September 2012

Control Valves&

On-Off Valves

INDEXDefinition : ValveDefinition : Control Valves Parts of Control ValvesDefinition : On-Off Valves Need and Application of On-off valveTypes of Valve

• Globe Valve• Butterfly Valve• Ball Valve• Gate Valve•Eccentric Rotary plug

Characteristic Of Control ValvesActuatorAccessoriesLeakageCavitation & Flashing and their mitigationNoise and Noise ReductionHow to make valves fire-safe?ESD TriggersPerformance TestsPartial Stroke testStandards Relevant to Control ValvesStandards Relevant to On-Off ValvesTest and Certification Relevant to Control ValvesTest and Certification Relevant to On-off ValvesControl valve sizing

What is a Valve?

A valve is nothing but a restriction. A valve is a device that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways.

VALVE

Control valve On-off valve Motor Operated valve

A Control valve is a restriction which is capable of being modulated in a conduit that contains a flowing fluid

An ON-OFF/shut down valve (also referred to as Emergency shutdown valve, ESV, ESD, or ESDV) is an actuated valve designed to stop the flow of a fluid

Motor Operated valve is a valve where the Actuator Part is replaced by a motor. MOV are normally used for Larger Process lines where the Pneumatic pressure is not enough to provide required torque Valves movement. 

CONTROL VALVEThe most common final control element in the process control industries is the control valve.A Control valve is a restriction which is capable of being modulated in a conduit that contains a flowing fluid.Control valves are comprised of two major parts: the valve body, which contains all the mechanicalcomponents necessary to influence fluid flow; and the valve actuator, which provides the mechanicalpower necessary to move the components within the valve body.ISA S75.05 defined control valve as a power operated device which modifies the fluid flow rate in a process control system.It consists of a valve connected to an actuator mechanism that is capable of changing the position of a flow controlling element in the valve in response to a signal from a controlling system.Single-seat globe valve

• Valve Body- The main pressure boundary of the valve that also provides the pipe connecting ends and the fluid flow passageway, and supports the valve trim.

• Bonnet Assembly- The portion of the valve that contains the packing box and stem seal and also may guide the stem. It may also provide for the attachment of the actuator to the valve body. Typical bonnets are bolted, threaded, welded, pressure-sealed, or integral with the body.

• Trim- The internal components of a valve that modulate the flow of the controlled fluid. (In a globe valve typically, it would include plug, seat ring, cage, stem)

• Valve Plug- The movable part of the valve that is positioned in the flow path to modulate the rate of flow through the valve.

• Guide Bushing- The bushings fitted into the body, bonnet, bottom flange to guide the plug's post.

• Cage- A part of a valve trim, in a globe or angle body, that surrounds the closure member and whose flow passages may provide flow characterization and/or a seating surface. It may also provide stability, guiding, balance, and alignment.

• Seat Ring- A part of the valve body assembly that provides a seating surface for the closure member and may provide part of the flow control orifice.

• Seat- The line of contact between the closure member and its mating surface that establishes valve shutoff.

• Stem Connector- The device that connects the actuator stem to the valve stem.

• Yoke - The structure that rigidly connects the actuator power unit to the valve.

• Actuator- The purpose of a actuator is to provide the motive force to operate a valve mechanism.

• Positioner- a positioner is a device attached to an actuator that receives an electronic or pneumatic signal from a controller and compares that signal to the actuator’s position. If the signal and the actuator position differ, the positioner sends the necessary power, usually through compressed air to move the actuator until the correct position is reached.

ESD Operated/ON-OFF VALVES• An ON-OFF/shut down valve (also

referred to as Emergency shutdown valve, ESV, ESD, or ESDV) is an actuated valve designed to stop the flow of a hazardous fluid or external hydrocarbons (gases) upon the detection of a dangerous event.

• ESD/ESV valves provides defense against process miscreations.

• ESD / ESV valves are connected to Programmable Logic Controller (PLC) and together with sensors form the Safety Loop.

• They generally have a Tag Name starting as XV or XDV.

NEED AND APPLICATION• The lack of spring return capabilities on the different

electric actuator designs on the market and its dependence on the supply source to operate and react to any given situation know makes the users vulnerable to dangerous situations and potential environmental catastrophes.

• Also, with today's environmental standards and required practices, the need to have ESD capabilities becomes prevalent and changes the operational function of sectioning valves.

Need & Application (Contd.)• This provides protection against possible harm to people,

equipment or the environment.• Shutdown valves form part of a Safety instrumented

system (SIS).• Whenever sensors identify an abnormal dangerous

process situation, the PLC disconnects the power to ESD solenoid valve and the valve goes to desired fail safe mode by means of spring force (Fail Close/Fail Open).

• The process of providing automated safety protection upon the detection of a hazardous event is called Functional Safety.

VALVE

GLOBE BUTTERFLY BALL

SINGLE SEATED

DIAPHRAGM

DOUBLE SEATED ANGLE 3 WAY SEGMENTED / V-NOTCH FULL BORE

MIXINGDIVERTING

GATE

TYPES OF VALVES

ECCENTRICROTARY PLUG

Majorly the following kind of valves are used for Control valves:-Globe-Butterfly-Eccentric Rotary Plug -Segmented / V-Notch Ball

Majorly the following kind of valves are used for ON/OFF purposes-Ball Valve-Butterfly Valves-Gate Valves

GLOBE VALVE

Globe valves are named for their spherical body shape with the two halves of the body being separated by an

internal baffle.

Globe valves restrict the flow of fluid by altering the distance between a movable plug and a stationary

seat.

When the plug is fitted into the seat, it stops the flow of water. The plug can be left in any position from

completely closed, to completely open, depending on the required flow of fluid.

Size:• 1” to 16”; higher size available on request.

Application: • The globe valve design is one of the most popular valve designs

used in throttling service.• To control large range of process parameters, specially in

petrochemical, chemical, fertilizer, oil and gas, power, and other process plants.

• Globe valves are frequently used for control applications because of their suitability for throttling flow and the ease with which they can be given a specific 'characteristic', relating valve opening to flow.

Control Valve Body

GLOBE VALVE

Single seated globe valve

Flow through a single seat

Single-seated valves are the most widely used of the globe body patterns. There are good reasons for this:

• High flow capacity

• Tight shut off

• High rangeability

• They are available in a wide variety of configurations, including special-purpose trims.

• They are available with wide range of interchangeable trim size.

• They have good seating shut-off capability, are less subject to vibration due to reduced plug mass, and are generally easy to maintain.

Features:High flow capacity Tight shut offHigh rangeability. Valve flow rangeability, is the ratio of maximum rated flow to minimum

controllable flow. The governing parameter is Rated Cv.Higher Turndown, is the ratio between the valve’s maximum and minimum controllable flow

rate at stated operating pressures.Various type of trim e.g. contour, single stage, multi stage low noise, anti-cavitation trims, etc.Wide range of interchangeable trim size.Available characteristics - Quick opening, Linear & Equal percentage. The valve trim consists

of the internal parts contained within the body and wetted by the process fluid. The main components are the plug and stem and the seat rings. The trim design also serves to determine the inherent flow characteristics of the valve.

Valve plug shapes to produce the three common flow characteristics:

equal percentage, linear, and quick opening.

APPLICATION:• Angle valves are typically used in high pressure drop

applications and for erosive service where impingement of solid particles is to be avoided. At high pressure drops the velocity would be very high, therefore depending on actual downstream velocities, these applications can require a larger pipe size than the valve.

