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.
Ball Valve Design Classification
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.
Multi-port Ball Valve - A multi-port valve is a type of valve which has normally more than two ports and it can have either 3-way, 4-way or 5-way control depending on the application. It is typically used for the selection of several flow paths to enable the process to continue in the manner designed.
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).
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.
Standard Port Ball Valve - A standard port ball valve is about the same diameter as the pipe or tube coming into and exiting it. The working part of the valve is the rotatable ball inside the valve body. Since the working part of the valve fits inside the valve body, the bore through the valve ball is smaller than the diameter of the valve’s connecting pipe or tube.
Trunnion 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.
V-port Ball Valve - A v-port ball valve has either a "v" shaped ball or a "v" shaped seat, which allows the orifice to be opened and closed in a more controlled manner with a closer to linear flow characteristic. This type of valve is also known as a control valve, whereby the flow velocities need to be controlled as required per the application. When the valve is in the closed position and opening is commenced the small end of the "v" is opened first, allowing stable flow control during this stage. This type of design requires a generally more robust construction due to higher velocities of the fluids, which might damage a standard valve. Despite being a control valve, they are not considered to be as accurate as a balancing valve, needle valve, globe valve, or pressure regulating valve.
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 Advantages and Disadvantages
|
|---|
| Advantages | Disadvantages |
|---|
- 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.
|
- 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 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.
|
 |
- Flanged Ball Valves, Full Port
|
|
- Flanged Ball Valves, Standard Port
|
