Definition. Control valves or proportional valves are power operated devices used to modify fluid flow or pressure rate in a process system.

Transcription

1 Control valve

2 Definition Control valves or proportional valves are power operated devices used to modify fluid flow or pressure rate in a process system. Common applications for on/off and throttling service : general purpose, process control, oil or fuel, sanitary, wastewater, water, irrigation, gas or air, steam, fire service, cryogenic, refrigeration, chemicals, and laboratory or medical.

3 Typical control valve Valve body Bonnet Packing box assembly Valve trim Yoke Actuator

4 Control Valve Classification

5 Linear Valve Features Rotary Valve Features Tortuous flow path Low recovery Can throttle small flow rates Offers variety of special trim design Suited to high-pressure application Usually flanged or threaded Separable bonnet Streamlined flow path High recovery More capacity Less packing wear Can handle slurry and abrasives Flangeless Integral bonnet High rangeability

6 Advantages of Rotary Valves Simple and lightweight Easy to automate Easy to maintain Quick opening Can be used in a variety of applications Available in multi-port configurations Applications of Rotary Valves Pharmaceutical applications Control applications Pneumatic conveying systems Dust collectors

7 Rotary shaft valves Butterfly valve Ball valve Rotary eccentric plug valve

8 Butterfly valve They are quick opening valves that consist of a metal circular disc which is fitted in a short flangeless pipe spool. They are normally used as throttling valves to control flow. They require minimum space for installation and provide high capacity with low pressure loss through the valve, another benefit is that,size for size, it has a large flow coefficient for producing a great flow.

9 Different types : Concentric butterfly valves Eccentric butterfly valves Resilient butterfly valve which has flexible rubber seat. Working pressure up to 1.6 Mpa High performance butterfly valve which is usually double eccentric in design. Working pressure up to 5.0 Mpa Tricentric butterfly valve which is usually with metal seated design. Working pressure up to 10.0 Mpa

10 drawbacks cavitation and choked flow occur easily in an application with a high-pressure drop. It has a poor-to-fair rangeability of 20 to 1 The increased hysteresis and dead band

11 Ball valve Ball valves are quarter-turn, straight through flow valves that have a round closure element with matching rounded seats that permit uniform sealing stress. they are used in situations where tight shut-off is required. They provide superior ease of operation and can maintain and regulate high volume, high pressure and high temperature flow. Most ball valves offer rugged construction providing for a long service life, and a comparably low cost.

12 Different types: There are three general types of ball valves: full port, standard port, and reduced port A full port ball valve has an oversized ball so that the hole in the ball is the same size as the pipeline resulting in lower friction loss. Flow is unrestricted, but the valve is larger. A standard port ball valve is usually less expensive, but has a smaller ball and a correspondingly smaller port. Flow through this valve is one pipe size smaller than the valve's pipe size resulting in slightly restricted flow. In reduced port ball valves, flow through the valve is two pipe sizes smaller than the valve's pipe size resulting in restricted flow.

13 Plug Valves In plug valves, the flow of fluid is controlled with the help of a rotary, cylindrical or tapered plug. When the plug is rotated, fluid flow is activated and a quarter turn in any direction can block the flow path completely. they are easy to install, simple to operate, support multi-port configuration and exhibit fast response. they are used in applications where valve cavities are undesirable and shut off at low pressure is required. Different type of plug valves include : lubricated, rotor, eccentric and non-lubricated plugs.

14 Lubricated Plug Valves Lubricated plug valve provide tight shutoff of fluids. Lubrication to the seal is retained with the help of a groove, and a hydraulic jacking force is provided to lift the plug, thereby the force required for rotary operation is reduced. Non Lubricated Plug Valves There are two types of non lubricated plug valves. Sleeved plug valves Fully lined plug valves Rotor Plug Valves Rotor plug valves are available in different sizes and materials. Teflon is used as the sealing material and the sleeve is rotated with the plug instead of rotating the plug within the sleeve.

15 Rotary Eccentric Plug Valves It offers high capacity and straight-through flow combined with tight shutoff. Eccentric plug valves are widely used in water and waste industry. They are available in a variety of materials.