• Where process fluid contains solid particles.• Corrosive or high viscous fluid which shall solidify at room

temperature, because the downwards output port does not allow the solidified material to stay inside valve body.

Angle valve

Angle valve

Typical Features:1. High Flow Capacity

2. Tight Shut-off

Three-way valves are another form of specialized globe valve body configuration that serve two basic services:

1. Mixing service for the combination of two fluid streams passing to a common outlet port.2. Diverting service for separating a common inlet port into two outlet ports. Three way valves are ideal for mixing two separate flows by having two inlets and one

outlet, or dividing a flow into two proportional parts by having one common inlet and two outlets.

3 Way valve

Butterfly valveThe rotary valves such as butterfly, ball, and plug valves were once considered to be only on/off valves. In recent decades the rotary valves in general and the butterfly design in particular have been used more and more as throttling control valves.

ADVANTAGE: Relative to the traditional globe control valve, the butterfly valves have the advantages of lower cost and weight, two to three times the flow capacity of globe valves fire-safe designs, tight shut-off and low stem leakage. Little resistance to flow (allows smooth flow).Optimal for automated operation with a low operating torque and 90 degrees operating angle.

DISADVANTAGE: When used for throttling service, some of their disadvantages are a direct consequence of the above advantages. Their high-capacity design results in either using oversized valves or having small valves mounted in large pipes. If small valves are used, this means substantial waste of pumping energy caused by the reducer pressure drops.

The vane positions of butterfly valve when closed, throttling, or open.

Butterfly Valves

Lug Type Double Flanged TypeWafer Type

• Available in following designs

Butterfly valves designed for tight shut-off (TSO) fall into two categories:• One is the valve that is provided with an elastomer or plastic liner.• The other tight shut-off design is the HPBV with the cammed disc and a separate

seal ring clamped into the body

HPBV Type

Designs on basis of connection High Performance design

Butterfly Valves (Contd)

ZERO OFFSET •Concentric valve (zero offset).•Disc rotates around the centre axis allowing for a potential 360 rotation.•Sealing is achieved by the Disc deforming the soft seal resulting in full friction through the full operating cycle.

DOUBLE OFFSET

• The shaft is offset from the centre line of the disc seat and body seal (offset one), and the centre line of the

bore (offset two).

TRIPLE OFFSET

• The third offset is the geometry design of the sealing components not the shaft position. The sealing

components are each machined into an offset conical profile resulting in a right angled cone.

• This ensures friction free stroking throughout its operating cycle. Contact is only made at the final point

of closure with the 90° angle acting as a mechanical stop; resulting in no over - travel of the disc seat.

Ball valveA ball valve is a valve with a spherical disc/ball, the part of the valve which controls the flow through it. The sphere has a hole, or port, through the middle so that when the port is in line with both ends of the valve, flow will occur. When the valve is closed, the hole is perpendicular to the ends of the valve, and flow is blocked Ball valves are straight-through flow valves which provide positive shut off with minimal pressure drop and flow turbulence. The barrier to flow is a ball which is rotated 90 degrees to the direction of flow.

The ball valve is very reliable. It can be engineered to withstand HIGH pressure. It takes a quarter turn to open or close them fully. It is widely used for ON-Off/shutdown applications and in special cases for regulating services.

Ball Valves• Ball valves are durable and usually work to achieve perfect shutoff even after

years of disuse.• Used in steam, water, oil, gas, air, corrosive fluids, and can also handle slurries

and dusty dry fluids.• Abrasive and fibrous materials can damage the seats and the ball surface.• Their tight shut-off characteristics correspond to ANSI Class IV and VI.• The fire-safe design of ball valves can be certified to API-607, which specifies the

types of secondary seats that are acceptable to control the leaking of flammable fluids, when the primary seat (usually PTFE) sublimes during fire.

Features:– High flow capacity.– Metal to metal trim, soft seated trim. – Tight shut off (Leakage - ANSI class IV) with soft seat.– Minimum obstruction for the flowing media.– “O” ball and “V” notch construction available. The V-notch

ball provides nearly equal percentage flow characteristic. The V-shaped notch cut into the opening lip of the ball provides a narrower area for fluid flow at low opening angles, providing more precise flow control than a plain-bore ball valve. Also known as segmented ball valve.

V-Notch Ball Design

Types Of Ball ValveFloat ball valve:• Floating ball in the ball valves means a ball that is free to

“float” between the seat rings. The ball is held on two seat rings. In general we can also say that the floating ball valves have float ball and fixed seat.

• Floating ball valves by its construction use an upstream pressure to push the ball against its seat.

• In general practice, the floating ball valve is used at low pressure application due to its seat limitation (at high pressure the ball is leaning to push and broke the seat). Floating ball valves also used at small size only due to its difficulties to align to seat if the ball size is big.

• In general practice for piping application, for below 3” size at 150 or 300 ANSI class should be use floating ball valves.

Types Of Ball Valve (Contd.)Trunnion Mounted:• Trunnion mounted ball in the ball valves means the

ball is held by a fixed vertical axis.• In trunnion mounted, the upstream pressure is

absorbed by a bearing and the tightness is achieved by a spring inside the seat. This seat is pushed by a spring to have a tighten sealing.

• The trunnion mounted is capable to use at high pressure application and large size ball valves without major problem.

• At high pressure and large size application the trunnion mounted is superior to the floating ball valves type.

• For sizes 3” and above (150 or 300 ANSI class) or at ANSI class 600 and above all size, it shall be use of trunnion mounted ball valves.

Floating Ball v/s Trunnion MountedIn general application the actuated ball valves used for shutdown valve or blow down is categorized as a critical application. It serves a Safety Instrumented System (SIS) that has a certain requirement of Safety Integrity Level (SIL) • Due to its critical role, the ESD ball valves are usually trunnion mounted instead of floating type. • Torque and the upstream pressure acting on the seat is the main point for choice the type. If the pressure

acting on the seat is high, the stem of the floating type can not bear the pressure and much of it will act on the Seal seat ,This will made the seat broken ,also when we close or open the valves, the torque will be high. We may need to choose a big actuator.

• In Trunnion type, the ball is fixed and can reduce some torque. It also protects the seat when the valve is closed and high upstream pressure act on the ball.

• But it also depends on the manufacturer capabilities. Sometimes manufacturer capabilities to fabricate a trunnion mounted ball valves is limited to 2” smallest size. In this case, the floating type is unavoidable.

• So as a conclusion, instrument ball valves used as shutdown or blow down application shall be trunnion mounted type and the use of floating type is only acceptable if the use of trunnion mounted type isn’t feasible.

The KNIFE GATE-TYPE : It works by changing the process fluid’s flow rate by sliding a plate past a stationary hole.

• Knife Gate valves are relatively inexpensive, have high capacity, and are suited for slurry and dirty services.

• On the other hand they have poor control characteristics, do not provide tight shut-off, and are not suited for corrosive services.

• It is a form of “guillotine”-type gate valve and is much used due to its non-plugging body design.

• Non-abrasive slurry services such as in the pulp & paper industry.

• For large diameter water services as found in waste water systems.

