PRESENTATION ON VALVES

1
PRESENTATION ON VALVES
2

• OBJECTIVES
• Explain the various ways in which valves control
  fluid flow in piping systems.
• Identify gate, globe, needle, ball, butterfly,
  plug, and check valves,
• Selection Criteria
• Fertilizer Plant Experience

3

• A valve is a device that regulates the flow of
  substances (either gases, fluidized solids,
  slurries, or liquids) by opening, closing, or
  partially obstructing various passageways.
• Body
• The majority of the valve consists of the valve
  body, including most of the exterior. The valve
  body is the vessel or casing that holds the fluid
  going through inside the valve. Valve bodies are
  most commonly made of various metals or plastics.
• Ports
• The body has two or more openings, often called
  the ports, through which the fluid can enter or
  leave the valve.
• Discs and rotors
• Inside the valve body, flow through the valve may
  be partly or fully blocked by an object called a
  disc. Although valve discs of some kinds of
  valves are traditionally disc-shaped, discs can
  come in various shapes. Although the valve body
  remains stationary within the fluid system, the
  disc in the valve is movable so it can control
  flow.

4

• Seat
• The valve seat is the interior surface in the
  body which contacts or could contact the disc to
  form a seal which should be leak-tight,
  particularly when the valve is shut. If the disc
  moves linearly as the valve is controlled, the
  disc comes into contact with the seat when the
  valve is shut.
• Stem
• The stem is a rod or similar piece spanning the
  inside and the outside of the valve, transmitting
  motion to control the internal disc or rotor from
  outside the valve. Inside the valve, the rod is
  joined to or contacts the disc/rotor. Outside the
  valve the stem is attached to a handle or another
  controlling device.
• Bonnet
• A bonnet basically acts as a cover on the valve
  body. It is commonly semi-permanently screwed
  into the valve body.
• Spring
• Many valves have a spring for spring-loading, to
  normally shift the disc into some position by
  default but allow control to reposition the disc.
  Relief valves commonly use a spring to keep the
  valve shut, but allow excessive pressure to force
  the valve open against the spring-loading,

5
Flow thru a valve
6
Type of Valves
7

• Ball valve, which is good for on/off control.
• Butterfly valve, particularly in large pipes.
• Check valve or Non-return valve, allows the fluid
  to pass in one direction only. Check valves are
  designed to restrict the flow to one direction. 
  If the flow reverses direction, the check valve
  closes.
• Diaphragm valve, a sanitary valve predominantly
  used in the pharmaceutical industry
• A flow control valve maintains a constant flow
  rate through the valve.
• Gate valve, mainly for on/off control.
• Globe valve, which is good for regulating flow.
• Hydraulic valve (diaphragm valve).
• Needle valve for gently releasing high pressures.
  
• Pilot valves regulate flow or pressure to other
  valves.
• Plug valve, for on/off control.
• A pressure reducing valve (PRV), also called
  pressure regulator, reduces pressure to a preset
  level downstream of the valve.
• Relief valves are used to regulate the operating
  pressure of incompressible flow. 
• Safety valves are used to release excess
  pressure in gases or compressible fluids.

8

• Equal Percentage  equal increments of valve
  travel produce an equal percentage in flow change
• Equal Percentage (most commonly used valve
  control)a.  Used in processes where large
  changes in pressure drop are expectedb.  Used in
  processes where a small percentage of the total
  pressure drop is permitted by the valvec.  Used
  in temperature and pressure control loops

9

• Linear  valve travel is directly proportional to
  the valve stoke
• Lineara.  Used in liquid level or flow loopsb. 
  Used in systems where the pressure drop across
  the valve is expected to remain fairly constant
  (ie. steady state systems)

10

•   Quick opening  large increase in flow with a
  small change in valve stroke
•   Quick Openinga.  Used for frequent on-off
  serviceb.  Used for processes where "instantly"
  large flow is needed (ie. safety systems or
  cooling water systems)

11
TYPE OF VALVES
12
Gate Valves Best Suited Control  Quick
Opening Recommended Uses1.  Fully open/closed,
non-throttling2.  Infrequent operationApplicat
ions  Oil, gas, air, slurries, heavy liquids,
steam, noncondensing gases, and corrosive
liquids Advantages                            
Disadvantages1.  High capacity
                      1.   Poor control2.  Tight
shutoff                         2.   Cavitate at
low pressure drops3.  Low cost
                              3.   Cannot be used
for throttling4.  Little resistance to
flow  
13

• Best Suited Control 
• Linear and Equal percentage
• Recommended Uses1.  Throttling service/flow
  regulation2.  Frequent operation
• Applications  Liquids, vapors, gases,
• corrosive substances, slurries
• Advantages                        
  Disadvantages1.  Efficient throttling
                1.   High pressure drop2. 
  Accurate flow control        2.  More expensive
  than other valves3.  Available in multiple
  ports

