01 General Control Valves Training.

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Control Valves types, control valves characterstics, affects on control valves due to various process fluctuations or cavitations or flashing and remidies.The model datasheets also included.

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01 General Control Valves Training.

  1. 1. Engineering Centre of Excellence ECoE - Doha, QatarInstrument training – 16th July 2011 General Control valves. Prepared by: Gavhane D.V.
  2. 2. General Control valves. BY:-DNYANESHWAR GAVHANEGeneral Control Valves. Prepared by: Gavhane D.V. 2
  3. 3. General Control valves. INTRODUCTION :- Control valves also called final control element are a most important element in the control system of a process plant. It is the last device in control loop. DEFINITION :- A control valve is a variable orifice used to regulate the flow of a process fluid in accordance with requirement of process. FUNCTION :- It absorbs the proper amount of pressure drop to maintain system balance under all operating conditions.General Control Valves. Prepared by: Gavhane D.V. 3
  4. 4. Features of Control valves. THERE ARE FOUR FEATURES OF CONTROL VALVES : Capacity Rangeability Characteristics Pressure drop CAPACITY : The capacity is normally measured as Cv (Flow Coefficient) which is defined as : “The number of US gallons per minute of water at 60oF that will flow through a valves with 1psi pressure drop . RANGEABILITY : Rangeability of a Control Valve is the ratio of the maximum to the minimum controllable flow.General Control Valves. Prepared by: Gavhane D.V. 4
  5. 5. Control valves and Flow Characteristics. The relationship between control valve capacity and valve stem travel is known as the Flow Characteristic of the control valve. The Curve shown are based on constant Pressure drop across the valve and called Inherent flow characteristics.General Control Valves. Prepared by: Gavhane D.V. 5
  6. 6. Linear Characteristics. Flow Capacity increases linearly with valve (stem) travel. In which the valve differential pressure drop is Constant over the travel range. Linear valve plug shall for liquid level control and control application requiring constant gain. LINEAR VALVE TRAVEL IS DIRECTLY PROPORTIONAL TO THE VALVE STROKE MORE THAN FOR SLOW 40% FLUID OF SYTEM TRANSFER PRESSURE PROCESS DROP ACROSS VALVEGeneral Control Valves. Prepared by: Gavhane D.V. 6
  7. 7. Equal Percentage Characteristics. Flow Capacity increases exponentially with valve trim travel .Equal increment of valve travel produce equal percentage change in existing Cv. Equal Percentage valve plug shall be used where only small percentage of system drop is available in Control valve. EQUAL INCREMENT OF VALVE TRAVEL PRODUCE AN EQUAL PERCENT FLOW CHANGE FOR FAST FLIUD HIGH TRANSFER RANGEABILITY PROCESSGeneral Control Valves. Prepared by: Gavhane D.V. 7
  8. 8. Quick Opening Characteristics. Provides large changes in flow for very small changes in lift or in which a maximum Cv is achieved with minimal closure member travel. It has too high valve gain. LARGE INCREASE IN FLOW WITH A SMALL CHANGE IN VALVE STROKE Quick opening valve are usually specified for “ON-OFF” Service such as sequential operation in either batch or semi continuous process and in self actuated control valve . When maximum valve capacity must be obtain quickly. Cage- A part of a valve that surrounds the closure member & can provide Quick opening flow characterization.General Control Valves. Prepared by: Gavhane D.V. 8
