Monday, September 28, 2015

Gate Valve

A Gate Valve is also know as Sluice Valve, is a valve that opens by lifting a round or rectangular gate/ wedge out of the path of the fluid.



Gate valves are primarily designed to start or stop flow, and when a straight-line flow of fluid and minimum flow restriction are needed. In service, these valves generally are either fully open or fully closed.

Construction of a Gate Valve

Gate valves consists of three main parts: body, bonnet, and trim. The body is generally connected to other equipment by means of flanged, screwed or welded connections. The bonnet, which containing the moving parts, is attached to the body, usually with bolts, to permit maintenance. The valve trim consists of the stem, the gate, the disc or wedge and the seat rings.


Discs of Gate Valve


Gate valves are available with different disks or wedges.

The most common types of Discs are :

Solid Wedges
Solid wedge is the most commonly used disk by its simplicity and strength.
A valve with this type of wedge can be installed in each position and it is suitable for almost all liquids. The solid wedge is a single-piece solid construction, and is practically for turbulent flow.


Flexible Wedges

Flexible wedges are featured with mechanical flexibility to adjust it's own shape following the shape of body seats for a tightly secured mutual contact. This is particularly important when larger Gate Valves service at extremely high pressure and temperature, where temporary deformation of the seats always occur. With Flexible Wedges operational torque is smaller, seat wear is less and valve closure is tighter.




Flexible Wedge Front View

Stem to Wedge Connection
Flexible Wedge Side View
Flexible wedge is a one-piece disc with a cut around the perimeter to improve the ability to correct mistakes or changes in the angle between the seats.
    The reduction will vary in size, shape and depth. A shallow, narrow cut gives little flexibility but retains strength.

      A deeper and wider cut, or cast-in recess, leaves little material in the middle, which allows more flexibility, but compromises strength.


      Split Wedges
      Split wedge is self-adjusting and self-aligning to both seats sides. This wedge type consists of two-piece construction which seats between the tapered seats in the valve body. This type of wedge is suitable for the treatment of non-condensing gases and liquids at normal temperatures, particularly corrosive liquids.



      Stem of Gate Valve


      The stem, which connects the handwheel and disk with each other, is responsible for the proper positioning of the disk. Stems are usually forged, and connected to the disk by threaded or other techniques. To prevent leakage, in the area of the seal, a fine surface finish of the stem is necessary.

      Gate valves are classified as either based on stems :

      Rising Stem :
      For a valve of the Rising Stem type, the stem will rise above the hand wheel if the valve is opened. This happens, because the stem is threaded and mated with the bushing threads of a Yoke. A Yoke is an integral part from a Rising Stem valve and is mounted to the Bonnet.


      Non Rising Stem :
      For a valve of the non Rising Stem type, there is no upward stem movement if the valve is opened. The stem is threaded into the disk. As the handwheel on the stem is rotated, the disk travels up or down the stem on the threads while the stem remains vertically stationary.









      Sunday, September 27, 2015

      Piping Dimensions (DN Vs NPS)

      The size of pipes, fittings, flanges and valves are given in two Units

      NPS = Nominal Pipe Size (Inches)

      DN = Diameter Nominal (Metric)


      Following is the comparison :

      Diameter Nominal
      DN
      (mm)
      Nominal Pipe Size
      NPS
      (inches)
      6
      1/8
      8
      1/4
      10
      3/8
      15
      1/2
      20
      3/4
      25
      1
      32
      1 1/4
      40
      1 1/2
      50
      2
      65
      2 1/2
      80
      3
      100
      4
      150
      6
      200
      8
      250
      10
      300
      12
      350
      14
      400
      16
      450
      18
      500
      20
      550
      22
      600
      24
      650
      26
      700
      28
      750
      30
      800
      32
      900
      36
      1000
      40
      1050
      42
      1100
      44
      1200
      48
      1300
      52
      1400
      56
      1500
      60
      1600
      64
      1700
      68
      1800
      72
      1900
      76
      2000
      80
      2200
      88
      2400
      96
      2600
      104
      2800
      112
      3000
      120
      3200
      128
        

      Saturday, September 26, 2015

      Valve Fundamentales

      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.


      They perform any of the following functions.

      •  Starting and stopping or isolating fluid flow. In an open valve, fluid flows in a direction from higher pressure to lower pressure. 
      • Controlling or varying (throttling) the amount of fluid flow by change of direction or restriction. 
      • Checking the flow or controlling the direction of fluid flow and preventing backflow.
      • Regulating downstream system or process pressure.
      • Relieving component or piping system of a certain pressure.