14

• Best Suited Control
• Quick opening, linearRecommended Uses
• 1.  Fully open/closed, limited-throttling2. 
  Higher temperature fluids
• Applications Most liquids, high temperatures,
  slurries
• Advantages                        
  Disadvantages1.  Low cost                       
      1.   Poor throttling
  characteristics2.  High capacity
                     2.   Prone to
  cavitation3.  Low leakage and maint.4.  Tight
  sealing with low torque 

15

• Best Suited Control
• Linear, Equal percentage
• Recommended Uses  1.  Fully open/closed or
  throttling services2.  Frequent operation
• Applications  Liquids, gases, slurries, liquids
  with suspended solids
• Advantages                       
  Disadvantages1.  Low cost and maint.        1. 
  High torque required for control2.  High
  capacity                 
• 2.   Prone to cavitation at lower
  flows3.  Good flow control

16
TYPE OF CHECK VALVES
17
VALVES- SELECTION CRITERIA

• Control valves
• Sizing
• Control valves shall be sized in compliance with
  standard ISA S75.01 using calculation methods
  given in the Masoneilan Handbook for Control
  Valve sizing ".
• In general the Cv selected shall equal at least
  the maximum Cv calculated multiplied by 1.3.
• Butterfly valves shall be sized for a maximum
  opening angle of 60 with the exception of those
  provided with a characterised disc, which shall
  be sized for a maximum opening angle of 90.
• Normally the valves exclusively envisaged for
  shut-off service shall be line size.
  Alternatively, they could be sized as control
  valves.
• The fluid velocity at the valve outlet flange
  shall not exceed 6 m/sec for liquids whereas the
  velocity of gas or vapour shall not normally
  exceed 0.3 Mach under operating conditions.
• In order to reduce the fluid velocity below such
  limits use can be made of widely-sized valves
  equipped with reduced trims.
• Fluid velocity values could exceed the
  above-mentioned limits in the case of valves
  provided with a labyrinth plug, cage trim or
  angle body.

18

• Choice of type
• Without establishing rigid rules it is generally
  possible to assume that the following types of
  valves are used
• Globe valves for most common applications
• Butterfly valves if low pressure drops and high
  flow capacities are required
• "Characterised-ball valves (e.g. V-ball" type)
  for fluids which entrain solids or which easily
  crystallise
• Angle valves when high pressure drops on gas or
  erosive fluids
• Three-way valves if the flow must be split into
  two fluid streams
• Saunders valves for corrosive or dirty and muddy
  fluids.

19

• Choice of body
• Valves with bodies having nominal dimensions of 1
  1/4", 2 1/2" and 5 shall not be used.
• In the case of lines with a diameter of up to 1"
  the valve size shall normally equal that of the
  line.
• In the case of lines with a diameter larger than
  1 the valve size shall not be less than 1. -
• The body material shall be chosen in compliance
  with materials required in the line specification
  and, in any case, shall be suitable for the
  process fluid.
• Valves shall generally have flanged connections
  as per rating envisaged in the line specification
  with the exception of valves with a nominal
  diameter smaller than or equal to 1 1/2 which
  shall have a minimum rating of 300 ANSI.
• Some types of valves such as characterised ball
  valves, butterfly valves or valves with an
  eccentric rotating plug shall be of the wafer
  type, i.e. suitable to be installed between
  pipeline flanges.
• Self-actuating valves could have a nominal
  diameter smaller than 1 irrespective of the pipe
  diameter.

20

• Trim selection
• Control characteristic
• In the case of globe valves or of valves equipped
  with an eccentric rotating plug the trim
  characteristic shall generally be chosen on the
  basis of the following criteria
• quick opening for valves exclusively envisaged
  for shut-off service
• equal percentage if the valve pressure drop at
  the maximum flow rate is less than about one
  third of the overall system pressure drop (valve
  line)
• linear in all other cases.
• In the case of butterfly valves, of valves with
  characterised ball (e.g. V-ball) and of angle
  valves the characteristic will depend on the type
  of valve as well as on the supplier selected.

21

• Trim for use under severe conditions
• In the presence of liquids which, because of
  particular operating conditions, can give rise to
  cavitation phenomena, use shall be made of
  special trims (e.g. multi-drops cage trim) so as
  to avoid that similar phenomena may take place
  or, at least, to reduce their effect.
• The maximum acceptable noise level permanently
  produced by control valves (measured at one metre
  downstream from the valve and one metre from the
  pipe) shall not exceed 85 dB (A).
• In order to ensure that this limit is not
  exceeded when high pressure drops and large gas
  flow-rates are involve. use shall be made of
  special trims (e.g. labyrinth plugs) or to
  suitably designed valves (e.g. multi-step angle
  valves).
• Levels in excess of 85 dB (A) can be accepted in
  the case of noise of limited duration in
  accordance with provisions envisaged in OSHA
  regulations.