  9. 9. Cavitation.Cavitation is condition that occurs in liquid flow where the internalpressure of liquid at set point falls below vapour pressure and vapourbubbles form and at downstream rises above vapour pressure again.As this pressure recovers so that bubbles collapse and cavitation takeplace.It is possible to predict where cavitation will occur by looking pressurecondition and valve recovery factor.( sigma Method )Cavitation sounds like stone passing through the valve. PRESSURE PROFILE ACROSS P SINGLE SEATED CONTROL VALVE P Pv Bubble collapse Bubble form Vena ContractaGeneral Control Valves. Prepared by: Gavhane D.V. 9
  10. 10. Effect of Cavitation. Erosion in rotary plug valve body induced by cavitationGeneral Control Valves. Prepared by: Gavhane D.V. 10
  11. 11. Flashing.Flashing is condition that occurs with liquid flow where the Pressure failsbelow it . There are then two phases flowing ( i.e. Liquid and vapour )down stream.Several damage can occur inside a valve due to erosion caused by theimpact of liquid droplet traveling at high speed. P1 PRESSURE PROFILE ACROSS SINGLE SEATED CONTROL VALVE Pv Bubble form P2 Bubble continue down stream Vena ContractaGeneral Control Valves. Prepared by: Gavhane D.V. 11
  12. 12. Effect of Flashing. Typical trim erosion damage due to flashingGeneral Control Valves. Prepared by: Gavhane D.V. 12
  13. 13. Velocity Profile across Single seated Valve. P1 PRESSURE PROFILE ACROSS SINGLE SEATED CONTROL VALVE Pv P2 V2 V 1(Liquid) (Liquid)Pressure Recovery:- At vena contracta,the velocity is greatest & substantiallydecrease in pressure .Further down stream, as the fluid stream expands intoa large area, Velocity decreases and pressure increases. This phenomena iscalled Pressure recovery.As a general ,globe valves have Lower pressure recovery than Ball andButterfly Valves. General Control Valves. Prepared by: Gavhane D.V. 13
  14. 14. Piping Influence/Reynolds Number/Choked Flow.Piping Influenence:- Capacity reduction due to the presence of Reducer Up &Down stream of the valve. Correction factor will be available frommanufacturer .Reynolds Number :- For Reynolds number application such as viscous orsmall flow , the basic sizing equation can not be used withoutcorrection, since the equation is based on turbulence flow . Correction factorwill be available from manufacturer .(The ratio of dynamic forces to viscousforces)Usually the correction can be ignored when Reynolds number is greater than4000,the correction will be 10% or less .Choked Flow:- When the pressure at vena contracta drop below the vaporpressure of the liquids, bubbles will form in the stream .The formation ofbubbles causes a crowding condition at vena contracta which tends to restrictflow, and further increase in pressure drop will not produce increase in flow. In case of gas , choked flow means outlet velocity reaches sonic velocity.The limiting Pressure difference ΔPt is called Maximum allowable differentialpressure for sizing. General Control Valves. Prepared by: Gavhane D.V. 14
