Manual 89015
Hydraulic Amplifier (Electrical Input)
Woodward
1
Chapter 1.
General Information
Description
The electrically controlled hydraulic amplifier is a linear, pilot-valve-operated
servo actuator. It is used when a large force is needed to operate power control
mechanisms such as turbine steam valves and fuel control linkages of large
engines. An EG-3P proportional actuator is used to electrically control the
hydraulic amplifier.
The EG-3P proportional actuator is installed under the cover of the hydraulic
amplifier. The EG-3P actuator changes a low-level electrical input signal to a
rotary mechanical output. This output, through mechanical linkage, controls the
movement of the amplifier pilot valve plunger. The amplifier pilot valve sends
high-pressure control oil from the prime mover lubricating system or an external
pump to the increase side of a differential servo cylinder. Some amplifiers have a
single-acting servo cylinder with a spring return. The servo piston is moved in the
decrease direction by oil at supply pressure and the return spring pushing on the
bottom side of the servo piston. The piston is connected to the power control
mechanism of the prime mover.
Pressure oil against the top side of the piston opens the fuel or steam control
valve. A return spring applies pressure on the bottom side of the piston to
balance the force of pressure oil. This gives a balanced system with a linear
response through the full stroke of the amplifier.
The return spring returns the servo piston to the closed position on loss of oil
pressure. It also keeps the control valve in the closed position when the amplifier
is not in use. In other applications, the return spring gives only a low force biasing
load. Return springs for the 7-
1/4” (184 mm) amplifier are available from 50 to
2000 lbs (222 to 8896 N) compression. Return springs for the 5-
1/4” (133 mm)
amplifier are available from 50 to 400 lbs (222 to 1779 N) compression.
Two models of electrically controlled hydraulic amplifiers are described in this
manual. The work output of either model is proportional to the oil pressure and
length of the output stroke used. The basic difference in the two models is the
diameter of the servo cylinder. The work output of the 7-
1/4” (184 mm) diameter
servo cylinder (large model) can be up to 3000 ft-lb (4068 J) at the maximum
stroke of 3” (76 mm) at 500 psi (3448 kPa) oil pressure (maximum). It develops a
stalled force of approximately 12 000 pounds. The work output of the 5-
1/4” (133
mm) diameter servo cylinder (small model) can be up to 1000 ft-lb (1356 J) at the
maximum stroke of 2-
1/2” (64 mm) at 500 psi (3448 kPa) oil pressure
(maximum). It develops a stalled force of approximately 4700 pounds.
Extend to Increase Models
Extend-to-increase models are available. These units reverse the wiring on the
EG-3 actuator (
– to A and + to B). If a return spring is used, the actuator will
cause the valve to open on loss of oil pressure. In most instances, the return
spring is left out of the amplifier and an external return spring is provided by the
user.
Start oil cannot be used in the extend-to-increase models.