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CONSTRUCTION OF BALL VALVE
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Parts of a Ball Valve
Ball valves are constructed with several crucial components:
- Valve Body
This is the main part of the valve and contains all of the components for on/off control. - Rotary Ball
The ball is designed with a center bore (hole) that the media flows through. The direction of the ball is controlled by turning the stem. - Stem
This connects the ball to the external control mechanism. For example, in a manual ball valve the stem is connected to a handle or lever. - Seats
These are discs that lie in between the body and the ball. Seats provide a seal between the two and also support the ball. - Power Source
The stem of the ball valve is rotated using manual or actuated power sources. Manual actuation includes levers and handles that are controlled by an operator. Automated power sources like electric, pneumatic and hydraulic actuation are also available. - Packing
This is a seal around the stem that prevents the media from escaping. - Bonnet
The bonnet is the part of the body that contains the stem and packing.
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Valve Body Construction
- 1-Piece Ball Valves
This design features a single, solid cast body. Since 1-piece ball valves are not designed to be easily repaired, these are often considered “throwaway” valves.
- 2-Piece Ball Valves This design consists of the main body and one end connection. Two-piece ball valves can be repaired if removed from service. However, repairs can be difficult because galling can occur in the threads when the end plug is removed from the valve body.
- 3-Piece Ball Valves
A 3-piece ball valve features a main body and two pipe connectors, which are threaded or welded to a pipe. The main body can be easily removed for cleaning or repairs, without removing the pipe connectors.
Valve Body Styles
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There are three different types of valve body styles, as defined by Piping Guide:
- Split-Body Ball Valve
This design features a two-part body that is held together by a flange connection. One body part is smaller than the other, and the ball is inserted into the larger part. - Top-Entry Ball Valve
Top-entry designs allow you to remove the top of the valve to access the interior for assembly, disassembly, repair and maintenance. - End-Entry Ball Valves
These ball valves have a single main body, and the ball is inserted through one end.
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Ball Designs
There are two main types of ball designs: floating and trunnion. Floating is the most common design, while trunnion balls are often more expensive.
Floating balls are supported by cupped seats to create a tight seal between the body and the ball. Trunnion balls work similarly to floating balls, only the seats are spring loaded and the ball only rotates on its axis. The operating torque is generally lower for trunnion valves.
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Ball Valve Hole Designs
The hole in the ball can be designed using three different profiles:
- Full Bore
A full bore design is also called a full port design. The bore diameter is the same diameter as the pipe, which reduces friction losses and makes the valve easier to clean. - Reduce Bore
A reduced bore design is what you will find in most ball valves. This design has a smaller diameter than a full bore and may introduce small losses of friction. - V-Shaped
The hole in the ball or the valve seat can also have a V-shaped design. V-shaped bores can more precisely control flow rate when rotating the ball. - Vented
A vented ball valve has a small hole drilled into the upstream side. This hole eliminates unwanted pressure within the valve.
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End Connections
There are three common ways to connect a ball valve to a piping system:
- Threaded
Threaded end connections can either be female or male. A female threaded end connection on a ball valve will fit with a male threaded pipe, and vice versa. There are also ball valves that come with one female and one male end connection. - Flanged
Flanged ball valves have bolt holes on the end connectors to attach to the matching flanges on a pipe.
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1 Comments
Great article.
ReplyDeleteJust missed was to include the ball valves with an integral ball and stem design, in which the body is called split in symmetrical shape.
Is a design in which the stem is integral with the sphere, forming a single piece.
In this ball valve design, the occurrence of hysteresis is virtually eliminated and is more likely to occur in floating ball or trunnion designs due to the clearance between the stem and ball. Due to the absence of hysteresis, ball valves of integral stem and ball design are widely applied where precision in ball movement according to the electrical or pneumatic signal received from the panel is desired.
The integral ball and stem type ball valve model can also be called a pendulum type due to the "pendulum" movement of the ball during its opening and closing movements, in addition to the movement itself caused by the fluid pressure when pushing the ball against the ring downstream.