All Fluid Control Valves Types- Instrumentation

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All Fluid Control Valves Types

Cage guided globe valve

Cage guided globe valve

Globe valve

Advantages

  • rugged construction
  • linear relationship between the control signal and valve stem movements
  • wide range of trims and accessories allowing the flow characteristics to be tailored to the application
  • anti-cavitation trim for liquid applications
  • noise attenuation trim for gaseous applications
  •  wide range of designs for corrosive, abrasive, high temperature and high pressure applications
  • relative small values for dead band and hysteresis.

Disadvantages

  • at larger sizes, globe valve is expensive compared with other styles.
  • relatively high mass and a lower capacity than, for example, ball of butterfly valves.

Extension bonnet

Extended bonnet in which the stuffing box is located further away from the process medium allows the process medium temperature to be extended up to 800 °C or more.

Packing box trim

Includes various combinations of all, or part of, the following:
  1. Packing
  2. Packing nut
  3. Packing follower
  4. Lantern ring
  5. Packing spring
  6. Packing flange
  7. Packing flange studs or bolts
  8. Packing flange nuts
  9. Packing ring
  10. Packing wiper ring
  11. Felt wiper ring
Packing box trim
Packing box trim
Packing box trim

 

PTFE V-ring packing

Construction

  • Moulded in PTFE V or chevron rings
  • Spring loaded and self adjusting

Application

  • Resistant to most known chemicals
  • Handles strong acids and alkali solutions
  • Not suitable for molten alkali metals.
  • Suitable for temperatures from –40 up to 230°C
  • Requires extremely smooth stem finish to seal properly (1 μm)
  • Lubrication not required
  • Not suitable for nuclear service (PTFE destroyed by radiation)
Typical standard V-ring packing arrangement

Graphite filament packing

Construction

  • Light weight graphite/carbon fibres, twisted together and interlock braided.
  • Contains a special lubricant to provide a bearing film and prevent wicking.

Application

  • Severe service packing.
  • Handles strong acids and alkali solution except fuming nitric acid, oleum and fluorine.
  • Handles high temperatures (up to 650°C) and extremely high shaft speeds.
  • Produces high stem friction
  • Lubrication not required
Typical double graphite packing arrangement
double graphite packing
Electrochemical series
Electrochemical series
Valve plug contours
Plug hard facing variations
Seat retention
Seat retention

Globe valve

Single seat top guided control valve showing details of the plug and seat
Globe valve
Balanced port

 

Angle valve
angle valve

Bar stock

Can be machined from any metallic bar stock material, or even plastic Often specified for corrosive applications.When exotic metal alloys are required, a bar stock body is normally less expensive than a body produced from a casting.

Gate valve

  • The gate valve is an excellent valve for service that requires either full or no flow.
  • When fully open, the gate valve has no flow restriction — with the flow area equal to the full cross-sectional area of the line.
  • Since flow is straight through the line, pressure drop across a gate valve is only about 1/50th of that of a globe valve of comparable size.
Gate valve

Advantages

  • can be left open or closed on a variety of water, gas and chemical duties for long periods of time with the sure knowledge of satisfactory operation when required.

Disadvantages

  • close regulation of flow is not possible because throttling only occurs when the valve is in an almost shut position, where most of the flow reduction occurs.
  • repeated movement of the disc near the point of closure against upstream pressure can create a drag between the seat on the downstream side and may gall or score the seat faces.
  • the high-velocity flowing liquid impinging against a partially open disc or wedge produces vibration that can damage seating surfaces and score the downstream side.

 

 

 

Pinch valve

Advantages

  • Simple and cost effective
  • excellent resistance to abrasion – ideal for use on slurries.
  • turbulence is minimal — thus also increasing the life of the valve.
  • may be used very effectively as control valves in a number of applications where abrasion, sewerage, and corrosion is a factor.

Disadvantages

  • very high forces are required to operate the pinch valve and keep them closed.
  • at 600 kPa a force of over 8000 kg is required to close and seal a 300 mm valve.
  • restricted to low pressures (below 400 kPa) and low velocities.