Gate valve

POSITIONED-DISC VALVES: Rotation of a movable disc with two holes, which if rotated can progressively cover two holes in the stationary disc, can successfully throttle flow.• The positioned sliding disc designs are ideal for high-pressure

(up to 10,000 PSIG), cavitating, abrasive, or erosive services, but are relatively expensive and are not suited for sludge, slurry, viscous, or fibrous services.

KNIFE GATE-TYPE

POSITIONED-DISC VALVES

Slab-type knife gate

Guillotine-type knife Gate Valve:Slide gate guillotine valves are used on low pressure flue gas or airflow service

as a block off valve. These valves are available in bonneted or bonnetless

design.

• The eccentric plug rotary control valve features an eccentrically mounted plug or ball, which combines rotary valve efficiency with globe valve ruggedness..

• Excellent Flow Characteristic• High Capacity• One-Piece Body• Rugged Construction• Reliable Performance• The High Rangeability• One of the main advantages of the rotary plug valve is its free passage. Due to the flow restrictor which

moves crossways to the flow, the plug does not directly bears the brut of the flowing fluid. This confers a special advantage on abrasive or adhesive media.

Eccentric Rotary Plug valve

Sr. No. Type of VALVE Area of Application1 1. Butterfly Valves

2. High Performance Butterfly Valves

1.a. Control & Isolation (on-off) of Air, Gas, Toxic Chemicals, Acids & Alkalies Etc.

1.b. Used for control application at higher valve sizes instead of globe valves

1.c. For corrosive services, where body lining of globe valves becomes economically unattractive.

2. Control & Isolation of High Temperature, High Pressure Fluids Etc.

2 Ball Valves 1. Isolation (on-off) of Fluids at Moderate pressure & Temp.2. Quick Opening

3 Diaphragm Valves 1. On/Off applications in slurry service.2. Glandless Valve Hence Most Suitable for Vacuum Application

4 Knife Edge Gate Valves 1. Isolation Of Slurry & Pulp Applications2. On-Off application

5 1. Globe valve2. Below Sealed Globe

Valves

1. To control large range of process parameters, specially in petrochemical, chemical, fertilizer, oil and gas, power, and other process plants

2. Control & Isolation (on-off) of Highly Toxic Fluids & Zero Leakage to Atmosphere.

Normally classified three types of characteristics

• Quick opening• Linear• Equal percentage• Square root• Modified parabolic• Hyperbolic

% Lift0

20

40

60

80

100

20 40 60 80 100

Quick Opening

% Flow Linear

Equal Percentage

Characteristic : The flow characteristic of a control valve is the relationship between the flow rate through the valve and the valve travel, as the travel is varied from 0 to 100%.

Control Valves Characteristic

• Quick Opening An inherent flow characteristic in which there is maximum flow with minimum travel.Quick opening valves are typically used for ON-OFF service. Use for processes, where “instantly” large flow is needed.

• Linear The rate of change of flow is same to the rate of change of valve travel.Linear characteristics are provided for most level control loops, and loops where the measurement is linear and the variation in the pressure drop across the control valve is small.

• Equal percentage • Provides equal percentage increases in rate of flow for equal increments of plug movement.• The equal percentage valve offers an advantage over the linear valve at low flow rates. Consider, at a 10% flow

rate of 1 m/h, the linear valve only lifts roughly 4%, whereas the equal percentage valve lifts roughly 20%. Although the orifice pass area of both valves will be exactly the same, the shape of the equal percentage valve plug means that it operates further away from its seat, reducing the risk of impact damage between the valve plug and seat due to quick reductions in load at low flow rates.

• Higher rangeability.

Selecting a valve with the correct flow characteristic (the relationship between valve opening and flow capacity) is very important. Actually, a control valve has two characteristics, an INHERENT CHARACTERISTIC and an INSTALLED CHARACTERISTIC.

The inherent characteristic of a valve is the characteristic published by the manufacturer, based on tests performed in a system where great care is taken to ensure that the pressure drop across the test valve is held constant at all valve openings and flow rates. The inherent characteristic, therefore, represents the relationship between valve flow capacity and valve opening when there are no system effects involved.

The inherent characteristic can be determined in a flow-test lab with a constant, pressure drop, but what if the pressure drop is not constant as is quite often the case? The answer is because of the installed characteristic. The Installed characteristics of a control valve refer to the relationship between the flowrate through the valve and the valve travel, as the valve is opened from its closed position to various degree of opening, when the pressure drop across the valve varies.

Note that, the pressure drop across the valve (DPV) varies in most actual installation, influenced also by various pressure-reducing devices in series with the control valve, such as the pipe length, pipe fittings and various types of valves, flowmeter and process equipment.

NOTE: In actual flow conditions (installed characteristics) the equal % moves toward linear and linear characteristics to quick opening characteristics. Quick opening characteristics is undesirable for throttling applications since in dynamic condition it moves toward on-off characteristics.

Type:• Pneumatic - Valve is operated by pneumatic supply on the actuator. Pneumatic valve actuators respond

to an air signal by moving the valve trim into a corresponding throttling position. Pneumatic actuators use air pressure pushing against either a flexible diaphragm or a piston to move a valve mechanism.

- Diaphragm- Piston operated

• Single acting• Double acting

• Electric - Valve is operated by electrical motor which is couple to the valve shaft through gear box. Electric motors have long been used to actuate large valves, especially valves operated as on/off (“shutoff”) devices.

• Hydraulic-Hydraulic actuators use liquid pressure rather than gas pressure to move the valve mechanism. Nearly all hydraulic actuator designs use a piston rather than a diaphragm to convert fluid pressure into mechanical force.

• As shutdown valves form part of a SIS it is necessary to operate the valve by means of an actuator.• Scotch & Yoke / Rack & Pinion are the most commonly used mechanisms in on-off rotary valve

actuators because of their high torque production.

ACTUATORS• Definition: A pneumatic, hydraulic, or electrically powered device that supplies force and motion to position a

valve’s closure member at or between the open or closed position. Thus, an actuator is any device that causes the valve stem to move.The purpose of a control valve actuator is to provide the motive force to operate a valve mechanism.It may be a manually positioned device, such as a handwheel or lever.

Piston actuatorsLinear piston actuators provide longer strokes and can operate at higher air pressures than can the spring/diaphragm actuators. Compressed air is applied to a solid piston contained within a solid cylinder. Piston actuators can be single acting or double acting.Piston Actuators are used with on-off valves and also with large size valves which require longer stroke.

Diaphragm actuatorsDiaphragm actuators have compressed air applied to a flexible membrane called the diaphragm. Figure shows a rolling diaphragm where the effective diaphragm area is virtually constant throughout the actuator stroke. • The popularity of the spring/diaphragm actuator is due to its low

cost, its relatively high thrust at low air supply pressures, and its availability with “fail-safe” springs.

Spring diaphragm actuators are the most widely recognized and used by control valve suppliers.Simplistic design ,few moving parts, and easy to maintain.

Adobe Acrobat 7.0 Document

Diaphragm actuator

Scotch & Yoke / Rack & Pinion: They are the most commonly used mechanisms in on-off rotary valve actuators because of their high torque production

• In addition to the fluid type, actuators also vary in the manner in which the energy is stored to operate the valve on demand as follows:

Single-acting cylinder/ Spring Return - Energy is stored by means of a compressed spring

Double-acting cylinder - Energy is stored using a volume of compressed fluid

• The type of actuation required also depends upon the application, site facilities and also the physical space available.

• Although the majority of actuators used for shutdown valves are of the spring return type due to the fail safe nature of spring return systems.

