or decrease of speed due to over control of fuel supply is known as hunting. Hunting is caused due to the unavoidable time lag between the governor movement and response of the engine

What is Governor Droop?

It is % of the difference between the no-load speed and full load speed

What is Isochronous Governor?

Isochronous Governor is a constant speed governor

Conclusion

I hope that the post Learn the best Operations and Maintenance of Governors for Marine Diesel Engines has been useful for the reader. I welcome the comments for the improvement of the post

Originally published at https://www.marinediesel.co.in on April 11, 2021.