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18 Control valve characteristics Quick opening Linear Modified linear Equal percentage Modified parabolic

19 Control valve accessories Some devices to perform a particular job in a control valve : Valve positioners Limit switches Solenoid valves Transducers Lock up valves Booster relays Capacity tanks Top mounted and side mounted handwheels Trip Valve

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21 Valve positioner What is a positioner? A controller that adjusts the instrument air in order to maintain the stem position at the specified position. How does it work? When a control signal differs from the valve actuator position, the valve positioner sends the necessary power to move the actuator until the correct position is reached.

22 Reasons To Use Positioners: Increase control system resolution: i.e. fine control. Minimize packing friction effects: i.e. high-temperature packing. Negate flow-induced reactions to higher pressure drops. Increase speed of response to a change in process. Allow split ranging. Overcome seating friction in rotary valves. Allow distances between controller and control valve. Allow wide range of flow variation: i.e. operate at less than 10% travel under normal conditions. Allow increased usage of 4-20 ma electronic signal. Increase fast venting (unloading) capability. Permit use of piston actuators. Facilitate operation when the higher number in the bench-set range is greater than 15 psig: i.e psig, 6-30 psig, etc.

23 Principle of operation : Pneumatic positioners A pneumatic signal (usually 3-15psig) is supplied to the positioner. The positioner translates this to a required valve position and supplies the valve actuator with the required air pressure to move the valve to the correct position Electric positioners send and receive electrical signals. There are three electric actuation types: single-phase and three-phase alternating current (AC), and direct current (DC) voltage. Electro-pneumatic positioners are used in electronic control loops to operate pneumatic diaphragm control valve actuators. the positioner receives a 4 to 20 ma DC input signal,and uses an I/P converter,nozzleflapper,and pneumatic relay.the output signal is applied directly to the actuator diaphragm. Digital or smart positioners use a microprocessor to position the valve actuator and monitor and record data.

24 Transducers A transducer is a device, usually electrical, electronic, or electromechanical, that converts one type of energy to another for the purpose of measurement or information transfer. In electronic control loops, the transducer receives a direct current input signal and uses a torque motor, nozzle-flapper,and pneumatic relay to convert the electric signal to a proportional pneumatic output signal.

25 Lockup valves Lockup valves used to hold valve in last position when air power fails. The lock-up valve closes the passage of air-flow piping by sensing the pressure of the main supply pressure when the pressure is lower than the setting pressure due to accidents and so forth.

26 Booster relays Booster relay provides high capacity air flow to the actuator of a valve. they are used to reduce lag time, resultin from long transmission lines, or when controller output capacity is insufficient for high demand devices, such as large diaphragm operators.

27 Hand wheel Handwheels may be supplied for manual operation of control valves for emergency use, during startup or in the event of air failure. They are used infrequently and primarily in critical services or when block and bypass valves are not provided.

28 Limit switches Limit switches may be mounted on valves to operate signal light for valve position indication, solenoid valve operation, alarms, or relays. Limit switches advantages : ruggedness, simple visible operation, ease of installation and reliability of operation.

29 Capacity tank Springless pneumatic actuators may stay in the last position on air failure but will more likely drift slowly to a closed or open position, depending on valve plug forces. When it is necessary to open or close a valve against line pressure, an airlock utilizing a capacity tank is used. This stored air pressure on the cushion loading side of the piston provides positive valve opening or closing regardless of the magnitude or direction of the forces involved when air supply failure occurs.

30 Solenoid valves A solenoid valve is a combination of two basic functional units : a valves and a solenoid. there are several types-direct action, internal pilot operated, external pilot operated, two way, three way and four way. The function of solenoid valve is to provide an on-off switching option in the system..

31 Direct solenoid actuation

32 Diaphragm operated Solenoid with forced lifting

33 Piston sea Pressure pilot valves

34 Trip Valve pressure-sensing trip valve is used for control applications where a specific valve/actuator action is required when supply pressure falls below a specific point. When supply pressure falls below the trip point the trip valve causes the actuator to fail up, lock in the last position, or fail down. When the supply pressure rises above the trip point, The trip valve can be top-mounted on a manifold, yoke-mounted, or bracket-mounted to match the application requirements.