Rack & Pinion Actuator

The valve application engineer must choose between the two readily available fail-safe schemes for control valves, either fail open or fail closed. This means "what position will the valve move to should the supply air or control signal to the valve falls away". This is important to safe guard the process at various places so some valves will be fail open and some fail close.

• Fail open- A condition wherein the valve closure member moves to an open position when the actuating energy source fails.

• Fail close- A condition wherein the valve closure member moves to a closed position when the actuating energy source fails.

• Fail safe- A characteristic of a particular valve and its actuator that upon loss of actuating energy supply will cause a valve closure member to be fully closed, fully open, or remain in the last position, whichever position is defined as necessary to protect the process.

• Fail lock- Pneumatic lock-up systems are used with control valves to lock in existing actuator loading pressure in the event of supply pressure failure. This is done by installing a "lockup valve" inline with the pneumatic actuator's air line trapping air inside the actuator under "fail" conditions. When the lockup valve shuts, no air can enter or exit the control valve's actuator, which makes the control valve hold its position.

In valves without a positioner, when the valve is given a command to open to a certain point, there is no feedback to verify that the valve has opened to that position. With a valve positioner, the command is given and the valve positioner reads the opening, verifying the position and readjusting until it gets it to the exact position needed. This allows for great precision in the valve adjustmentBy definition, a positioner is a device attached to an actuator that receives an electronic or pneumatic signal from a controller and compares that signal to the actuator’s position. If the signal and the actuator position differ, the positioner sends the necessary power—usually through compressed air—to move the actuator until the correct position is reached.

Positioner

A positioner ensures that for a given input signal, the valve will always attempt to maintain the same position regardless of changes in valve differential pressure, stem friction, diaphragm hysteresis and so on.

A positioner may be used as a signal amplifier or booster. It accepts a low pressure air control signal and, by using its own higher pressure input, multiplies this to provide a higher pressure output air signal to the actuator diaphragm, if required, to ensure that the valve reaches the desired position.

There are four basic valve positioner types: pneumatic, electronic, electro-pneumatic and digital. • Pneumatic valve postioners communicate with air. • Electric valve positioners use electric signals; single or three-phase AC or DC current is used. • Electro-pneumatic valve positioners take an electric signal and convert it to a pneumatic (air) signal. • Digital valve actuators use a microprocessor to monitor the valve accurately.

A frequently asked question is, 'When should a positioner be fitted?

A positioner should be considered in the following circumstances:

1. When accurate valve positioning is required. 2. To speed up the valve response. The positioner uses higher pressure and greater air flow to adjust

the valve position. 3. To increase the pressure that a particular actuator and valve can close against. (To act as an

amplifier). 4. Where friction in the valve (especially the packing) would cause unacceptable hysteresis. 5. Where varying differential pressures within the fluid would cause the plug position to vary.

'When should a positioner NOT be fitted?

1. A positioner should not be used if the process is too fast.

2. Another is a small valve with a relatively large actuator and good available force

The response of a “fast” process is better without a positioner,

LIMIT SWITCHThe indication from the valve limit switches that tells the operator and the

logic when the valve is fully open or fully closed.Switches are installed on electric motor-driven valves to open the circuit and stop driving the motor when the valve is at its limit (fully open or closed). The

name “limit switch” is also used to describe switches installed to signal when a valve is at or beyond a predetermined position.

For hazardous area, switch shall be either intrinsically safe or switch mounted in ex-proofing housing.

When specifying the limit switches, one should specify the required contact ratings, the contact configurations (SPDT, DPDT, and so on), and the type of housing required. Typical choices include weatherproof, explosion proof etc.

TYPES OF LIMIT SWITCHES USED:

SENSOR TARGET SENSOR DISTANCE SWITCH RATE

ENVIRONMENTAL SENSITIVITIES

ADVANTAGES DISADVANTAGES

Limit Switch Any Physical Contact required

3Hz Temperature, Moisture

Simple, Inexpensive Physical Contact, Arcing

Photo-electric

Opaque 0.1-50mm 100-1000Hz

Dust, Dirt, Ambient Light

Good Resolution

UltrasonicType

Non-porous, large

30mm-10m 50Hz Noise, Air Motion Poor Resolution

InductiveType

Conductive Material

Ferrous-50mm, Non-ferrous- less

300-5000Hz

Other nearby sensors Usually fails ON, good Resolution

CapacitiveType

Most liquids, solids

30mm 500Hz Humidity, temperature

Complex ckt, False triggering

INDUCTIVE TYPE

Solenoid Valves: Solenoid valves are often found in applications in which a

control valve under certain conditions must be quickly driven to the fail position

• The solenoid valve as a control valve accessory is used (1) To operate on/off pneumatic actuators (2) To interrupt the action of modulating valves by

switching air or hydraulic pressures.• In order for the system to shut down (valve to close) in case

of loss of power or emergence of an unsafe condition, it is desirable for the solenoid valve to be continuously energized during normal operation. This will guarantee that any failure, loss of power, or a broken wire will cause a fail-safe action.

• We can use brass, aluminum, or even 316 SS for the body material since all of this material is compatible with the instrument air.

• Though solenoid valve material is 316LSS as minimum or per project specifications as it is corrosion resistant.

2/2 way normally closed solenoid valve

3/2 way normally closed solenoid valve

SOLENOID VALVE COIL INSULATION• When the solenoid valve is energized, there is some heat energy generated by this conductors

winding. Since the conductors winding dissipate some heat energy, the insulation must endure this heat.

• If the insulation isn’t strong enough to endure against the heat, then it will melt or burnt. Furthermore the broken insulation will cause a short circuit and the solenoid will fail to operate.

• In general, the insulation of solenoid valve coil can be made from paper, polyester, polyurethane, nylon, etc.

• Solenoid Valve Coil Insulation Class Maximum Temperature B 130 deg C F 155 deg C H 180 deg C • In general application for shutdown valve triggering, the vendor will provide the temperature rise

data of the solenoid at full load (energized). With this temperature rise data, they will provide standard insulation class and state the maximum ambient temperature for that solenoid valves.

• For example, the solenoid valves have an inherent temperature rise 900 C at full load. By providing insulation class F (max temperature 1550 C), it will be allowed to operate at 650 C ambient temperature. In most application, the ambient temperature will not exceed 400 C, therefore it will have 250 C extra thermal capabilities. This extra thermal capability can be used to extend the solenoid valve life expectancy.

Supply pressure regulators, commonly called airsets, reduce plant air supply to valve positioners and other control equipment.

They perform two critical functions: providing a constant air supply pressure to the instrument or valve, and filtering the instrument air, that is to remove moisture, oil, and all particles that are 5 μ or larger.

The pressure-reducing function is essential to a plant’s performance and safety. Most plant instrument air systems operate at pressures of 100 psi (6.9 bar) or higher, while most control valves and other instruments are designed to run at much lower air supply pressures—as low as 20 psi (1.4 bar) in some cases.Exceeding the rated supply pressure can lead to early failure, mechanical damage, system shutdowns and potentially unsafe conditions.

It is often purchased with the valve, mounted, and piped.An air set must be used when the pressure rating of the actuator or positioner is lower than the air supply pressure.

General filter material: Sintered Polypropylene, Sintered Polyethylene

Air filter regulator

Air Filter Regulator

Hand-wheel• Hand wheel may be supplied for manual operation of control valves for

emergency use, during start up or in the event of the air failure.