  15. 15. Contents of Control Valve:– Data Sheet PROJECT:- GPS DOC NO:- - SUB CONTRACTORCONTRACT NO:- DOC NO:- SHEET NO:- 1 OF 1 DOCUMENT SPECIFICATION AND DATASHEETS DATE:- CLIENT DOC NO:- NAME:- FOR CONTROL VALVES REV NO:- DATASHEET - CONTROL VALVES1 TAG GENERAL DATA2 SERVICE BLANKET FUEL GAS FROM OIL STORAGE TANK 0-T-36033 LINE NO. / PID NO. 0-14"-FG-43 0017-AA3-H(E) / S2-01-YS207019-PID-P-5004 Sht 1 of 24 FLUID TANK VENT/FUEL GAS CRITICAL PRESS. Pc5 UNIT MAX FLOW NORM FLOW MIN FLOW SHUT-OFF6 FLOW RATE m3/h 5166 1847 525.3 -7 INLET PRESSURE psi(g) 0.0568 0.093 0.0975 15 bar(g)8 OUTLET PRESSURE psi(g) 0.037 0.0087 0.00234 SERVICE CONDITION9 INLET TEMPERATURE Degree C 50 50 50 100(Note 1) - /kg/m3 /10 SPEC WT/DENSITY/ MOL WT /-/1.378/40.30 /-/1.378 /40.30 /-/ 1.381/40.30 - kg/kmole11 VISCOSITY /SPEC HEAT RATIO Cp / 0.00924/1.133 0.00924/1.133 0.00924/1.133 -12 VAPOR PRESSURE inH2O NA NA NA -13 REQUIRED CV -14 TRAVEL % 015 ALLOWABLE /PREDICTED SPL dBA < 85/ < 85/ < 85/ -16 SET POINT inH2O(g) 2.75 2.75 2.75General Control Valves. Prepared by: Gavhane D.V. 15
  16. 16. Contents of Control Valve:– Data Sheet. SINGLE-ACTING FAIL SAFE17 PIPE LINE SIZE & IN 14" & SCH20 56 TYPE SPRING RETURN –DIAPHRAGM TYPE LINE SCHEDULE18 OUT 14" & SCH20 57 MFR & MODEL VTS HEAT CONSERVATION19 PIPE LINE INSULATION 58 SIZE / EFF.AREA VTS (ELECTRICAL TRACING)20 VALVE SIZING ISA S75.01 59 ON/OFF MODULATING YES SPEC.& CODES ACTUATOR (PNEUMATIC) VALVE SEAT LEAKAGE21 IV AS PER FCI 70-2 60 SPRING ACTION ON FAIL CLOSE CLASS MAX ALLOWABLE22 61 VTS PRESS.23 62 MIN REQUIRED PRESS. VTS24 63 AVAILABLE AIR SUPPLY MIN NOR MAX DESIGN25 TYPE BUTTERFLY 64 PRESSURE kPag 400 850 900 100026 SIZE VTS 65 BENCH RANGE VTS ACTUATOR27 MAX PRESS./TEMP. VTS 66 VTS ORIENTATION28 BODY/BONNET MATERIAL A105 or A216 WCB 67 HANDWHEEL TYPE YES VTS AIR FAILURE LOCK29 LINER MATERIAL / ID 68 REQD. SET AT Note 5 RELAY30 69 AIR BOTTLE REQD. WITH ACCESSORIES VALVE BODY31 END CONNECTION IN/ OUT FLANGED 70 FIRE SAFE YES32 RATING & FLANGE FACE FINI. 150# RF ASME B16.5 71 INPUT SIGNAL 4-20 mA33 END EXTENSION/MATERIAL ASTM A105 carbon steel 72 TYPE ELECTRO-PNEUMATIC (HART) POSITIONER EXPLOSION34 FLOW DIRECTION YES 73 EExd PROTECTION ON INCR SIGNAL35 TYPE OF BONNET BOLTED 74 FIELD REVERSIBLE OUTPUT INCR/DECR36 LUB & ISO VALVE / LUBE 75 GAUGES Yes BYPASS Yes37 PACKING MATERIAL PTFE 76 CAM CHARACTERISTIC38 PACKING TYPE VTS 77 MFR & MODEL VTS SWITC39 VTS 78 TYPE - QTY - HES BONNET GASKET40 MFR & MODEL VTS 79 MFR & MODEL -General Control Valves. Prepared by: Gavhane D.V. 16
  17. 17. Contents of Control Valve:– Data Sheet . 41 TYPE VTS 80 CONTACTS/RATING - 42 SIZE RATED TRAVEL VTS VTS 81 ACTUATION POINTS - 43 CHARACTERISTIC VTS 82 44 BALANCED/UNBALANCED VTS 83 MATERIAL DIE CAST ALUMINIUM RATED CV VTS FL VTS XT VTS 84 FILTER SIZE < or = 25 Micron TRIM 45 AIR FILTER 46 PLUG/BALL/DISC MATERIAL F6 85 SET PRESSURE F6 SEAT HARD FACED WITH INTEGRAL PRESS. SEAT MATERIAL 86 50mm DIAL 47 STELLITE6. GAUGE 48 CAGE/GUIDE MATERIAL VTS 87 CONNECTION 1/2"NPT 49 STEM MATERIAL F6 88 MFR & MODEL VTS 50 89 51 NEC CLASS GR. DIV. 90 HYDRO PRESS. YES ACCESSORIES SPECIALS / 52 IEC ZONE GR. TEMP. CLASS CLASS I, ZONE 2 , GROUP IIA & T3 91 SEAT LEAKAGE TEST YES TESTS 53 92 CAPACITY TEST YES 54 93 55 94 NOTES : VTS-Vendor To SpecifyGeneral Control Valves. Prepared by: Gavhane D.V. 17
  18. 18. Globe Control Valve Construction. .General Control Valves. Prepared by: Gavhane D.V. 18
  19. 19. General Control Valve Classification. CONTROL VALVE LINEAR ROTARY MOTION MOTION Eccentric plugDiaphragm valve GLOBE VALVE Butterfly Gate valve Globe Ball Angle Three wayGeneral Control Valves. Prepared by: Gavhane D.V. 19
