Compensation System
If the pilot valve plunger is lowered, pressure oil flows to the bottom of the power
piston pushing it up, lifting the terminal lever, which in turn rotates the output
shaft.
As the power piston moves up, the oil on top of the power piston is forced out
into the passage leading to the upper side of the buffer piston, and to the lower
side of the compensation land on the pilot valve. The buffer piston moves down,
partially relieving the compression of the upper buffer spring and increasing the
compression of the lower buffer spring. The force change of the buffer springs
tends to resist this movement, resulting in a slightly higher oil pressure on the
upper side of the buffer piston. This higher pressure is transmitted to the
underside of the compensation land of the pilot valve plunger. The pressure on
the lower side of the compensation land produces a force which acts to push the
pilot valve plunger back to its centered position.
The force of the pressure differential on the compensation land moves the pilot
valve towards its centered position. Due to the compensation forces, the pilot
valve re-centers, although the engine speed is not back to normal. Leakage of oil
through the needle valve orifice equalizes the pressures above and below the
compensation land, and allows the engine speed to return to normal. As the
pressures above and below the compensation land become equal, the buffer
springs return the buffer piston to the centered position.
Speed Droop
The 3161 governor is an isochronous governor with the ability to operate in the
droop mode by the adjustment of the internal droop pivot pin. The governor may
be used in the droop mode to allow for load division between two or more prime
movers connected to a single shaft or for operating in parallel.
The droop pivot pin is attached to the terminal lever located inside the governor.
if droop has been set, the following occurs: As the output shaft of the governor
rotates in the increase direction, the compression of the speeder spring is
reduced, which in turn reduces the governor speed setting. The speed of the
prime mover is reduced as load is applied. As the output shaft of the governor
rotates in the decrease direction, the compression of the speeder spring is
increased, which raises the speed setting of the governor as load is decreased.
Limit/Shutdown Pilot Valve
Shutdown of the prime mover is accomplished with the limit/shutdown pilot valve.
With the prime mover running on speed, the ballhead pilot valve is in the
centered position. When the limit/shutdown pilot valve is lowered, pressure oil
above the control land of the ballhead pilot valve is drained back to the sump
area. As prime mover speed begins to slow, ballhead flyweights move in,
lowering the ballhead pilot valve plunger. Oil under the power piston is then
drained to the sump area. As the power piston moves down, the output shaft is
rotated in the decrease direction, and the prime mover is shut down.