22

• Construction and materials
• With the exception of Saunders valves, the trim
  of valves shall be of AISI 316 unless the fluid
  and operating conditions require a more suitable
  material.
• The plug, seat and stem guide posts shall be
  fully stellite coated in the following cases
• when the process fluid is a liquid with suspended
  solids
• in the presence of liquids which consistently
  vaporise in the valve body
• if the pressure drop across the valve (at the
  maximum flow rate) exceeds or is equal to 10 bar
• if the operating temperature exceeds 280 C.
• The use of special materials recommended by the
  control valve manufacturer could be considered
  Instead of stellite -coating.

23

• Bonnet
• Bonnet shall generally be of standard execution.
  However, it shall be supplied as follows
• extended if the fluid operating temperature is
  comprised between -40 and 0 C
• finned if the operating temperature is above 230
  C
• extra-long if the operating temperature is below
  -40 C

24

• Packing
• The packing shall be of
• Teflon if the fluid operating temperature is
  below 230 C
• Graphite-asbestos if the operating temperature is
  above 230 C.
• The use of special packing materials may be
  considered according to the control valve
  manufacturer recommendation.
• Double packing will be used on toxic services (
  wet H2S, etc.).

25

• Trim tightness
• The control valve seat leakage class shall be
  established on the basis of ANSI B 16.104.
• If the allowed seat leakage does not exceed class
  II double seat valves can be used.
• Valve tightness corresponding to class III, IV or
  V will be achieved via a metal to metal
  single-seat trim.
• If the seat leakage required is of class VI
  provision shall be made for a soft insert in the
  seat as long as the operating temperature is less
  than about 200 C and the pressure drop, with the
  valve closed, does not exceed 15 bar.
• ESD valves shall be Class V metal to metal as
  minimum.
• Special requirements could be met on the basis of
  past experience of qualified suppliers.

26

• Stream flow action
• In the case of valves for shut-off service only
  the process fluid action shall coincide with that
  of the valve when control air pressure fails.
• In case of valves used for fluid throttling the
  following criteria shall generally apply
• angle valves fluid action tending to close
• valves with eccentric rotating plug the fluid
  action shall coincide with that of the valve in
  the case of control air outages
• other types of valves (globe, ball, etc.) fluid
  action tending to open.
• However, special considerations could impose a
  different fluid action

27

• Hand-wheel and bypass assembly
• Control valves shall be either supplied with a
  manual hand-wheel or envisaged with a bypass
  assembly. Shut-off valves shall be provided
  without bypass hand-wheel shall be provided only
  if demanded by operation needs.
• Control valves sized 3" or less shall be provided
  with both isolating and bypass valves. Valves
  with body dimensions exceeding 3 shall normally
  be supplied with the hand-wheel.
• Control valves exceeding 3 and installed on
  essential services (e.g. main lines for fuel,
  cooling water, etc.) or on corrosive, erosive or
  other special fluids shall be supplied with both
  isolating and bypass valves if so envisaged in
  the process diagrams.

28

• Valves for emergency shutdown service (ESD)
• Valves controlled by the emergency shutdown
  system (ESD) and used either for isolating or for
  depressurising the plant under emergency
  conditions shall be supplied in accordance with
  process requirements. These valves shall be
  fitted with actuators designed in such a way
  that, in the event of control air failure, they
  can drive the plant toward safe conditions even
  when the envisaged maximum pressure drop, caused
  by the process fluids, is applied to the valve
  ports.
• If there is no return spring (double acting
  actuators) provision shall be made for air
  accumulators with a storage capacity suitable for
  the execution of 2 strokes.
• Each ESD valve shall be equipped with one
  proximity type limit switch for remote indication
  of the trip position.
• ESD valves shall be provided with automatic
  pilots or solenoid valves for their remote
  control and with local facilities for manual
  reset.
• Solenoid valves in hazardous area will be
  explosion proof.

29
(No Transcript)
30
(No Transcript)
31
(No Transcript)
32
(No Transcript)
33
(No Transcript)
34
(No Transcript)
35
(No Transcript)
36
(No Transcript)
37
(No Transcript)
38
(No Transcript)
39
THANK YOU
40
CavitationIf the speed through the valve is high
enough, the pressure in the liquid may drop to a
level where the fluid may start bubble or flash.
The pressure recovers sufficiently and the
bubbles collapse upon themselves. Cavitation may
be noisy but is usually of low intensity and low
frequency. This situation is extremely
destructive and may wear out the trim and body
parts of the valve in short time.
41
Cavitation can be avoided by using more than one
control valve or more convenient - a multistage
control valve. "vena contracta" is much lower for
a single stage valve than a multi stage valve.
Depending on the pressure drop and the
temperature of the fluid its possible to avoid
cavitation conditions using more than one stage
in a valve
42
(No Transcript)
43
(No Transcript)
44
(No Transcript)
45
(No Transcript)
46
(No Transcript)
47