  20. 20. General Types of Control Valve. CONTROL VALVE TYPES VALVE TYPES BASED ON PLUG CONSTRUCTION ARE GLOBE VALVE BALL VALVE BUTTERFLY VALVEControl:- Linear & equal % Control:- Quick opening Control:- Linear & equal %Use:- Throttling Service, And linear. Uses:- Fully open / closed orFlow Regulation, Frequent Uses:- Fully open / closed Throttling services, FrequentOperation limited-throttling Operation, Minimal fluidApplication:- Liquid, Vapour, Application:- Most liquids Trapping in line.Gases, Corrosive Substances High temperature, slurries Application:-Liquids, gases,Slurries. Advantage:- High capacity Slurries, Liquids withAdvantage: Efficient throttling Low leakage and Maint. suspended Solids.Available in multiple ports. Tight sealing with low torque Advantage :- High CapacityAccurate Flow control. Disadvantage:- poor Good flow control, Low Press.Disadvantage: High pressure Throttling characteristics Drop, Low cost and Maint.Drop, more expensive. Prone to Cavitation Disadvantage:- High torque Required for control Prone to cavitation at lowerECENTRIC PLUG / CAMFLEX DIAPHRAGM KNIFE GATE Flows. General Control Valves. Prepared by: Gavhane D.V. 20
  21. 21. Eccentric Plug / Camflex Valve Construction. Side view of an eccentric plug valve Shown in partially open….. General Control Valves. Prepared by: Gavhane D.V. 21
  22. 22. Eccentric Disk/Ball/Knife Valve Construction Eccentric Disk Valve V-Notch Ball Valve Knife Gate Valve General Control Valves. Prepared by: Gavhane D.V. 22
  23. 23. Butterfly/Angle/Three Way Valve Construction General Control Valves. Prepared by: Gavhane D.V. 23
  24. 24. Diaphrgm Type Valve Construction. Seal over a seat ( Straight type) Weir type ( Saddle type)General Control Valves. Prepared by: Gavhane D.V. 24
  25. 25. General Types of Actuators . Actuator is the part of the valve that responds to the applied signal and causes modification of the fluid flow through stem & plug.TYPES OF ACTUATORS:1) Diaphragm Actuator Direct Acting Reverse Acting Size depends on output thrust required and supply air pressure available.2) Piston Actuator Use of high pressure air to 150 psig., eliminating the need of pressure regulator. Used where High & Fast Stroking Speed is required.3) Electro hydraulic Actuator: Electro-hydraulic Actuator is single unit contains Hydraulic Pump and Reservoir & Electric Motor. Ideal for isolated locations4) Manual Actuator Used where no auto control is requiredGeneral Control Valves. Prepared by: Gavhane D.V. 25
  26. 26. Direct – Acting Actuators .General Control Valves. Prepared by: Gavhane D.V. 26
  27. 27. Actuators Fail-Safe Requirements.Fail Safe is the action of the actuator by which the valve CLOSES (FC)or OPENS (FO) fully in case of air supply failure.General Control Valves. Prepared by: Gavhane D.V. 27
  28. 28. General Types of Bonnet & Accessories .Bonnet - Bonnet is a part of the valve body assembly through which the valve plug stem or rotary shaft moves.Types Of Bonnets Plain or Std Bonnet :-Operating Temp below 2000 c. Finned Bonnet :- Operating Temp above 2000 c or Equal. Extension Bonnet :- Operating Temp below 00 c or Equal. Extension Bonnet :- Operating Temp above 4500 c. Bellow Seal Bonnet :- where no stem leakage is tolerated For Toxic, Expensive Fluids.General Control Valve - Accessories •Positioners •Limit Switches •Solenoid Valves •Position Transmitters •Volume BoostersGeneral Control Valves. Prepared by: Gavhane D.V. 28
  29. 29. General Construction of Bonnet . Forged –Valve Finned Extension Bellow Seal Bonnet Bonnet Bonnet Bonnet ( Enviro Seal) Std./ plain BonnetGeneral Control Valves. Prepared by: Gavhane D.V. 29
