overspeed trip. Remember that all spring tension and
linkage adjustments to an overspeed are critical.
Instructions for these adjustments are found in the
manufacturers instruction manual. You MUST follow
Hydraulic overspeedtrips are extremely sensitive to
dirt. Dirt or lacquer like deposits may cause the trip to
bind internally. The speed-sensitive element and all
parts of the linkage and mechanisms incorporated with
the speed-sensitive element must be kept clean. When
painting around the engine, you must avoid allowing
paint to fall on joints, springs, pins, or other critical
points in the linkage.
The overspeed trip will not function properly if parts
arc bent, badly worn, improperly installed, or dirty, or if
their motion is restricted by some other part of the
engine. In some situations the driveshaft of the
overspeed trip may be broken; this would prevent
rotation of the flyweight and the overspeed trip.
Insufficient oil in the hydraulic trip may be another
source of trouble. You should maintain a proper oil level
as specified by the instruction manual.
The following are some general procedures you
should follow to keep the overspeed safety devices in
Keep the overspeed trip and its linkage clean.
- Remove the source of binding.
- Replace faulty parts.
Maintain a proper oil level in the hydraulic
Adjust the speed-sensitive element according to
the instruction manual.
- If the trip has been damaged, replace it with a
spare and completely rebuild or overhaul the damaged
one according to the instruction manual.
Test overspeed trips and governor mechanisms once
each quarter and after each major engine overhaul. To
verify if the safety device is in proper working order,
overspeed the engine. When you are making this test,
use a tachometer to check the speed at which the
overspeed mechanism will operate. These safety
devices should operate at the speed specified in the
engine instruction manual. If this information is not
available, the following values should be used for the
l For large, slow-speed engines, the value is 107
percent maximum-rated speed.
l For high-speed engines, the value is 110 percent
If there is any irregularity during testing, stop the
test and check the overspeed safety device and correct
the problem before continuing the test procedure.
This chapter has presented several common facts in
maintenance, repair, and overhaul of speed controlling
devices. Maintenance personnel must secure the
appropriate manufacturers instruction manual. No
repair, maintenance, or overhaul of these precision
pieces of equipment should be made until the
appropriate manual is obtained. You must read,
understand, and strictly follow the instructions from the
manufacturer. Be sure to pay particular attention to any
safety precautions given in these instructions.