|
درباره:
|
What is a Ball Valve and How Does It Work?
</p>
<p>
A <a href="http://www.highmpa-valve.com/ball-valve/" target="_self">ball valve</a>
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.
</p>
<p>
<br/>
</p>
<p>
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 <a href="http://www.highmpa-valve.com/ball-valve/floating-ball-valve/"
target="_self">floating ball valve</a> 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.
</p>
<p>
<br/>
</p>
<p>
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 utilized.
</p>
<p>
<br/>
</p>
<p>
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.
</p>
<p>
<br/>
</p>
<p>
Shaft
</p>
<p>
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 actuation.
</p>
<p>
<br/>
</p>
<p>
Bonnet
</p>
<p>
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 control
mechanism.
</p>
<p>
<br/>
</p>
<p>
Seat
</p>
<p>
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
valve.
</p>
<p>
<br/>
</p>
<p>
A one-piece ball valve has a single-piece cast body that houses the internal
components of the <a href="http://www.highmpa-valve.com/ball-valve/trunnion-mounted-
ball-valve/" target="_self">trunnion mounted ball valve</a>. 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.
</p>
<p>
<br/>
</p>
<p>
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.
</p>
<p>
<br/>
</p>
<p>
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 closed position.
</p>
|
