Ball Valve

Written by Matt Milbury on . Posted in Valve

A ball valve, abbreviated as BV, is a quarter turn valve used for changing the direction of a process stream (divert or shut off).  Ball valves can be automated to automatically shutdown or open depending on the orientation of the actuator.  True ball valves should not be used as control valves as velocities between the ball and seat can be high enough to wash out the sealing portion of the valve.  The ball on the valve can be characterized to act as a control valve such as a V-ball type design.

 

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 Ball Valve Types

  • Metal Seated Ball Valve  -  Metal seated ball valves are described as extreme service valves.  They are called metal seated ball valves because the ball and the seat are made out of metal.  These are typically seen in high pressure & high temperature applications such as steam in a power generation plant.  Metal seated valves are high torque valves due to the high pressure differential across the valve and the metal ball and seat.  In order to completely seal, the seat must be machined to exactly match the ball.  If there is any misalignment of the ball, the valve will leak.  This is because the metal seat is less forgiving and less pliable than soft seated valves.
  • Reduced Port Ball Valve  -  Reduced (standard or regular) bore valve has a smaller bore diameter in the ball than the internal diameter of the pipe.
  • b00705Trunnion Mounted BaTrunnion Ball Valve  -  Trunnion design is simply the use of upper and lower supports to retain the ball under pressure.  Named for the "trunnion" historically used to support a cannon, a ball valve trunnion essentially doubles the safety and usability of a ball valve.  Another important benefit of the trunnion design is that it allows the ball valve to act as a true union.  The downstream piping can be disconnected under full upstream pressure (user is responsible to ensure that downstream piping is drained of liquid and that valve is indeed closed and secured to upstream piping).  The trunnion on a two-way ball valve supports the ball in much the same way as the stem does at the top. The trunnion on a three-way ball valve is a much different design, being more like a supporting ring, but provides the exact same function and inherent stability.
  • Non-Trunion (Floating) Ball Valve  -  Floating ball valves are used in low pressure or small bore processes.  A floating ball valve has two seats, located upstream and downstream of the ball.  When the valve is closed, pressure differential across the valve assists in seating the ball.  The adjacent ball valve is a ANSI 300 8" soft seated floating ball valve with manual actuator (handwheel).

 

 

Ball Valve Advantages

  • Since the ball valve is a quarter turn valve, it is very easy to automate.
  • It can achieve fast opening and closing.
  • It has the lowest flow resistance.
  • They have a low pressure drop and relatively high flow capacity due to the opening size in the ball.
  • When fully open, there is little turbulence or resistance to the fluid flow.
  • It can be reliably used in corrosive media and low boiling liquids because it will not get stuck during work with the absence of lubricant.
  • The medium is sealed reliably on both sides.
  • It can achieve complete sealing within a large pressure and temperature range.
  • When fully open and fully closed, the sealing surface of the ball and the valve seat is isolated from.
  • When the medium passing through the valve at high speed, it does not cause erosion of the sealing surface.
  • The valve body is symmetrical, especially the welded valve body structure, so it can well withstand the stress from the pipeline.
  • Has a compact structure and is lightweight.
  • Has a longer life span, it is an ideal valve for oil and natural gas pipelines.
  • In large applications, a ball valve may be economically prohibitive.  This is due to the amount of metal that makes up the body and ball.

 

Ball Valve Disadvantages

  • They are not suitable for slurry type applications due to cavities around the ball and seats.
  • Due to its widespread use, the ball valve is considered a commodity item and can be found at most piping supply shops.
  • Slurries or other thick liquids tend to solidify or clog inside of the cavities, greatly increasing the operating torque of the valve and in some cases rendering the valve inoperable.
  • They should only be used in either the fully open or closed position and should not be used for long term throttling.
  • They have a limited accuracy in controlling the flow rate.
  • Operating for extended periods in a partially open position will result in the soft seals of the valve deforming around the edges.
  • The main valve seat seal material of is Teflon, which has a high coefficient of expansion, sensitivity to cold flow and poor thermal conductivity.
  • For large diameter applications that require a quarter turn valve, a butterfly valve may be appropriate.

 

Ball Valve Bore Size

The bore of a ball valve is the area through which the fluid flows.

  • Full Bore  -  A full bore valve has an opening that is equal to the nominal pipe size (NPS) of the flowing pipe.  These valves are the ideal solution where pressure drop is a concern.  Full bore valves are the ideal choice where pigging of process lines is a major consideration.  Normal "dumb" pigs may be able to deform across a reduced bore ball valve.  Smart pigs, however cannot.  Full port valves are normally used when inserting sample probes, injection quills or interface probes to facilitate removing the device from the system while under full line pressure.
  • Standard Bore  -  A standard bore ball valve typically has an area that is equal to the NPS of the pipe one size smaller than the flowing line.  

 

Ball Valve standards

API Standards

  • API Spec 6D - Specification for Pipeline Valves, End Closures, Connectors and Swivels
  • API Std 598 - Valve Inspection and Test

ASME Standards

  • ASME B16.5 - Pipe Flanges and Flanged Fittings: NPS 1/2 through 24
  • ASME B16.10 - Face to Face and End to End Dimensions of Valves
  • ASME B16.20 - Metallic Gaskets for Pipe Flanges: Ring-Joint, Spiral-Wound, and Jacketed
  • ASME B16.25 - Buttwelding Ends
  • ASME B16.34 - Valves Flanged, Threaded and Welding End

BSI Standards

  • BS 2080 - Specification for face-to-face, centre-to-face, end-to-end and centre-to-end dimensions of valves
  • BS 5159 - Specification for cast iron and carbon steel ball valves for general purposes
  • BS 5351 - Specification for steel ball valves for the petroleum, petrochemical and allied industries

ISO Standards

  • ISO 7121 - Steel ball valves for general-purpose industrial applications

MSS Standards

  • MSS-SP-61 - Pressure Testing of Steel Valves
  • MSS-SP-72 - Ball Valves with Flanged or Butt-Welding Ends for General Service
  • MSS-SP-84 - Steel Valves, Socket Welding and Threaded Ends

 

Ball Valve Datasheets

Face to face dimensions for full and standard port valves is the same.  All ball valves 2" and below are both standard and full port valves.

data flg ball valve 1 data flg ball valve 1

 

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Tags: Valves Types of Advantages and Disadvantages