A ball valve
is a shut-off valve that allows, obstructs, and controls
the flow of liquids, gases, and vapors in a piping system by
rotating the ball having a bore inside the valve. The ball is
mounted against two seats and has a shaft that connects it to
the operating and control mechanism that rotates the ball. When
the cross-section of the bore is perpendicular to the area of
the flow, the fluid is not permitted to pass through the valve.
The fluid flows through from the valve, and the fluid flow rate
depends on the area of the bore exposed to the floor.
Ball valves are a type of quarter-turn valve along with plug
valves and butterfly valves. They can be operated manually or
by using an actuator. The simplest operation of a
floating ball valve is through the use of a wrench
or a lever manually turned by an operator. Torque is applied to
rotate the lever arm by 90° by either clockwise or
counterclockwise to open or close the valve. If the lever arm
is parallel to the pipe, it indicates that the valve is open.
If the lever arm is perpendicular to the pipe, it indicates
that the valve is closed.
Ball valves come in many designs and features to satisfy
various industrial needs. The standards and specifications for
ball valves vary depending on the industry where it is
The ball is a sphere that has a hole in its center. The hole in
its center is called the bore. The bore serves as the flow
opening of the fluid when the cross-section of the fluid flow
path and the bore is coplanar. Otherwise, the flow is
throttled. A ball valve may have a solid ball or a hollow ball.
A solid ball has a constant opening diameter throughout its
structure, which helps the fluid to smoothly flow at a constant
velocity. A hollow ball, on the other hand, has a hollow
internal structure, and the space inside it allows more fluid
to pass through the valve. However, the larger space creates
turbulence and high velocities. A hollow ball is more
lightweight and cheap compared to a solid ball.
The shaft connects the ball to the control mechanism that
rotates the ball. The shaft has seals such as O-rings and
packing rings to seal the shaft and the bonnet to avoid leakage
of the fluid. The shaft may be manually operated by a lever or
a handwheel or operated by an electric, pneumatic, or hydraulic
The bonnet is an extension of the valve housing that contains
and protects the shaft and its packing. It may be welded or
bolted to the body. It is also made of hard metal and it covers
the opening made from connecting the shaft to the external
The valve seats provide sealing between the ball and its body.
The upstream seat is adjacent to the inlet side of the valve.
The downstream seat is found on the opposite side of the
upstream seat which is adjacent to the discharge side of the
A one-piece ball valve has a single-piece cast body that houses
the internal components of the trunnion
mounted ball valve. This eliminates the risk of leakage
of the fluid from the valve. One-piece ball valves are the
cheapest ball valves and always have a reduced bore. A welded
one-piece ball valve is more common but cannot be dismantled
for cleaning and repaired once damaged; therefore, it is only
used for applications with a low possibility of particle
build-up, and where sanitation is not a major concern. On the
other hand, screwed one-piece ball valves can be cleaned,
serviced, and repaired, but dismantling requires special tools.
The floating ball is the most common ball design in ball
valves. The ball is suspended inside the valve and free to move
in a lateral direction when the valve is in a closed position.
It is sandwiched between two seats that support the valve and
hold it in place. The ball is connected to the shaft in a slot
on one end while the other end is free. When the valve is in an
open position, the shaft connection to the slot at the top of
the ball prevents the ball from moving laterally.
The sealing action is only dependent on fluid pressure. During
an operation of a floating ball valve, the inlet pressure of
the fluid forces the ball to the outlet seat which prevents the
fluid from escaping from the valve body. The fluid pressure on
the ball and the seats are higher when the ball valve is in the
Floating ball valves have the simplest design. They come in
smaller diameters and are suitable for liquids and gases
operating under low to moderate pressures. The application of
floating ball valves is limited by the amount of pressure the
seats can handle. At high fluid pressure, the seats can be
deformed from the pressure exerted by the ball which can affect
the sealing characteristics of the valve under low pressure.
Furthermore, the torque to rotate the stem depends on the force
required to counteract the same fluid force acting on the ball
In a trunnion ball valve, the ball is supported by an
additional shaft at its bottom which is called the trunnion.
This holds the ball in its place and limits the movement of the
ball to its axis. The ball can only move if the valve shaft
rotates. Trunnion ball valves also feature spring-loaded seats.
The inlet fluid pressure activates the springs towards the ball
held by the trunnion, which creates a tight sealing.