  30. 30. Control valves Characteristics. PROCESS APPLICATION INHERANT CHARACTERISTICS PRESSURE LIQUIDS EQUAL % GAS (LOW FLOWS ) EQUAL % GAS (LARGE FLOWS) ΔPmax/Δpmin < 5 LINEAR ΔPmax/Δpmin > 5 EQUAL % Temperature Liquids & Gases EQUAL % Flow Load Changes EQUAL % Set point change LINEAR Level ΔPmax/Δpmin < 5 LINEAR ΔPmax/Δpmin > 5 EQUAL %General Control Valves. Prepared by: Gavhane D.V. 30
  31. 31. Control valves :- Interface PROCESS INTERFACE Process to provide process data to Instrument for specifying the valve Instrument to provide slected valve size to Process for incorporating in P&IDs Instrument to provide instrument air consumption figures for the valves to Process to decide air line & header sizes. PIPING INTERFACE Instrument to provide Face to Face Dimensions, End Connection Size & Rating, Actuator Height & Orientation, Envelope Dimensions (for 3-D Model), Weight, etc. Piping to provide location of control valves to Instrument for deciding instrument air manifolds. Piping to provide Pipe Material Specification to Instrument for specifying the valves.General Control Valves. Prepared by: Gavhane D.V. 31
  32. 32. Control valves Body Material.Frequently Used Valve Body Cast Materials Are: CARBON STEEL (ASTM A216 GR WCC) up to 4270 C CHROME MOLY STEEL (ASTM A217 GR WC9) up to 5930 C CARBON MOLY STEEL (ASTM A217 GR C5) up to 5930 C 304L STAINLESS STEEL (ASTM A351 GR CF3) up to 8160 C 316 STAINLESS STEEL (ASTM A351 GR CF8M) up to 8160 C CAST IRON (ASTM A126) up to 2320 CSpecial Materials Used Depending On The Process Requirements HASTEALLOY B HASTEALLOY C MONEL ALLOYGeneral Control Valves. Prepared by: Gavhane D.V. 32
  33. 33. Control valves Trim Material.Frequently Used Valve Trim Materials Are:• 302 SS : ASTM A 276 TYPE 302• 304 SS : ASTM A 276 TYPE 304• 316 SS : ASTM A 276 TYPE 316• 316 L SS : ASTM A 276 TYPE 316L• 410 SS : ASTM A 276 TYPE 410• 17-4 pH SS : ASTM A 461 GR 630 [High Tensile Strength, High Yield point, Hardened Material]• HASTEALLOY ``B’’ : ASTM A 335• HASTEALLOY ``C’’ : ASTM A 336General Control Valves. Prepared by: Gavhane D.V. 33
  34. 34. Control valves Codes and Standards.ANSI B 16.34 :• Covers Pressure, Temperature rating, Dimensions, Materials, NDT RequirementsANSI B 16.5 :• Covers design of flanges and flanged fittingsMSS SP 67 :• Covers design and test performance requirements of Butterfly valves and divides in to three leak classes.ANSI B 16.10:• Face to Face dimensionsANSI B 16.37: Hydrostatic testingLEAKAGE RATES AS PER ANSI/FCI 70-2 Formerly (ANSI B 16.104) for seat leak classes and testing procedures- FCIGeneral Control Valves. Prepared by: Gavhane D.V. 34
  35. 35. Vendor Design Documents- Sizing & SelectionStep # 1:- Define the systemExample :- The system is pumping water from one tank to another through apiping system total pressure drop is 150psi.The fluid is water at 700F.Design(maximum) flow of 150 gpm,operating flow rate of 110 gpm,and minimum flow rateof 25gpm. Pipe diameter is 3 inches. At 700F, water has has a specific gravity of1.0Key Variables:- Total pressure drop , design flow ,operating flow, minimum flow diameter, specific gravity.Step # 2:- Define Max. Allowable Pressure Drop For The Valve When defining the allowable pressure drop across the valve, you should firstinvestigate the pump.What is its maximum available head? Remember that thesystem pressure drop is limited by the pump. Essentially the Net Positive SuctionHead Available (NPSHA) minus the Net Positive Suction Head Required (NPSHR)is the maximum available pressure drop for the valve to use and this must not beexceeded or another pump will be needed. The usual rule of thumb is that a valveshould be designed to use 10-15% of the total pressure drop or 10 psi, whicheveris greater. For above example step#1 system, 10% of the total pressure drop is 15 psi whichis what well use as our allowable pressure drop when the valve is wide open (thepump is our system is easily capable of the additional pressure drop). General Control Valves. Prepared by: Gavhane D.V. 35
