To control an engine means to keep it run-ning at a desired speed, either in accordance with, or regardless of, the changes in the load carried by the engine. The degree of control required depends on two factors: The engines performance characteristics and the type of load which it drives. In diesel engines the speed and power output of the engine is determined by varying the amount of fuel that is injected into the cylinders to con-trol combustion. There are two principal types of governors: hydraulic and mechanical.

Hydraulic Governors

It is beyond the scope of this training manual to list all of the possible troubles which may be encountered with a hydraulic governor. This sec-tion deals only with the most common ones. Poor regulation of speed may be due to the faulty ad-justment of the governor or to faulty action of an engine, a generator, a synchronizing motor, a voltage regulator, or any piece of equipment which has a direct bearing on the operation of the engine.

Manufacturers state that 50% of all governor troubles are caused by dirty oil. For this reason,

Table 3-1.Troubleshooting Chart-Governor

every precaution should be taken to prevent the oil from becoming contaminated. Most hydraulic governors use the same type of oil that is used in the engine crankcase, provided it is absolutely clean and does not foam. You should change the oil in the governor at regular intervals, depending upon the type of operation, and at least every six months regardless of the operation. You must ensure that the containers used to fill the governors with oil are clean, and that only clean, new, or filtered oil is being used. You should also check the oil level frequently to ensure the proper level is maintained and that the oil does not foam. Foaming of the oil is usually an indication that water is present in the oil. Water in the oil will cause serious damage to the governor. After installing a new governor or one that has been overhauled, adjust the governor compensating needle valve even though it has previously been done at the factory or repair facility. This adjust-ment must be made with the governor installed and controlling an engine with a load. If this is not done, high overspeeds and low underspeeds after load changes will result and the return to normal speeds will be slowed. Maintenance and repair of each unit must be in accordance with the manufacturers maintenance manual and the PMS.

NOTE: When governor troubles are suspected, before performing any maintenance or adjustments, always disconnect the governor fuel rod end from the fuel control rack and ensure that there is no sticking or binding of the rack. This procedure is necessary to determine if the trou-ble is actually in the governor.

The chart in table 3-1 lists some of the probable causes of trouble which are common to most hydraulic governors. This chart should be used for training purposes only; it must NOT be used to troubleshoot a governor. Always use the applicable manufacturers instruction manual for troubleshooting. Following are the definitions of the terms used in the chart.

HUNT: A rhythmic variation of speed which can be eliminated by blocking the fuel linkage manually, but which will reappear when returned to governor control.

SURGE: A rhythmic variation of speed always of large magnitude which can be eliminated by blocking the fuel linkage and which will not reap-pear when returned to governor control unless the speed adjustment of the load changes.

JIGGLE: A high frequency vibration of the governor fuel rod end or engine linkage. Do not confuse jiggle with normal regulating action of the governor.