      The word is derived from the Latin valva, the moving part of a door, in turn from volvere, to turn, roll.

      Valves may be operated manually, either by a handle, lever, pedal or wheel. Valves may also be automatic, driven by changes in pressure, temperature, or flow. These changes may act upon a diaphragm or a piston which in turn activates the valve, examples of this type of valve found commonly are safety valves fitted to hot water systems or boilers.

      Valves are quite diverse and may be classified into a number of basic types. 

      Classification based on Valve Types :

      Isolation Valves or Block Valves
      • Gate Valves
      • Ball Valves
      • Butterfly Valves
      • Plug Valves

      Non Returning Valves
      • Check Valves

      Controlling or Regulating / Throttling Valves
      • Globe Valves
      • Diaphragm Valves
      • Pinch Valves
      • Needle Valves

      Pressure and Safety Relieve Valves
      • Pressure Reducing Valves
      • Control Valves

      Classification based on how they are actuated :
      • Hydraulic
      • Pneumatic
      • Manual
      • Solenoid Valve
      • Motor

      Classification based on Valve Operating Positions :
      • Two Port Valves
      • Three Port Valves
      • Four Port Valves

      Classification based on Mechanical Motions :
      • Linear Motion Valves
      The valves in which closure member moves in a straight line to allow, stop or throttle the flow.
      • Rotary Motion Valves
      The valves in which the closure member moves along angular or circular path. 
      • Quarter Turn Valves
      Some Rotary Motion Valves requires approximately a Quarter Turn, 0 to 90 Degree, motion of the stem to go fully open from a fully closed position or vice versa.   

      Valve Types
      Linear Motion
      Rotary Motion
      Quarter Turn
      Gate
      YES
      NO
      NO
      Globe
      YES
      NO
      NO
      Plug
      NO
      YES
      YES
      Ball
      NO
      YES
      YES
      Butterfly
      NO
      YES
      YES
      Swing Check
      NO
      YES
      NO
      Diaphragm
      YES
      NO
      NO
      Pinch
      YES
      NO
      NO
      Safety
      YES
      NO
      NO
      Pressure Relief
      YES
      NO
      NO


      Regardless of type, all valves have the following basic parts: the body, bonnet, trim (internal elements), actuator, and packing.


      Valve Components


      Valve Body

      The valve body sometimes called the shell, is the primary boundary of a pressure valve.
      It serves as the main element of a valve assembly because it is the framework that holds all the parts together. 
      The body, the first pressure boundary of a valve, resists fluid pressure loads from connecting piping. It receives inlet and outlet piping through threaded, bolted and welded joints.




      Valve Bonnet

      The cover or opening in the valve body is the bonnet, and it is the second most important part boundary of a pressure valve.
      Bonnet acts as a cover of the valve body, is cast of forged of the same material as of the body. It is commonly connected to body by a threaded, bolted or welded joint.
      During the manufacturing of the valve, the internal components, such as stem, disc etc. are put into the body and then bonnet is attached to hold all the parts together inside.




      Valve Trim

      Valve Trim is the collective name for the replaceable parts, in a valve. A typical trim design includes a disk/wedge, seat, stem and sleeves needed to guide the stem.
      A valve's performance is determined by the disc and seat interface and the relation of the disc position to the seat.
      Because of the trim, basic motions of the flow control are possible.

      Valve Disc

      The disc is the part which allows, throttles, or stops flow depending on its position. In case of a Plug or a Ball Valve, the disc is called a plug or a ball.
      The disc is the third most important primary pressure boundary.
      With the valve closed, full system pressure is applied across the disc, and for this reason the disc is pressure related component.
      Discs are usually forged, and in some designs, hard surfaced to provide good wear properties. Most valves are named by the design of their discs.

      Valve Seat

      The seat or seal rings provide the seating surface for the disc. A valve may have one or more seats.
      In the case of a Globe or a Swing Check valve, there is usually one seat, which forms a seal with the disc to stop the flow.
      In case of Gate valve there are two seats, one on the upstream side and the other on the downstream side. The Valve disc has two seating surfaces, that come in contact with the valve seats to form a seal for stopping the flow.

      Valve Stem

      The valve stem provides the necessary movement to the disc, plug or the ball for opening or closing the valve, and is responsible for proper positioning of the disc. It is connected to the valve hand wheel, actuator, or the lever at one end and at the other end to the valve disc.