MOV/Gearbox Overtorque Protection

Presented By: Denise Lane Mech. Engineer

Agua Fria Generating Station

(Ex: Limitorque Actuators)Power Generation

Best Practice’s Meeting

October 31, 2007

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-000Integral 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?

Protection Collar – Calculations Needed

• Formula Derivation – (4) Steps– Parker/Winsmith Gear Speed Reducers

• Limitorque SMB-00 Actuator Supplier

– Pinnacle Actuation• MOV/Gearbox Safety Training

– SRP Engineering

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Protection Collar – Calculations Needed

Step 1. Actuator Input ParametersMaximum Actuator Torque Input 156 ft*lbsMinimum Actuator Angular Speed Input 12 rpm for 0.7 hp Motors

17 rpm for 1 hp MotorsNote: 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 NeededStep 2. Operating Output

Max. Steam Pressure to Overcome in Fully Open Line 445 psigFlexible Wedge Diam. 6 in Flexible Wedge Seating Area 29 in. 2̂Stem Diam. 1.50 inStem Loading Area 1.77 in. 2̂Seating Force 3,838 lbs.Stem Load 786 lbs.Stem Packing Friction 3,000 lbs.Max. Seating & Unseating Thrust 7,624 lbs.Max. Gear Torque Output Required 88 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 NeededStep 3. System Supply Adjustments

Max. Horsepower 0.7 hpWorm Gear Input RPM - All Motors 1,700 rpmMotor Torque Input 2.2 ft.*lbs.Max. Speed Reducing Gear Ratio Supplied 80Constant Valve Stem Speed 21.25 rpmMotor Efficiency 0.61Max. Output hp 0.427 hpMax. 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 NeededStep 4. Torque Overload Protection Required 95 ft.*lbs.

Handwheel Shaft Length & Wheel Radius Vector 0.96 ft.Rim Pull Force Needed 98 lbs.Available UnLevered Torque per AS2638 56 ft.*lbs.Max. Extension Lever Required 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?