35 Actuator Any device mounted on a valve that, in response to a signal, automatically moves the valve to the required position using an outside power source. There are three basic types of control signal inputs: milliampere, voltage, and pressure. There are several basic types of valve actuators : manual,electric, pneumatic and hydraulic.

36 Pneumatic valve actuator : Pneumatic valve actuator adjust valve position by converting air pressure into linear or rotary motion. Linear motion devices open and close gate, globe, diaphragm, pinch and angle-style valves with a sliding stem that controls the position of the closure element. Specifications for pneumatic valve actuators : actuation time control signal input acting type fail-safe position air supply pressure range operating temperature

37 Diaphragm actuator: A single-acting actuator that provides air pressure to one side of an elastometric barrier (diaphragm) to retract the actuator stem,which is cnnected to the closure element. It is used mainly with linear motion valves, but are suitable for rotary motion valves when used with some type of linear-to-rotary motion linkage.

38 Diaphragm actuator: Advantages Lowest Cost Can Throttle Without a Positioner Simplicity Inherent Fail-Safe Action Low Supply Pressure Required Adjustability Easily Maintained Disadvantages Large Size and Weight Limited Output Capability

39 piston actuators It uses a piston inside a pressure-retaining cylinder to provide double acting operation. with the double acting design air is supplied to both sides of the piston by a positioner Piston actuators are more resistant constructed than diaphragm actuators. They can be used with either linear or rotary valves. Operating pressures :7-10 bar ( psi )

40 The operation of piston cylinder actuators: As an air-to-close signal is sent from the controller to the positioner, the positioner sends air to the cylinder s upper chamber above the piston, while the positioner bleeds a comparable amount of air from the lower chamber below the piston. The changing pressures in these two chambers cause the piston to move downward. Subsequentle the actuator stem moves downwards does the valve stem.

41 Piston actuator Advantages High Torque Capability Compact Light weight Adaptable to High Ambient Temperature Fast Stroking Speed Relatively High Actuator Stiffness Disadvantages Fail-Safe Requires Accessories or Addition of Spring Positioner Required for Throttling Higher Cost High Supply Pressure Required

42 Rack-and pinion actuator Transfer the linear motion of piston cylinder actuators to rotary action. They are uses for actuating quarter-turn valves They are ideal for automating manually operated rotary valves: Compact Allow for field reversibility Provide adequate torque for most standard operations Easy to maintain and to understand

43 Vane actuator Uses a pie-shaped pressure-retaining housing and a rectangular piston (vane) to seal between the two pressure chambers. Only One Moving Part Advantages: Disadvantages Simple design with few moving parts applied to low pressure applications No hysterics Low cost Provide a leak path between air chamber Minimal weight Compact size

44 Features Only one moving part Double vane design Balanced and constant torque is applied directly to the valve stem, without any internal power loss, throughout the complete stroke. The most compact and efficient actuator design available.

45 Electric actuators Electric actuators mount on valves which, in response to a signal, automatically move to a desired position using an outside power source. Single-phase or three-phase AC or DC motors drive a combination of gears to generate the desired torque level. It consists of a reversible electric motor, control box, gearbox,limit switches and other controls The chief applications : in the power and nuclear power industries, where high pressure water systems require smooth, stable and slow valve stroking.

46 Electric actuators: Advantages Disadvantages Compactness High Cost Very High Stiffness Lack of Fail-Safe Action High Output Capability Limited Duty Cycle Slow Stroking Speed Electrohydraulic actuators : Advantages Disadvantages High Output Capability High Cost Fail-Safe Action Only With Accessories High Actuator Stiffness Complexity and Maintenance Difficulty Excellent Throttling Ability Large Size and weight Fast Stroking Speed

47 Hydraulic actuators Electrohydraulic actuators and hydraulic actuators convert fluid pressure into motion in response to a signal. They use an outside power source and receive signals that are measured in amperes, volts, or pressure. they use hydraulic fluid above and bellow a piston to position the valve. An electrohydraulic actuator uses a hydraulic actuator. An electrical signal feeds to an internal pumps which uses hydraulic fluid from a reservoir to feed hydraulic fluid above or bellow the piston.