  36. 36. STEP #3: Calculate the valve characteristic General Control Valves. Prepared by: Gavhane D.V. 36
  37. 37. Step#4:-Preliminary Valve SelectionThe Cv value should be used as a guide in the valve selection, not a hardand fast rule. Some other considerations are: a. Never use a valve that is less than half the pipe size b. Avoid using the lower 10% and upper 20% of the valve stroke. The valve is much easier to control in the 10-80% stroke range.Before a valve can be selected, we have to decide what type of valve willbe used . For our case, well assume were using an equal percentage,globe valve . The valve chart for this type of valve is shown below. Thisis a typical chart that will be supplied by the manufacturer.For our case, it appears the 2 inch valve will work well for our Cv value atabout 80-85% of the stroke range. Notice that were not trying to squeezeour Cv into the 1 1/2 valve which would need to be at 100% stroke tohandle our maximum flow.General Control Valves. Prepared by: Gavhane D.V. 37
  38. 38. Typical Chart Supplied by Manufacturer.General Control Valves. Prepared by: Gavhane D.V. 38
  39. 39. Step# 5:-Check Cv & Stroke % at Min. FlowIf the stroke percentage falls below 10% at our minimum flow, a smallervalve may have to be used in some cases.Judgments plays role in many cases. For example, is your system morelikely to operate closer to the maximum flowrates more often than theminimum flowrates? Or is it more likely to operate near the minimum flow rate for extendedperiods of time. Its difficult to find the perfect valve, but you should findone that operates well most of the time. Lets check the valve weveselected for our system:General Control Valves. Prepared by: Gavhane D.V. 39
  40. 40. Step#6:Check Gain across Applicable Flow Rates• Gain is defined as:•• Now, at our three flowrates: Qmin = 25 gpm Qop = 110 gpm Qdes = 150 gpm we have corresponding Cv values of 6.5, 28, and 39. The corresponding stroke percentages are 35%, 73%, and 85% respectively. Now we construct the following table: Flow (gpm) Stroke (%) Change in (gpm) Change in Stroke (%) 25 35 110-25=85 73-35=38 110 73 150 85 150-110=40 85-73=12 Gain #1 = 85/38 = 2.2 Gain #2 = 40/12 = 3.3General Control Valves. Prepared by: Gavhane D.V. 40
  41. 41. General Control valve Gain.The difference between these values should be less than 50% of thehigher value.0.5 (3.3) = 1.65and 3.3 - 1.65 = 1.65. Since 2.2 is closer than 50%, there should beproblem with controlling the valve. Also note that the gain should neverbe less than 0.50.Turndown :- It is ratio of the calculated Cv at maximum condition to thecalculated Cv minimum.Rangeability :- It is ratio of Cv of the valve fully open to the minimum Cvat which it can control.The rangebility of the selected valve must exceed the turndownrequirements of the application.General Control Valves. Prepared by: Gavhane D.V. 41
  42. 42. General Control valves. Any Question ?General Control Valves. Prepared by: Gavhane D.V. 42

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