• They are used infrequently & primarily in critical services or when block & bypass valves are not provided.

LeakageThis is the basically the fluid which passes through the valve when the valve is fully closed. So this

leakage shall depend on the contact of the valve plug seat with the seating force applied for holding the plug over the seat.

Leakage Class

Maximum Allowable

Test Medium Test Pressures

II 0.5% of rated valve capacity air or water 45-60 PSIG or maximum

difference pressure, whichever is less

III 0.1% of rated valve capacity air or water 45-60 PSIG or maximum

difference pressure, whichever is less

IV 0.01% of rated valve capacity air or water 45-60 PSIG or maximum

difference pressure, whichever is less

V 0.0005 ml per min. per inch

orifice diameter (seat diameter) per psi

differential water 100 PSI minimum or maximum

difference pressure

VI Refer to table adjacent air or

nitrogen

50 PSI or maximum difference pressure, whichever is

lower

Seat Leakage According to ANSI B16.104-1976 (FCI 70-2)

Nominal Port Diameter ml Per Minute Bubbles Per

Minute

1.00 0.15 1.00

1-1/2 0.30 2.00

2.00 0.45 3.00

2-1/2 0.60 4.00

3.00 0.90 6.00

4.00 1.70 11.00

6.00 4.00 27.00

8.00 6.75 45.00

Class I. Identical to Class II, III, and IV in construction and design intent, but no actual shop test is made.

Class II. Intended for double-port or balanced singe-port valves with a metal piston ring seal and metal-to-metal seats. Air or water at 45 to 60 psig is the test fluid. Allowable leakage is 0.5% of the rated full open capacity.

Class III. Intended for the same types of valves as in Class II. Allowable leakage is limited to 0.1% of rated valve capacity.

Class IV. Intended for single-port and balanced single-port valves with extra-tight piston seals and metal-to-metal seats. Leakage rate is limited to 0.01% of rated valve capacity.

Class V. Intended for the same types of valves as Class IV. The test fluid is water at 100 psig or operating pressure. Leakage allowed is limited to 5 X 10 ml per minute per inch of orifice diameter per psi differential.

Class VI. Intended for resilient-seating valves. The test fluid is air or nitrogen. Pressure is the lesser of 50 psig or operating pressure. The leakage limit depends on valve size and ranges from 0.15 to 6.75 ml per minute for valve sizes 1 through 8 inches.

CLASS IV is also known as metal to metal. It is the kind of leakage rate you can expect from a valve with a metal plug and metal seat.

CLASS Vl is known as a soft seat classification. Soft Seat Valves are those where either the plug or seat or both are made from some kind of composition material such as Teflon or similar.

Flow direction

Pipe

Flow restriction

Inlet pressure

Outlet pressureVapor pressure

Vena Contracta pressure

p1

p2pvpvc

Flashing & Cavitation Phenomena

FlashingIf the pressure at the vena contracta drops below the vapour pressure of

the liquid, bubbles will form in the flowing stream. If the pressure downstream remains below the vapour pressure, the bubbles will remain and the process is said to have “flashed.” Flashing can produce erosion damage, normally at the point of highest velocity at or near the seat line of the valve plug and the seat ring.

When the liquid flashes into vapour, there is a increase in volume, resulting in the increase in the velocity of the fluid. Hence this high velocity will erode the surface.

Flashing damage can be identified as smooth polished appearance of erode surface. It is usually at or near seat line of the valve plug and seat. Flashing damage is marked by shiny, smooth gouges in material.

When a liquid flashes into vapor, there is a large increase in volume. In this circumstance, the piping downstream of a valve needs to be much larger than the inlet piping in order to keep the velocity of the two-phase stream low enough to prevent erosion. The ideal valve to use for such applications is an angle valve with an oversized outlet connection.To protect the valve the valve material must be hardened. If there is 100% flashing then the valve should be slightly oversized in order to accommodate the increased volume and keep velocity of vapour low enough.

CavitationCavitation is said to have occurred if the downstream pressure

recovery is sufficient to go above the vapour pressure, collapsing the bubbles, releasing energy, making noise, and causing erosion.

Choked cavitation is the point where the vaporization of the fluid reaches sonic velocity in the valve port and limits the flow through the valve.

Cavitation damage can be identified as rough and pitted surface. Cavitation damage may extend to the downstream pipeline if that is where the pressure recovery occurs.

• Destruction is due to the implosions( the bubbles collapse ) that generate the extremely high-pressure shock waves in the substantially non-compressible stream. Cavitation is usually coupled with vibration and a sound like rock fragments or gravel flowing through the valve.

Cavitation Damage

In order to ELIMINATE CAVITATION: Install two or more control valves in series as pressure drop is distributed.

The more treacherous the flow path through a particular valve, the less likelihood exists for cavitation. Inversely, the valves most likely to cavitate are the high recovery valves (ball, butterfly, gate) as the flow path is less complicated.

Control valve designs that are less likely to cavitate are ones having multipath and multiturn flow paths.

Labyrinth-type valves avoid cavitation by a very large series of right-angle turns with negligible pressure recovery at each turn..

The multistep / multistage valves can avoid cavitation by replacing a single and deep vena contracta with several small vena contracta points as the pressure drop is distributed.

Multi-Grooved Cascade trim for non-compressible fluid applications. There are 8~9 grooves designs available depending on pressure drop and potential for cavitation. The fluid passes through the flow path generated by incorporating angled flats onto the surface of the plug. The pressure drop progressively reduces as it passes through the grooves of the trim.

By proper material selection. Such as Like SS316 / COLMONOY 6 coating/ STELLITE coating / ALLOY 6 which are likely to survive longer.

The multistep valves

MULTI PATH TRIM SECTION

Noise Theory

A random mixture of sound and pressure waves of various amplitude and frequency, which people do not like.Unit of noise – dBA (Decibels) = 20Log (Existing sound pressure level / .0002 micro bar).Typical noise limit is 85 dBA before some kind of action is required.

Source of valve noise

• Mechanical noise – It produces high mechanical stress- fatigue failure of vibration part. Mechanical noise can be reduced by improved design to suppress vibration by good support and rugged construction.

Vibration of valve components – it is due to lateral movement of valve plug against the guide surface. The sound level produce will normally have frequency less than1500 Hz and is known as metallic rattling.

• Hydrodynamic noise – It is due to cavitation and flashing. It is because of collapsing of vapour bubbles.

• Aerodynamic Noise – Aerodynamic noise is generated by the turbulence created in the flow of vapor, gas, or steam as the fluid passes through a control valve

• Noise control– Path treatment

• Insulation of pipe : Thermal Insulation :3 to 5 dBA of noise attenuation per inch. Acoustical Insulation: 8 to 10 dBA per inch

• Heavy duty pipe• Silencer:

In-line silencers: Absorb sound energy Applied when source treatment is insufficient

Cost effectively provide up to 25dBA attenuation

StandardSchedule40 Pipe

110 dBA

Schedule80 Pipe

106 dBA

AcousticInsulation(2-inches)

96 dBA

StandardSchedule40 Pipe

110 dBA

Silencer

85 dBA

StandardSchedule40 Pipe

85 dBA

• Noise control– Source treatment

• Prevents noise at its source,• Minimizes turbulence.