Trunnion ball valves are available in small to large diameters,
but it is more expensive than floating ball designs. They can
operate efficiently in a wide range of pressures and they are
ideal for high-pressure applications since the fluid pressure
is also dissipated to the trunnion and the springs of the
seats. Hence, they are easier to operate with a lower operating
torque or a small actuator.
A vented ball valve is constructed and operates in the same way
as a standard fully welded ball valve,
except that the vented ball has small orifices drilled into its
side. When the valve is closed, the orifice is directed to the
outlet side of the valve. The drilled hole is used to vent
trapped gases which causes a build-up of internal pressure
inside the valve, to prevent leaking, valve failure, and
Vented ball valves are used in compressed air systems,
cryogenic processing and conveying volatile liquids are also
referred to as the "cryogenic valve" because of their
usefulness in cryogenic processing.
A full bore has a bore diameter similar to the pipe diameter.
The flow area for the fluid for full bore valves remains
constant, therefore the flow resistance offered by this type is
very low. Minimal frictional loss is encountered during fluid
flow; hence the pressure drop is low. A high pressure drop in a
piping system causes pumping more difficult. However, since the
bore diameter should be equal to the pipe size, it requires a
larger ball size and housing which makes it more expensive than
a reduced bore.
Full bore ball valves are easier to maintain and clean. In
pipelines, the pipes are maintained and inspected by an
operation called pigging. A spherical or cylindrical device
called pigs is allowed to flow in the pipes to detect and
remove any build-up without interfering with the fluid inside
the pipeline. This operation is possible with an installed
full-bore ball valve.
Full bore ball valves are also used in conveying liquids with
mixed solids where flow restrictions cause the build-up of
particles that can eventually cause separation of the mixtures
that will flow through it.
A reduced bore has a bore diameter smaller by a pipe size than
the (connection) pipe diameter. The actual reduction is
determined by the agreement between the manufacturer and the
customer. The flow area for the fluid becomes narrower at the
downstream outlet, therefore there are frictional losses that
are introduced which result in a pressure drop. Since the
amount of flow discharge remains constant, the velocity
increases with the decrease in the flow area.
Reduced bore ball valves are more common than full bore ball
valves. They are used in applications where product flow rate
and turbulence are not potential concerns and particle build-up
is not likely to occur. The reduced bore is less expensive than
the full bore since it requires a smaller ball size and
housing. Compared to other types of valves, the reduced bore
ball valves have relatively smaller pressure drop.
A segmented ball valve has a V-shaped notch on its ball. A
segmented 3 way ball valve has good flow rate control
which depends on the ball rotation. Aside from that, it also
has a good shut-off capability. The flow characteristic in a
segment ball valve approaches an equal percentage flow
characteristic. The flow rate in a segmented ball valve
increases exponentially as the ball reaches its fully opened
A cavity-filled ball valve has a seat design that fills the
gap between the ball and its body. This eliminates the
possibility of entrapped media or particle build-up over time
around the ball which can cause contamination or blocking of
the fluid flow. Cavity-filled ball valves are easier to clean
Cavity-filled ball valves are valuable in industries where
sanitation is crucial, such as in food, pharmaceutical, and
bioprocessing industries. They are ideal in handling solid-
liquid mixtures such as slurries.
Multi-port ball valves are used in diverting, combining,
splitting, or shutting off multiple fluid streams through the
use of a ball with an L-shaped or T-shaped bore segmented
through its middle. A flow upstream to the inlet of a multi-
port valve can be split into multiple outlet streams. It can
split a flow, but cannot distribute the flow to its outlet
streams in pre-determined flow rates. It can also join multiple
flow streams into a single stream, or simply change the
direction of the fluid flow. The schematic diagram below shows
possible flow configurations of an L-shaped and a T-shaped
multi-port ball valve.
Brass is an alloy of copper and zinc that can be distinguished
by its dull yellowish to reddish color, depending on the amount
of zinc. It is the most common material for ball valves. Brass
is a tough, strong, and durable metal that can withstand high
temperatures and pressures. The copper in brass alloy has
antimicrobial properties that inhibit the growth and
reproduction of microbes on its surface. Brass has good
chemical, corrosion, and biofouling resistance. It is inert to
most acids, alkalis, and bases, except for solutions with high
chlorine content. Chlorine can cause dezincification, a
reaction where chloride ions strip away zinc from the alloy,
causing a porous structure. Dezincification can drastically
reduce the strength of the material.
- Created: 30-12-21
- Last Login: 30-12-21