Post on 17-Dec-2015
Control Valve Performance
Does the Valve Move?Is the assembly capable of small control steps
over the range of useHow Fast Does the Valve Move?
Does the valve get to setpoint quickly when changes are made
Does the valve overshoot?How Stable is the Valve at Steady State?
Negative gradientsCavitation
Process Benchmarking - Variability
80% of control loops demonstrate excessiveprocess variability
30% due to control valve performance
The undesirable behavior of
control valves in the biggest contributor to
poor loop performance
Source: Entech---Resultsfrom audits of over 5000loops in Pulp & Paper Mills
Loops The Reason
Source ofVariability
Pneumatic Actuators
70% of the marketGood reliable actuationLow stiffnessLimited forcesWill overshoot/huntAir supply needed
Pneumatic Actuators
Pneumatic Positioners Guarantee that the
valve does in fact move to the right position
Used for better accuracyDiagnostics
Most are related to air
Hydraulic actuator
Very StiffFastHigh forcesVery energy inefficientHazardous fluidsTend to leak
Environmental problem
Difficult to maintain
Electric Actuator
Typically intermittent motorsCycled on and off For modulation, 3600
‘start’/hour needed
Uses physical limit switches to indicate valve closure/position
Position sensor potentiometer
Electric Actuator
Rotary to linear conversionWorm GearsBall screwsAcme screws
Not robust for high duty cyclesGear or ballscrew wearMotor burn-out
What If…..?
Electric actuator designed for modulating control Unaffected by valve stiction Perfect tracking of closed-loop controller
demand No dead time, lag, or overshootNo duty cycle (100% continuous torque)Fast responseLong life No maintenance
Motion Control Industry
Very precise positioningRapid repetitive motion (high duty cycles)High speedsLarge range of forcesHigh RepeatabilityHigh EfficiencyLow Maintenance
Design Criteria
Robustness to shock High speed High positioning
accuracy High response High mechanical
stiffness Moderate cost
High efficiency Very small size Low maintenance Completely sealed Rotary and Linear
designs Position Feedback
capable
Industrial Grade Electric Valve Actuator
Rotary to Linear Converter
Ball Screw TechnologyShort service lifeLow shock resistanceNearly impossible to clean and regreaseRotational speeds limited to ~ 1,000 rpmNoisyTricky disassembly
Rotary to Linear Converter
Roller screw TechnologyUp to 15x the travel life of a
(equivalent size) ball screwHigh Shock ResistanceEasy disassembly Easy cleaning and re-greasingRotational speeds up to 6,000
rpmDesign can be invertedQuiet operation
Ball Screw
Roller Screw
Roller Screws have Roller Screws have 15 times more contact area15 times more contact area
Load Points ( )
in the same spacesame space
Why Longer Travel Life?
Adjacent balls within a ball screw have conflicting friction leading to heating and wear.
Ball Screw
Roller ScrewRoller screw rollers are separated by journals.
Why More Efficient?
Why Higher Rotation Speeds?
Roller Screws
Ball ScrewsSharp turns of ball returns cause vibration and noise.
There is no loading and unloading of balls and no sharp turns of ball return tubes. Therefore, planetary roller screws operate efficiently up to 6,000 rpm.
Servo Motor vs Induction Motor
Small size High output relative to size and weight
AC induction motor 7.6in Brushless servo motor 3.5in
Closed loop feedbackResolver, Encoder, Hall effect
High efficiency (90%)All Voltages
24VDC to 460VAC
Servo Motor vs Induction Motor
High torque to inertia ratios Rapid acceleration
Reserve power (2x over continuous)
Cool runningcurrent draw proportional to load
QuietVibration free
Rotary Servo Motors
Very high torque densityHigh side load bearing designPlanetary Gear Reduction
Single and Double Reduction4:1 to 100:1
Digital Controller
Closed loop control of motorDigital/Analog feedbackPosition ControlForce (current) controlDiagnostics
Applying Technology to a Valve
Built in digital feedback
High Stiffness
Built in positioner
100% Torque at all times
Custom Valve Seat
High Repeatability
Extreme Accuracy
Fast Response
Fast Stroke
Steam Turbine Application
Steam Turbine Retrofit
GE turbine steam controlDirect replacement of 10
inch diameter single acting, hydraulic cylinder
Elimination of mechanical governor operated pilot valve.
Servo actuator with a 10 inch stroke
Handwheel for manual operation
Turbine Fuel Valve Control Application
Steam Turbine Retrofit Nuclear Power Plant
Feedwater TurbineRack seating 6 valves1100 lbf peak3” cylinder with 6”
stroke85% efficientMuch Lower Routine
Maintenance Better performance
Pilot Valve Control Application
Steam Turbine RetrofitTurbine pilot valve
Linear Servo Actuator High static and dynamic
control accuracy Stiction and friction problems
eliminated Control valve's oscillation
was eliminated thereby extending steam distribution system's life, and reducing spare parts costs.
Gas Turbine Control
Inlet Guide Vanes Precise positioning and
feedbackAbility to fine tune injector
airflow to maintain CO and NOx emissions.
Bleed ValveVariable air bleed valves
and inlet bleed heat valves
Fuel Metering ValveBall valves
Cooling Water
Centrifugal Pipe Casting Molten iron is poured into a
water-cooled rotating pipe mold
Cooling water is precisely controlled by linear actuators on globe valves
Speed of response was critical
Aluminum Plate
Production of Aluminum for the aircraft and space markets
Application: Quenching of aluminum plates
Flow control of water, 35 to 85 psi, 280 to 875 gpm.
21 Ball Rotary Control Valves21 Servo electric actuatorsOriginal actuators had problems
with deadband and hunting-seeking behavior
Damper Applications
Low-NOx (nitrous oxide) burners need accurate air flow
Windbox Dampers44 electric linear servo actuators
4 or 8 ‘corners’ retrofittedReplaced failing electric ballscrew
actuators