Transcript Slide 1
MOV/Gearbox Overtorque Protection
(Ex: Limitorque Actuators) Power Generation Best Practice’s Meeting October 31, 2007 Presented By: Denise Lane Mech. Engineer Agua Fria Generating Station
Presentation Elements • MOV/Gearbox Safety Concern Refresher – Crystal River – Common Causes of Failure – Valve Wrench/Cheater Bar Usage • Mechanical Overload Protection Device – Operating Principle – Information & Calculations – Installation & Cost
MOV/Gearbox Safety Concerns •Crystal River - 01/2004 – BFP Iso Valve •Killed 20 Yr. Employee •Valve Wrench To Close •Gears Cranking to Open •Cracked Actuator Housing
MOV/Gearbox Safety Concerns • Valve Failure Root Causes – Using a Valve Wrench/Cheater Bar on the
Handwheel
– Holding In the Motor Control Contactor – Setting the Torque Switch Too High – Beating on Valve Body to Unseat Valve – Removing Stem Locknut Under Pressure – Electrical Shock
Safety – Handwheels & Valve Wrenches • Handwheel Torque > Motor Torque • Wheel Radius & Max. Hand Forces Limit Torque −Designed for Max. Allowable Actuator Rating
Safety – Handwheels & Valve Wrenches • Valve Wrenches/Cheater Bars −Benefit - Decreases Hand Force Needed to Seat or Unseat Valves −Drawback - Uncontrolled Length
Increases Induced Weak Link Stress
−Drawback – “Slipping” Safety Concern
Safety Concerns • Weak Links Can Stretch & Separate – Yoke & Actuator Housing Cover Bolts – Causes Actuator &/or Valve Housing Ejection – “Missile” Safety Concern – Not Just Limitorque – More Often Now
Overtorque Protection Collar – How It Works
Protection Collar – Other Styles
Top Mounted D82 Model D82TM-INT SMB-000 Integral part of Limitorque actuator
Protection Collar – Information Needed
• Valves – Make & Model/Style – Stem Diameter & Threads/Inch • Actuators – Make & Model/Style – Shaft Diameter – Keyways • Width x Length x Depth • Length Extended Through Handwheel Collar?
• Extruded or Inlaid?
• Formula Derivation – (4) Steps – Parker/Winsmith Gear Speed Reducers • Limitorque SMB-00 Actuator Supplier – Pinnacle Actuation • MOV/Gearbox Safety Training – SRP Engineering
Protection Collar – Calculations Needed
Step 1.
Actuator Input Parameters
Maximum Actuator Torque Input Minimum Actuator Angular Speed Input 156 12 17 ft*lbs rpm rpm for 0.7 hp Motors for 1 hp Motors
Note: NO Actuator Torque shall Exceed 260 ft*lbs for SMB-00 In Addition, the Motor Supplier Limits Motor Parameters Further to 60% of this Value = 156 ft*lbs
•Determine Actuator Parameters •Limitorque SMB-00 = 260 ft*lbs Max. Input •Aura Motor = 260 x 0.6 = 156 ft*lbs Max. •rpm = hp x 5252/Torque −Min. Angular Speed < Step 3 Ensures Max. Torque Not Exceeded
Protection Collar – Step 1 Information •Actuator Nameplate Service Factor •Maximum Allowable Torque Input •Motor Manufacturer Safety Factor
Protection Collar – Calculations Needed
Step 2.
Operating Output
Max. Steam Pressure to Overcome in Fully Open Line Flexible Wedge Diam.
Flexible Wedge Seating Area Stem Diam.
Stem Loading Area Seating Force Stem Load Stem Packing Friction Max. Seating & Unseating Thrust
Max. Gear Torque Output Required
445 6 29 1.50
1.77
3,838 786 3,000 7,624
88
psig in in.^2 in in.^2 lbs.
lbs.
lbs.
lbs.
ft.*lbs.
•Gear Output = Min. Torque to Open/Close Valve •Wedge Diameter = Valve Diameter •Seating Force = Line Pressure x Seating Area x
Valve Turning Hardness Factor
•Required Output = Total Thrust x Stem Radius
Protection Collar – Step 2 Information •System Line Pressure •Valve Internal Diameter •Valve Stem Diameter •Valve Friction Coefficient: −Gate = 0.3 •Packing Friction Coefficient −Graphite = 3,000 psig incl. S.F.
Protection Collar – Calculations Needed
Step 3.
System Supply Adjustments
Max. Horsepower Worm Gear Input RPM - All Motors
Motor Torque Input Max. Speed Reducing Gear Ratio Supplied
Constant Valve Stem Speed
Motor Efficiency
Max. Output hp 0.7
1,700
2.2
80
21.25
0.61
0.427
hp rpm
ft.*lbs.
rpm hp Max. Gear Torque Output 106 ft.*lbs.
•Supplied Gear Output = Max. Actuator Torque •Input = hp x 5252/rpm •Stem Speed = rpm/Drive Sleeve Bevel Gear Ratio −Must be > Step 1 Min. Calculated Speed Input •Gear Torque = Output hp x 5252/Stem Speed
Protection Collar – Step 3 Information •Motor hp •Motor rpm •Motor Efficiency •Drive Sleeve Bevel Gear Ratio
Protection Collar – Calculations Needed
Step 4.
Torque Overload Protection Required Handwheel Shaft Length & Wheel Radius Vector Rim Pull Force Needed
Available UnLevered Torque per AS2638
Max. Extension Lever Required 95 ft.*lbs.
0.96
98 ft.
lbs.
56 ft.*lbs.
11.96
in.
•Required Torque < Overload Protection Cutoff
< Max. Actuator Torque
•Vector = Moment Arm Length About System C.G. •Hand Force = Cutoff Torque x Vector •Max. Bar Length Allowed = Cutoff Torque - Avail. Hand Torque_____
Hand Force Needed – Avail. Hand Torque
Protection Collar – Ease of Installation/Pricing •$1,000-$1,500 Ea.
Dependent on Qty. & Style
•Greg Bennett –
“Relatively Easy”
•Kirk Mason –
“Very Easy” “Piece of Cake”
•Successfully Tested
Collar Installed on FWH Extraction Valves No Collars Collars
Questions?