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stroke in proportion to control pressure. Full stroke is achieved at 19 bar.
By mounting an electrically modulated pressure control valve on the hydraulic stroker
to establish the control pressure, pump stroke is controlled by an electrical signal. At
150 to 200 mA electrical signal, the pump commences to stroke, and at approximately
390 mA, the pump will be at full stroke.
An override pressure compensator or a torque limiter control is mounted on the
on-stroke side of the control piston from the servo, hydraulic or electric stroker. The
port which connects to cylinder in the at-rest position is connected to servo, allowing
normal stroker control. When system pressure or torque exceed the override setting,
system pressure is supplied to the smaller diameter control cylinder to override the
command and reduce stroke to the compensator or torque limiter.
INTRODUCTION
ELECTRIC STROKER
PRESSURE COMPENSATOR
AND TORQUE LIMITER
OVERRIDE
5
TROUBLESHOOTING CHART
Effect of Trouble
Possible Cause
Fault Which Needs Remedy
Compensator, Compensator Override
Low system pressure
Compensator malfunction
Dirt in spool orifice
Damaged cone or seat
Broken differential spring
Improperly adjusted differential spring
Failure to compensate
Differential adjustment
Differential set too high
Sluggish response
Differential adjustment
Differential set too low
Wide pressure fluctuations (hunting)
Excessive line capacitance
Install check valve near pump outlet
Load Sensing Control
Low system pressure
See above
Failure to compensate
See above
Sluggish response
Differential adjustment
Differential set too high
Modulating valve
Air in load sensing line
Wide pressure fluctuations (hunting)
Excessive line capacitance
Install check valve near pump outlet
Modulating valve
Air in load sensing line
Excessive pressure drop across
Differential adjustment
Differential set too high
control valve
Poor control of flow
Differential adjustment
Differential set too low
Torque Limiter, Torque Limiter Override
Torque setting erratic
Torque limiter cap malfunction
Sticking pin
Torque incorrect at high flows
Incorrect torque setting
Outer adjustment screw
Torque incorrect at low flows
Incorrect torque setting
Inner adjustment screw
Too much torque variation
Wrong torque limiter for range
Replace inner/outer springs with
correct springs
Low system pressure
Compensator malfunction
Dirt in spool orifice
Damaged cone or seat
Broken differential spring
Improperly adjusted differential spring
Failure to compensate
Differential adjustment
Differential set too high
Sluggish response
Differential adjustment
Differential set too low
Wide pressure fluctuations (hunting)
Excessive line capacitance
Install check valve near pump outlet
Rotary Servo
Failure to stroke
Differential adjustment
Differential set too low
Goes to full
Differential adjustment
Differential set too high
Sluggish response
Low servo pressure
Check servo pressure
Strokes in steps
Servo cap malfunction
Sticking pin
Wear on linkages or input cam surface
Hydraulic Stroker
Failure to stroke
Differential adjustment
Differential set too low
Goes to full
Differential adjustment
Differential set too high
Strokes in steps
Servo cap malfunction
Wear on linkages, Sticking stroker piston
Electric Stroker
Failure to stroke
Differential adjustment
Differential set too low
Goes to full
Differential adjustment
Differential set too high
Excessive hysteresis
Electric proportional valve
Change dither on electrical signal
No response
Electric proportional valve
Faulty wiring, Filter screen plugged
Strokes in steps
Servo cap malfunction
Wear on linkages
Sticking stroker piston
Instability
Air in control
Bleed air from control
Check for air in servo supply
General
Cannot achieve full volume
Maximum volume stop
Back out max. volume stop
Cannot achieve zero volume
Minimum volume stop
Back out min. volume stop
Noise
Air in system
Aerated reservoir
Leaky inlet line
Trapped air in system
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