48 Hand Wheel Actuators There are several circumstances where a hand wheel would be used. During plant start-up. During an emergency. On failure of pneumatic supply to the actuator. Where the control valve is not provided with a by-pass valve. Hand wheels can either be top mounted or side mounted.

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50 Codes and standards IEC Publications : IEC Electrical enclosures. ISA Publications : ISA S75.01 Flow equation for sizing of control valves ISA S75.03 Uniform face-to-face dimensions for flanged globe style control valve bodies American standards : ASME B31.3 Code for pressure piping Chemical plant and petroleum refinery piping ANSI B16-34 Hydraulic test for control valves ANSI / FCI 70-2 Control valve seat leakage API STD 598 Valve inspection and testing API 2000 Venting of atmospheric and low pressure storage tanks Miscellaneous standards : ISO Preparation of steel substrates before application of paints and related products

51 IEC Electrical enclosures Applies to the classification of degrees of protection provided by enclosures for electrical equipment with a rated voltage not exceeding 72,5 kv. Has the status of a basic safety publication in accordance with IEC Guide 104. It classifies the level of protection that electrical appliances provide against the intrusion of solid objects or dust, accidental contact, and water. The resulting ingress protection rating is identified by a code that consists of the letters IP followed by two digits and an optional letter. Where there is no protection rating with regard to one of the criteria, the digit is replaced with the letter X. For example, an electrical socket rated IP22 is protected against insertion of fingers and will not be damaged or become unsafe when exposed to vertically or nearly vertically dripping water. IP22 or IP2X are typical minimum requirements for the design of electrical accessories for in-door use.

52 ISA S75.01 Flow equation for sizing of control valves includes equations for predicting the flow coefficient of compressible and incompressible fluids through control valves. The equations for incompressible flow are based on standard hydrodynamic equations for Newtonian incompressible fluids. They are not intended for use when non-newtonian fluids, fluid mixtures, slurries, or liquid-solid conveyance systems are encountered. At very low ratios of pressure differential to absolute inlet pressure (DP/ P1), compressible fluids behave similarly to incompressible fluids. Under such conditions, the sizing equations for compressible flow can be traced to the standard hydrodynamic equations for Newtonian incompressible fluids. However, increasing values of DP/ P1 result in compressibility effects that require that the basic equations be modified by appropriate correction factors. The equations for compressible fluids are for use with gas or vapour and are not intended for use with multiphase streams such as gas-liquid, vapour-liquid or gas-solid mixtures.

53 ISA S75.03 Face to face dimensions for integral flanged globe-style control valve bodies This standard refers to valves, sizes ½ inch (15mm) through 16 inches(400mm), having top, top and bottom port or cage guiding. Purpose Aid users in their piping design by providing ANSI class 125 flat face, and ANSI classes 150,250,300 and 600 raised face,flat control valve dimensions, without giving special consideration of the equipment manufacturer to be used. Definition of pressure classes and flange dimensions, material identification, and cross reference information ANSI/ASME B , valves flanged, threaded, and welding end. ANSI/ASME B , cast iron pipe flanges and flanged fittings. ANSI/ASME B , pipe flanges and flanged fittings. ANSI/ASME B , face to face and end to end dimensions of valves. ANSI B Bronze pipe flanges and flanged fittings,class 150 and 300.

54 Face-to- face dimensions for flanged globe styles control valves

55 ASME B31.3 Code for pressure piping Chemical plant and petroleum refinery piping Rules for piping typically found in petroleum refineries; chemical, pharmaceutical, textile, paper, semiconductor, and cryogenic plants; and related processing plants and terminals. This code prescribes requirements for materials and components, design, fabrication, assembly, erection, examination, inspection, and testing of piping. This Code applies to piping for all fluids including: (1) raw, intermediate, and finished chemicals; (2) petroleum products; (3) gas, steam, air and water; (4) fluidized solids; (5) refrigerants; and (6) cryogenic fluids. Also included is piping which interconnects pieces or stages within a packaged equipment assembly