– Staging pressure drop through use of diffusers– Dividing up flow path through slots or drilled holes

Example:•Low Noise Trim – Cage style (e.g. Whisper trim)

Whisper Flo (Noise reduction up to 10 dBA)Whisper I (Noise reduction up to 18 dBA)Whisper III (Noise reduction up to 30 dBA)

•By In line diffuser•By whisper disk

Noise reduction trim

HOW TO MAKE VALVES FIRE-SAFE?• There are also two methods to achieve a fire-safe design, by using a fire-proof

component or by using a non fire-proof component but supported by a special design that will prevent leakage after the component is melt.

• The first method to achieve a fire-safe design by using a fire-proof component usually is referring as an inherently fire-safe valve. Usually this type of valve is a metal seated valve by using a graphite seat insert (in ball valve or butterfly valve) and graphite stem packing. By using graphite as a seat insert and stem packing, the graphite will remain stand even after fire exposure.

• The second method to achieve a fire-safe design by using a non fire-proof component usually is referring as fire-tested valve. This valve is using a thermoplastic seat material and a thermoplastic stem packing material such as PTFE. In the seat design, even though the seat is thermoplastic, it is designed so that when the thermoplastic is melting due to high temperature exposure the seal is still achievable by a body machined as a secondary seal. In the stem packing design, usually the thermoplastic seal is supported by a graphite seal as a secondary packing.

ESD Triggers

• Pressure sensing High & Low

These kind of triggers provide high and low pressure sensing on gas or liquids and can be fitted with either an automatic or manual reset.

• Fusible Link Fusible links are set to melt and activate an

ESD system in the event of fire.

PERFORMANCE MEASUREMENT FOR ESD VALVE

• For ESD valves, it is essential to know that the valve is capable of providing the required level of safety performance and that the valve will operate on demand.

• The required level of performance is dictated by the Safety integrity level (SIL).• The metric for measuring the performance of a safety function is called the

Average Probability of failure on demand (or PFDavg) and this correlates to the SIL level as follows:

SIL PFDavg

4 ≥ 10−5 to <10−4

3 ≥ 10−4 to <10−3

2 ≥ 10−3 to <10−2

1 ≥ 10−2 to <10−1

Types Of Performance Tests

There are 2 types of testing methods available:

• Proof test - A manual test that allows the operator to determine whether the valve is in the "as good as new" condition by testing for all possible failure modes and requires a plant shutdown. (GENERALLY DONE ONCE IN A YEAR OR TWO YEARS)

• Diagnostic Test - An automated on-line test that will detect a percentage of the possible failure modes of the shutdown valve. An example of this for a shutdown valve would be a partial stroke test. (GENERALLY DONE EVERY 6 MONTHS)

PARTIAL STROKE TESTING (PST)

• Partial stroke testing (PST) is a technique used in SIS to allow the user to test a percentage of the possible failure modes of a shut down valve without the need to physically close it.

• The PST is used to check the function of the safe position of ESD valves.

• A successfully executed partial stroke demonstrates that certain unresolved errors that would otherwise go undetected, such as spring fractures in the spring chamber of the pneumatic actuator.

• The test can be started both locally on the device in a time-controlled manner or from remote.

How is PST performed?• The positioner evacuates an output until the position

change defined in advance occurs. If this does not happen within the set time (timeout value), an alarm can be output.

• At the end of the test, the positioner moves the valve to the last valid position and reverts to the most recently active control mode.

• For documentation purposes, the test result is saved in the non-volatile memory.

Various PST Techniques Mechanical Jammers• A device is inserted into the valve and actuator assembly

that physically prevents the valve from moving past a certain point. These are used in cases where accidentally shutting the valve would have severe consequences, or any application where the end user prefers a mechanical device.

• Mechanical limiting methods are inexpensive in terms of capital and installation costs.

• These methods are manually initiated in the field and are manpower intensive.

• A limit switch or visual inspection is used to confirm valve movement.

• One of the biggest drawbacks to these methods is the lack of assurance that the valve is in or has been returned to normal status.

During normal operation the device is passive and will allow the valve to ESD on demand.

When a partial stroke test is required, the device is “engaged” and the ESD valve will only travel to the

specified percentage of stroke. Thedevice mechanically prevents movement past the interlock

Mechanical Partial Stroke Test Device shown in disengaged position

Mechanical Partial Stroke Test Device shown in engaged position.

PST Methodologies (Contd.) Position Control• Position control uses a positioner to move the valve to a pre-determined point. This

method can be used on rising stem and rotary valves.• Since most emergency block valves are not installed with a positioner, this method

does require installation of additional hardware.• Positioner operation also requires an analog output, which is typically not installed in

SIS applications. Consequently, cost is a major drawback for the position control method.

• A limit switch or position transmitter can be used to determine and document the successful completion of the tests.

• If a smart positioner is used for the position control, a HART maintenance station can collect the test information and generate test documentation. Of course, the use of a smart positioner and maintenance station further increases the capital cost.

• The positioner does contribute to the spurious trip rate during normal operation, since the positioner can fail and vent the air from the valve.

• But when a solenoid is installed between the positioner and the actuator, the safety functionality is never lost during the partial-stroke test. De-energizing the solenoid will shut the valve regardless of the positioner action.

PST Methodologies (Contd.) Solenoid• A partial-stroke test can be accomplished by pulsing a solenoid valve. The solenoid

can be the same solenoid used for valve actuation, resulting in a low capital and installation costs for the method.

• If the actuation solenoid valve is used, this method will also test the solenoid valve functionality.

• Valve travel confirmation is accomplished by a limit switch or position transmitter, allowing automatic documentation of test status.

• The test can be programmed in the SIS logic solver with the test being implemented automatically based on a programmed cycle time or initiated by the operator on a maintenance schedule.

• Since the valve is never bypassed or disabled, the valve remains available for shutdown during the test. As with the other partial-stroke testing methods, a maintenance bypass is required to allow maintenance to be performed on-line without a process shutdown.

• After all, the solenoid is being de-energized for the test and re-energized to stop the test.

• If the solenoid valve does not reset, the test becomes a trip.• The use of redundant solenoids can seriously reduce the probability of the spurious

trip.

Benefits Of PST• Reducing the probability of failure on demand.• Extension of the time between compulsory plant shutdowns.• Predicting potential valve failures facilitating the pre-ordering of

spare parts.• Prioritisation of maintenance tasks.• If the safety is of an appropriate level, the need for costly redundant

valves may be eliminated.