Diaphragm valve

  • linear flow characteristics make it well suited to throttling or modulating duties at modest differential pressures.
  • wide range of applications (175°C max. and 16 bar max.).
  • all working parts are isolated from the line media

Ball valve

Characterised V-notch ball valve

  • In the characterised ball segment valve the opening between the ball and seal are modified to provide different flow characteristics.
  • The V-notched ball segment produces an equal percentage flow characteristic  and provides a shear-on-close action — making it suitable for slurry applications and for fluids that include fibrous and stringy material.
V-notch ball valve
Other contours include the U-notch and parabolic-notch providing differing flow characteristics

Ball segment valve

  • In the ball segment valve the shaft is centrally mounted to give constant contact between the segment and the seat during opening and closing.
  • Suitable for both clean liquids and fibre suspensions, the seat acts like a scraper keeping the surface of the segment clean

Eccentric shaft segmented ball valve

  • In this version the shaft is located eccentrically.
  • This enables the pressure between the segment and the seat to be increased by increasing the torque on the shaft.
  • Typical applications are clean, hot media such as steam and gases, where it is necessary to use a stellite seat.
  • Due to the eccentricity, friction between the seat and segment is avoided — resulting in increased valve life.

Butterfly valve

  • From 100 mm upwards, the ball valve tends to become bulky …
  •  …and if manufactured of a sophisticated heat and/or corrosion resistant material can become expensive.
  • This has led to the development of the butterfly valve
Butterfly valve
  • Rotation of the conventional butterfly valve is limited to about 60°
  • This is because, as the disc is rotated nearer to the fully open position the leading and trailing edges of the disc are shadowed by the shaft.
  • The body of the valve is lined with an elastomeric material that is held in position in the body by either bonding or mechanical means.
  • As the disc moves into the closed position, the material of the liner is an interference fit with the disc edge.
  • This determines the pressure sealing capability and the torque required to close and open the valve into or from the full closed position.

Eccentric disk butterfly valve

  • In the offset disc, or high performance butterfly valve, the disc is offset in two planes, resulting in an eccentric rotating or camming action.
  • This results in the disc moving away from the seat after approximately I0° of rotation, and equal loading of the seat whenever the valve is closed.
Eccentric disk butterfly valve
  • Seat designs vary from pressure energised reinforced PTFE, to the solid filled PTFE.
  • Advantages include:
  • better seal performance,
  • lower dynamic torque
  •  higher allowable pressure drops.
  • The improvement in seal performance is because the disc cams in and out of the seat and thus contact is made only at closure.
Butterfly valve characteristics

Plug valve

  • One of the oldest valves in use
  • When the plug is rotated it permits flow through the port of the plug — whilst a 90° turn in either direction completely blocks the flow path.

 

Camflex eccentric plug valve 1

  • The centre of the spherical seating surface is offset from the shaft axis.
  • The one piece shaft, which is connected to an actuating arm linked to the actuator piston rod, rotates the plug face in an eccentric, cam-like motion, down and forward into the seat.
  • As the plug rotates into its seated position, it makes no contact with the seat until the actual moment of seating.

Camflex eccentric plug valve 2

  • Once seating occurs, a positive seal between plug and seat is achieved by the elastic deformation of the plug arms
  • When the plug seats, the arms ‘flex’ such that additional actuator thrust forces the plug deeper and into tighter contact with the seat.
  • The shaft connection allows the plug to center itself along the shaft axis.
The angle of contact between the plug and seat lets the plug wipe larger particles off the seating surfaces yet permits no rubbing, once contact is established

 

Camflex eccentric plug valve 3

  • Standard leakage classifications  of metal to metal seating surfaces conform to ANSI B16.104 Class IV.
  • For ANSI B16.104 Class VI (bubble tight) use is made of PTFE ` soft seat construction.
  • Another feature of the Camflex valve is that only one-third the amount of force required to stroke a conventional single-seated globe valve is required of the Camflex actuator to stroke against a given pressure drop.
  • The spherically shaped, eccentric rotating plug provides an inherent flow characteristic that is essentially linear.
  • As the plug approaches the seat, the characteristic curve is modified as the rate of change in flow is reduced smoothly until the plug actually contacts the seat.

Camflex eccentric plug valve 4

  • Integral extension bonnets make this valve acceptable on cryogenic fluids and temperatures to 400°C.
  • It also eliminates a gasket joint at the body to bonnet interface and associated potential for leakage.
  • Although not specifically designed for it, this design has proven successful on hard-to-handle moderate slurry service, ranging from alumna oxide to low-pressure oil and catalyst.
Please read also: Basic Control Valve Principles
Please read also:  CALIBRATION OF VALVES WITH ACTUATOR & ACCESSORIES
         The End ! Enjoy ! Comment to Blog

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7 Responses

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