56 ANSI B16-34 Hydraulic test for control valves This Standard applies to new construction and covers pressure-temperature ratings, dimensions, tolerances, materials, nondestructive examination requirements, testing, and marking for cast, forged, and fabricated flanged, threaded, and welding end and wafer or flangeless valves of steel, nickel-base alloys, and other alloys. Alternative rules for NPS 2½ and smaller valves are given in Mandatory Appendix V. Standards and Specifications. Standards and specifications adopted by reference in this Standard and the names and addresses of the sponsoring organizations are shown in Mandatory Appendix VIII. It is not considered practical to refer to a specific edition of each of the standards and specifications in the individual clause references. Instead, the specific edition references are included in Mandatory Appendix VIII. Pressure Rating Designation. Class 400, an infrequently used flanged-end valve designation, is regarded as an intermediate class designation. Size. For NPS = 4, the related DN is: DN = 25 multiplied by the NPS number

57 ANSI/FCI 70-2 Control valve seat leakage This standard establishes six classes of seat leakage for control valves. Also defined are specific test procedures to determine the appropriate class. Included are classes commonly associated with double-port, double-seat or balanced single-port control valves with a piston ring seal or metal-to-metal seats; commercial unbalanced singleport, single-seat and balanced single-port valves with extra tight piston rings or other sealing means and metal-to-metal seats; valves for critical applications where the control valve may be required to be closed, without a blocking valve, for long period of time; and resilient seating control valves with "O" rings or similar gapless seals, among others.

58 API STD 598 Valve inspection and testing This standard covers inspection, examination, supplementary examinations, and pressure test requirements for resilient-seated, nonmetallic-seated (e.g., ceramic), and metal-tometal-seated valves of the gate, globe, plug, ball, check, and butterfly types. Resilient seats are considered to be: a. Soft seats, both solid and semi-solid grease type (e.g., lubricated plug). b. Combination soft and metal seats. c. Any other type valve designed to meet resilient seat leakage rates as specified in Table 5. API Std 598 supplements the API standards that reference it, but it may also be applied to other types of valves by agreement between the purchaser and the valve manufacturer. The inspection requirements pertain to examinations and testing by the manufacturer and any supplementary examinations that the purchaser may require at the valve manufacturer's plant. The test requirements cover both required and optional pressure tests at the valve manufacturer's plant. The following tests and examinations are specified in this standard: a. Shell test. b. Backseat test. c. Low-pressure closure test. d. High-pressure closure test. e. Visual examination of castings. f. High-pressure pneumatic shell test.

59 API 2000 Venting of atmospheric and low pressure storage tanks This standard covers the normal and emergency vapor venting requirements for aboveground liquid petroleum or petroleum products storage tanks and aboveground and underground refrigerated storage tanks designed for operation at pressures from vacuum through 15 pounds per square inch gauge (1.034 bar gauge). Discussed in this standard are the causes of overpressure or vacuum; determination of venting requirements; means of venting; selection, installation, and maintenance of venting devices; and testing and marking of relief devices.

60 ISO 8501 Preparation of steel substrates before application of paints and related products Preparation of steel substrates before application of paints and related products - Visual assessment of surface cleanliness - Informative supplement to Part 1: Representative photographic examples of the change of appearance imparted to steel when blast-cleaned with different abrasives. Identifies four levels of mill scale and rust that are commonly found on surfaces of uncoated steel. It also identifies certain degrees of visual cleanliness after surface preparation of uncoated steel surfaces and of steel surfaces after total removal of any previous coating. Are defined by written descriptions together with photographic examples. Is equivalent to Swedish Standard SS (88) which is used on a worldwide scale, contains 28 photographs and was published in the three ISO languages together with German, Dutch, Italian, Spanish, Portuguese, Arabic, Swedish, Japanese and Chinese. Specifies a series of preparation grades for steel surfaces after localized removal of previous paint coatings. Contains photographs showing examples of preparation grades. The various preparation grades are defined by written descriptions. Applicable to surfaces prepared for painting by methods such as blast-cleaning, hand- and power-tool cleaning, and machine abrading.

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