The schematic arrangement of the 3161 governor is shown in Figure 3-1, with
the governor pilot valve calling for increased fuel. The 3161 governor has a selfcontained oil supply (approximately 2.3 US qt/2.2 L). The oil passes from the
suction side to the pressure side of the gerotor pump as the drive shaft is rotated
by the prime mover. Pump pressure is regulated at approximately 100 psi (690
kPa) by the accumulator spring and piston. As the pressure increases, the
accumulator piston moves up in the cylinder until 100 psi (690 kPa) is obtained.
At this time, bleed ports in the piston are uncovered, and pump pressure is
regulated.
The pressure generated by the accumulator, determines the work capabilities of
the governor. Pump pressure is also used for the auxiliary devices installed on
the cover.
Increase in Speed Setting
Rotating the speed setting shaft clockwise (CW) increases the speed setting of
the governor. (The high speed stop screw limits the high speed setting of the
governor.) As the speed setting shaft rotates, the speed setting lever pushes
down on the floating lever which is attached to the speeder plug. The downward
pressure on the speeder plug compresses the speeder spring and overcomes
the centrifugal force of the ballhead flyweights to lower the ball-head pilot valve
plunger (pvp), increasing speed setting of the governor.
When the pvp is lowered, pressure oil moves under the power piston causing it to
move up, lifting the terminal lever and rotating the output shaft towards the
increase direction. Even before the prime mover has reached the new set speed,
the compensation system starts to re-center the pvp. As the power piston moves
up, the oil on top of the power piston is forced out to the buffer piston and to the
lower side of the compensation land on the pvp. The change in force on the two
buffer springs tends to resist the movement of the buffer piston, causing a slightly
higher oil pressure on the upper side of the buffer piston, with this pressure being
transmitted to the bottom side of the pvp compensation land. The difference in
pressures on the two sides of the compensation land produce a force which acts
to push the pvp back to its centered position.
Leakage, of oil through the needle valve orifice equalizes the pressures above
and below the compensation land, and allows the buffer piston to re-center
during speed changes. As the pressures above and below the compensation
land become equal, the buffer springs return the buffer piston to its centered
position.
Decrease in Speed Setting
Rotating the speed setting shaft counterclockwise (CCW) decreases the speed
setting of the governor (the low speed stop screw limits the low speed setting of
the governor). As the speed setting shaft rotates CCW, the force of the speed
setting lever on the floating lever is removed and the compression is reduced
from the speeder spring. Centrifugal force from the flyweights raises the ballhead
pilot valve plunger (pvp), uncovering the control port in the rotating bushing.
Control oil under the power piston now drains to sump, allowing the power piston
to move down. The output shaft rotates in the decrease direction, and the speed
(rpm) of the prime mover is decreased. The compensation system then brings
the governor under stable control.