• Safety-Relief valve sizing
• With the exception of safety valves for liquid
  thermal expansion, safety valves shall be sized
  in compliance with formulae and calculation
  methods given in API RP 520 and in accordance
  with local codes keeping into account all
  possible reasons of intervention.
• Whenever possible and particularly when very high
  flow rates requiring the use of several spring
  loaded safety valves are involved or when the
  operating pressure is very close to the protected
  vessel design pressure, use shall be made of
  pilot-operated safety valves.
• Dimensions of safety valves for liquid thermal
  expansion shall generally be 3/4 x 1" NPT.

48

• Set pressure, overpressure, spring set pressure
• The set pressure, which is defined as the valve
  opening pressure measured at the valve inlet,
  shall not exceed the design pressure of the
  protected equipment except in cases where the
  flow rate calculated is discharged by more than
  one safety device (safety valve or bursting
  disc). In the latter case, at least one safety
  device shall open at a pressure not exceeding the
  lowest design pressure among all the protected
  vessels the other device/s could open at a
  higher pressure without exceeding 105 of the
  previously mentioned lowest design pressure.
• The overpressure, which is defined as the
  increase in pressure above the set pressure
  required for the valve to discharge the full flow
  rate - expressed as a percentage of the set
  pressure - shall not be
• lower than 15 for valves which discharge liquids
• higher than 10 for valves which discharge gas
  and vapour for any cause of intervention except
  for fire, in which case a set pressure not
  exceeding 21 shall be permitted.
• The sum of the set pressure and overpressure
  shall not exceed 110 of the lowest design
  pressure of the protected equipment.
• The spring set pressure (setting carried out on a
  test bench and under atmospheric back pressure)
  shall equal the set pressure if the valve
  discharges directly into the atmosphere or is
  fitted with balancing bellows in all other cases
  it shall equal the set pressure less the maximum
  back pressure (with the valve closed) except for
  pilot operated valves.

49

• Construction, materials, accessories
• The body material shall be chosen in compliance
  with what envisaged in the line specifications
  and shall be suitable for the process fluid.
• Internals shall be of stainless steel unless the
  fluid and process conditions require a more
  suitable material.
• Whenever possible, the same material shall be
  used for the balancing bellows.
• The spring material shall be chosen according to
  the product discharge temperature.
• The following shall generally be used
• AISI 304 or AISI 316 for discharge temperatures
  between -240 C and -60 C
• phosphatised carbon steel for discharge
  temperatures between -60 C and 230 C

50

• phosphatised tungsten steel for discharge
  temperatures between 230 C and 538 C
• for temperatures outside the above ranges the
  material shall be agreed upon with the
  manufacturer.
• Connections shall generally be flanged the
  rating of the inlet connection shall be chosen
  according to the trip conditions and that of the
  outlet connection shall normally be rated ANSI
  150.
• Valves sized 3/4" x 1" shall generally be
  provided with threaded connections ANSI B 1.20.1
  NPT.
• Provision shall normally be made for balancing
  and sealing bellows in the following cases
• when the process fluid contains lethal or toxic
  substances
• when the variable back pressure exceeds the
  safety valve set pressure by 10
• when the imposed back pressure (i.e. with the
  valve closed) is higher than the atmospheric
  pressure and the difference between the set
  pressure and normal operating pressure would,
  without the bellows, be less than 10 of the set
  pressure.
• Alternatively, pilot operated valves can be used.
• A lifting lever shall be provided when the
  process fluid is steam or air where required by
  the governing code.

51
Actuator, positioner and accessories

• Actuator
• All control valves without positioner shall
  generally be provided with a pneumatic actuator
  with a spring range of 0.2 1 bar.
• Other spring ranges, in particular for shut-off
  valves, could be used either to meet operating
  requirements or to limit actual valve overall
  dimensions.

52

• Positioner
• With the exception of the shut-off valves, to be
  provided without positioner, control valves shall
  be supplied with a pneumatic positioner in the
  following cases
• when the valve is employed in split-range service
• when the valve nominal diameter is larger than 1
• when the bonnet is not standard
• when the actuator signal differs from 0.2-1 bar
• under laminar motion conditions (very viscous
  fluids, etc)
• of consistent amounts of flashing liquids
• when the valve pressure drop., at the maximum
  operating flowrate, exceeds 5 bar for single
  seated valves or 10 bar for double seated valves.
• The positioner shall be supplied with a bypass
  and a set of pressure gauges. No bypass will be
  provided for valves in split-range service or
  when the input and output signal to from the
  positioner are different.