ASME B16.1 and B16.5. ASME B16.1 : Cast Iron Pipe Flanges and Flanged Fittings. This Standard for Classes 25, 125, 250 Cast Iron

Pipe Flanges and Flanged Fittings covers. ASME B16.5 : Pipe Flanges and Flanged Fittings. The standard includes flanges with rating class 150, 300, 400,

600, 900, 1500, and 2500 in sizes NPS 1/2 through NPS 24.ASME B16.10-199

Defines Face-to-Face Dimensions of valve bodies

ISA S75.19 For Hydro testing of Control Valves (Latest Edition)

ASME B16.34-1996 :Valves - Flanged, Threaded and Welded End Defines design criteria for valves with Flanged, Threaded and Welding ends Defines minimum wall thickness requirements Defines Pressure-Temperature Ratings for various materials Permits Assembled Hydrostatic Pressure Tests

ANSI B16.104-1976 (FCI 70-2): Standard for Control Valve Leakage Classification (Fluid Control Institute) Standard for Seat Leakage Classification Establishes test procedures and seat leakage classes Six Leakage Class Designations - Class I through VI

Standards Relevant to Control Valves

ANSI/ISA-75.05.01-2000 (R2005) Control Valve Terminology

ASME/ANSI B16.47 – 1996 Large Diameter Steel Flanges: NPS 26 through NPS 60

American Petroleum Institute (API): API STD 6F Fire Test for Valves API STD 598 Valve Inspection & Testing API STD 599 Metal Plug Valves – Flanged, Threaded and Welded Ends API STD 602 Steel, Gate, Globe & Check Valves for Sizes DN 100 and Smaller for the Petroleum and Natural Gas Industries API STD 608 Metal Ball Valves – Flanged, Threaded, and Welded Ends API STD 609 Butterfly Valves: Double Flanged Lug and Wafer Type. API STD 2000 Venting Atmospheric and Low Pressure Storage Tanks Non-refrigerated and Refrigerated

National Association of Corrosion Engineers (NACE): NACE MR0103 and NACE MR0175 and : Petroleum and Natural Gas Industries Materials for use in H2S-Containing

Environments in Oil and Gas Production Part 1: General Principles for Selection of Cracking-Resistant Irons – Part 3: Cracking-Resistant CRAs (Corrosion-Resistant Alloys) and other Alloys

VARIOUS STANDARDS @ On-Off valves• IEC61508: Functional safety of electrical/ electronic/ programmable electronic safety-

related systems• IEC61511: Functional safety of SIS for the process industry sector. It imposes additional

redundancy requirements to achieve high SIL rating; these can be mitigated where diagnostics are shown to be used to provide predictive maintenance.

• TUV Certificate: The purpose of this paper is to summarize the test and certification policies used during a TUV certification of a safety component/subsystem. These components/subsystems are typically electrical/electronic/ programmable electronic systems.

• API 598(Valve Inspection and Testing): The standard covers inspection, supplementary examination, and pressure test requirements for both resilient-seated and metal-to-metal seated gate, globe, plug, ball, check, and butterfly valves. Pertains to inspection by the purchaser and to any supplementary examinations the purchaser may require at the valve manufacturer's plant.

• ANSI/API 607(Fire Test for Soft-Seated Quarter Turn Valves): The standard covers the requirements for testing and evaluating the performance of straightway, soft-seated quarter-turn valves when the valves are exposed to certain fire conditions defined in this standard.

• ASME B16.10: Face to Face and End-to-End Dimensions of Valves

TESTS and CERTIFICATION @ Control valves1. For Sour Services and services with H2S, NACE MR-01-75 certification needed for valve material.

2. DIMENSIONAL TEST: The face-to-face dimensions of flanged globe-body control valves shall be as given in the relevant standard ASME B16.10.

3. HYDROSTATIC TEST: Control valves shall be hydrostatically tested in accordance with the standards specified for the particular type of valve.

4. SEAT LEAKAGE TEST: The seat leakage test shall be in accordance with ANSI/FCI 70.2 and IEC-60534-4,Standard for control valve leakage. The seat leakage test procedures shall be executed for all control valves of Class V or VI.

5. PERFORMANCE AND MECHANICAL OPERATION TEST: The control valve shall be completely assembled and fitted with all accessories.The performance and mechanical test shall include a Hysteresis test, a dead band test etc.The HYSTERESIS TEST shall consist of measuring the valve stem position for the following sequence of input signals: 50%, 75%, 100%, 75%, 50%, 25%, 0%, 25% and 50%. Hysteresis shall not exceed 0.5% of maximum valve stroke.The DEAD BAND TEST is expressed in percentage of the input span and shall be measured at 5%, 50% and 95% of the input span. The maximum dead band found shall not exceed 1% of rated input.

6. LOW TEMPERATURE TEST: A low temperature or a cryogenic test shall be made on selected control valves used in low temperature service (down to -50°C) or in cryogenic service (below -50°C).

7. CAPACITY TEST: If specified in the requisition, the actual Cv value shall be demonstrated by a test in accordance with IEC 60534-2-3.

8. IMPACT TESTING: Is done for carbon steel components used in low temperature services (below 15 degrees)

9. NON DESTRUCTIVE TESTS(NDT): Radiography Testing, Dye Test etc.

TESTS & CERTIFICATIONS @ On-off Valve

• NACE Certification for Corrosive/Sour Services and services with H2S, NACE MR-01-75 certification needed for valve material.

• DIMENSIONAL TEST: The face-to-face dimensions of flanged globe-body control valves shall be as given in the relevant standard ASME B16.10.

• HYDROSTATIC TEST: Control valves shall be hydrostatically tested in accordance with the standards specified for the particular type of valve.

• SEAT LEAKAGE TEST: The seat leakage test shall be in accordance with ANSI/FCI 70.2 and IEC-60534-4,Standard for control valve leakage. The seat leakage test procedures shall be executed for all control valves of Class V or VI.

• CRYOGENIC TEST: A low temperature or a cryogenic test shall be made on selected control valves used in low temperature service (down to -50°C) or in cryogenic service (below -50°C).

• IMPACT TESTING: Is done for carbon steel components used in low temperature services(below 15 degrees)

• NON DESTRUCTIVE TESTS(NDT): Radiography Testing, Dye Test

CONTROL VALVE SIZING CALCULATIONSControl valve Sizing is extremely critical and involves a lot of calculations. Being and EPC we don’t directly calculate a valve CV, but we must be aware of each ad every governing factor and be capable of choosing the most correct valve according to our requirements.

Flow Coefficient (CV)

The valve flow coefficient, CV is the number of U.S. gallons per minute of water at 60 degrees F which will pass through a given flow restriction with a pressure drop of 1 psi. For example, a control valve which has a flow coefficient, or CV, of 12 has an effective port area that it passes 12 gallons per minute of water with 1 psi pressure drop.Kv is the flow coefficient in metric units. It is defined as the flow rate in cubic meters per hour [m3/h] of water at a temperature of 16º celsius with a pressure drop across the valve of 1 bar.Now we have concept of Rated Cv and Calculated Cv.Rated Cv is maximum Cv of valve, ie. When the valve is fully open. This is provided by the vendor.Calculated Cv is flow coefficient calculated according to process conditions. It is always less then Rated Cv.

Symbol Description Unit

C Flow coefficient (Kv,Cv) Various (IEC 60534) see note 4

Cf Assumed flow coefficient for iteritive purposes

Various (IEC 60534) see note 4

d Nominal valve size mm

D Internal diameter of piping mm

D1 Internal diameter of piping mm

D2 Internal diameter of piping mm

Dc Orifice diameter mm

Fd Valve style modifier 1see note 4

FF Liquid critical pressure ratio factor 1

FL Liquid pressure recovery factor of a control valve w/o attached fittings

1see note 4

FLP Combined liquid recovery factor & piping geometry factor

1

FP Piping geometry factor 1

FR Reynolds number factor 1

Fץ Specific heat ratio factor 1

M Molecular mass of flowing fluid Kg/kmol

N Numerical constants Various see note 1

p1 Inlet absolute static presure measured at point A

kPa or bar See note 2

Symbol Description Unit

p2 outlet absolute static presure measured at point B

kPa or bar See note 2

Pc Absolute thermodynamic critical pressure

kPa or bar

Pr Reduced pressure (p1/pc) 1

pv Absolute vapour pressure of the liquid at inlet temperature

kPa or bar

dp Differential pressure between upstream and downstream pressure taps (P1-P2)

kPa or bar

Q Volumetric flow rate M3/h

Rev Valve Reynolds number 1

T1 Inlet absolute temperature K

Tc Absolute thermodymanic critical temperature

K

ts Absolute reference temperature for standard cu.metre

K

Tf Reduced temperature (T1/Tc) 1

W Mass flow rate Kg/h

x Ratio of pressure differential to inlet absolute pressure(dp/p1

1

xT Pressure differential ratio factor of a control valve w/o attached fittings at choked flow

1See note 4

xTP Pressure differential ratio factor of a control valve w/o attachedfittings at choked flow

1See note 4

SIZING TERMINOLOGY

Symbol Description UnitY Expnsion factor 1

Z Compressibility factor 1

v Kinematics viscosity M2/secSee note 3

ρ1 Density of fluid at p1 and T1 Kg/m3

ρ1/ ρ0 Relative density (ρ1/ ρ0) =1 for water at 15ºC

1

ץ Specific heat ratio 1

ζ Velocity head loss coefficient of a reducer, expander or other fitting attached to a a control valve

1

ζ1 Upstream velocity head loss coefficient of fitting

1

ζ2 downstream velocity head loss coefficient of fitting

1

ζB1 Inlet Bernoulli coefficient 1

ζB2 outlet Bernoulli coefficient 1

NOTE1. To determine the units for the numerical constants,

dimensional analysis may be performed on the appropriate equations using the units given in table

2. 1 bar = 102 kPa = 105 Pa3. 1 centistokes = 10-5 m2/sec4. These values are travel related and should be stated by

the manufacturer5. Volumetric flow rates in cubic metres per hour, identified

by the symbol Q, refer to standard conditions. The standard cubic metre is taken at 1013.25 mbar and either 273 K or 288K

DEFINATIONS TO REMEMBER

Sizing equations for Non-Compressible Fluids

To Note

DP choked flow or ΔPch = FL2 (p1-FF x pv)

Here ΔP < ΔPch

Where. C= Cv in USG/min.Q flow rate in M3/hρ1- density at pressure p1 and temp. T1

ρ0 -density 1.0 at 15ºC

N1 -Numerical constant

dp – p1-p2

FL Liquid pressure recovery Factor

FF Liquid critical pressure ratio factorPv – absolute vapour pressure at inlet kPa / barp1 inlet absolute pressure in kPa or barp2 outlet absolute pressure in kPa or bar Specific weight at inlet conditions ρg

Where. C= Cv in USG/min.Q flow rate in M3/hρ1- flowing density at pressure p1 and temp. T1ρ0 -density 1.0 at 15ºCN1,N6 -Numerical constantdp – p1-p2 FL Liquid pressure recovery FactorFF Liquid critical pressure ratio factorpv – absolute vapour pressure at inlet kPa / barp1 inlet absolute pressure in kPa or barp2 outlet absolute pressure in kPa or barFLP combined pressure recovery factor and piping geometry factorFP – piping geometry factor specific weight at inlet conditions

(2a)

Choked flowThe basic liquid sizing equation tells us that the liquid flow rate through a control valve is proportional to the square root of pressure drop. This simple relationship is shown graphically by the green portion of the graph in Figure 1. (Note that the scale of the horizontal axis is the square root of pressure drop.) This linear relationship does not always hold true. As the pressure drop is increased, the flow reaches a point where it no longer increases. Once this happens, additional increases in pressure drop across the valve do not result in additional flow, and flow is said to be choked. Here we will call this limiting or choking pressure drop the Terminal Pressure Drop, ΔpT. (The same thing is also sometimes referred to as the Allowable Pressure Drop, Δpallowable, sometimes as the Maximum Pressure drop, ΔpMax, and sometimes as the Critical Pressure Drop, ΔpCrit.)

To Note

DP choked flow or ΔPch = FL2 (p1-FF x pv)

Here ΔP > = ΔPch

When above is true, the flow is choked.

Hence, for Non-Compressible fluids(liquids etc) ΔPmin is taken in the denominator ie. Smaller value between ΔP and Δ Pch

Where. C= Cv in USG/min.Q flow rate in M3/hρ1- density at pressure p1 and temp. T1ρ0 -density 1.0 at 15ºCN1 -Numerical constantdp = p1-p2 FF Liquid critical pressure ratio factorpv – absolute vapour pressure at inlet

kPa / barp1 inlet absolute pressure in kPa or barp2 outlet absolute pressure in kPa or barFP – piping geometry factorFL Liquid pressure recovery FactorFF Liquid critical pressure ratio factor

Where. C i Cv in USG/min.Q flow rate in m3/hρ1 density in kg/m3 at pressure p1 and temp. T1Ρ1/ρ0 =1 for water at 15ºCN1 -Numerical constantdp p1-p2 FF Liquid critical pressure ratio factorpv absolute vapour pressure at inlet kPa / barp1 inlet absolute pressure in kPa or barp2 outlet absolute pressure in kPa or barFP piping geometry factorFL Liquid pressure recovery FactorFLP combined pressure recovery factor and piping geometry factor

Where. C= Cv in USG/min.Q flow rate in m3/hρ1- density in kg/m3 at pressure p1 and temp. T1Ρ1/ρ0 =1 for water at 15ºCN1 -Numerical constantdp (p1-p2 ) p1 inlet absolute pressure in kPa or barp2 outlet absolute pressure in kPa or barFR Reynold’s number factor

Sizing equations for Compressible Fluids

Where. C= Cv in USG/min.Q flow rate in m3/hW mass flow rate in kg/hγ expansion factorN6,N8,N9 -Numerical constantM molecular mass of fluid kg/kmol p1 inlet absolute pressure in kPa or barp2 outlet absolute pressure in kPa or barT1 Inlet absolute temperature in KelvinZ compressibility factorx (p1-p2)/p1

Where. C= Cv in USG/min.Q flow rate in m3/hW mass flow rate in kg/hγ expansion factorN6,N8,N9 -Numerical constant

M molecular mass of fluid kg/kmol p1 inlet absolute pressure in kPa or barp2 outlet absolute pressure in kPa or barT1 Inlet absolute temperature in KelvinZ compressibility factorx (p1-p2)/p1

FP – piping geometry factor

Where. C= Cv in USG/min.Q flow rate in m3/hW mass flow rate in kg/hγ expansion factorN6,N8,N9 -Numerical constantM molecular mass of fluid kg/kmol p1 inlet absolute pressure in kPa or barp2 outlet absolute pressure in kPa or barT1 Inlet absolute temperature in KelvinZ compressibility factorx (p1-p2)/p1x T pressure differential pressure factor – vendor data

To Note

X>=FyXt

When above is true, the flow is choked.

At choked flow, the gas attains sonic velocity, 1Mach

Where. C Cv in USG/min.Q flow rate in m3/hW mass flow rate in kg/hγ expansion factorN6,N8,N9 -Numerical constantM molecular mass of fluid kg/kmol p1 inlet absolute pressure in kPa or barp2 outlet absolute pressure in kPa or bar

T1 Inlet absolute temperature in KelvinZ compressibility factorFP piping geometry factorxTP pressure differential pressure factor – vendor dataFγ specific heat ratio factorρ1- density in kg/m3 at pressure p1 and temp. T1