A valve is a piping system component that controls the flow of media through the system.
This is accomplished through the manipulation of an obstructer within the valve.
Actuated valves use mechanical devices known as “actuators” to control the valve with a power source such as compressed air or electricity.
Most actuated valves are also available in a manually operated version or with a manual override.
All of the most common types of automated valves are classified into one of three groups: self-actuated, linear and rotational.
Within each of these categories, there are various valve types, each with its own set of advantages.
Rotary valves
Rotary valves are also known as “quarter-turn” valves.
Quarter-turn valves provide a full range of motion with a 90-degree handle turn.
This makes them ideal for situations where speed and ease of opening and closing are more important than precision.
It includes:
Ball valves
Quarter-turn by far the most common type of process control valve is the two-way ball valve.
They are two-way (inlet and outlet) and two-position (open and closed) valves used to shut down or isolate a system, or a loop or component within a system.
A ball valve’s basic design includes a ball as the obstructer sandwiched between two cup-shaped seals known as “seats.”
Typically, the ball has a straight bore through it.
When the valve is open, media flows through this bore.
When the ball is rotated 90 degrees, the flow of media is halted by the ball’s sides, which now fill the opening in the seats.
They work best in on/off applications.
Throttling is possible, but it is not a good application for most standard ball valves.
Throttling can be accomplished with specialized ball valves.
Plug valves
Except for the shape of the obstructer used, the basic construction of a plug valve is nearly identical to that of a ball valve.
A slightly tapered cylinder replaces the ball in this case.
This cylinder, like a ball valve, has a bore through it and operates in the same manner, being open in one position and closed when rotated 90 degrees.
Plug valves have advantages that make them the preferred choice in certain applications.
One advantage is that they have no voids or cavities where media can become trapped.
Another advantage is that they can be adjusted to repair leaks that may develop over time, whereas ball valves must be repaired or replaced.
Plug valves, like ball valves, are typically used for on/off applications.
They are oftenused in corrosive environments, such as those found in refineries and chemical plants.
Butterfly valves
Butterfly valves, as opposed to the ball and plug valves, use a disc-shaped obstructer.
“Resilient seated” butterfly valves are the most basic, general-purpose butterfly valves.
They have a single seal ring that serves as both a seal between the valve body and the disc and a seal between the pipe flanges and the valve body.
The flow is stopped when the disc is perpendicular to the direction of flow.
When the valve is rotated 90 degrees, the flow travels around the disc’s slim profile, passing through the valve.
They are often used on larger pipe sizes where a ball or plug valve would become too large, expensive and heavy.
They can also be used as a flow control valve or an on/off valve.
When using a manual actuator in a flow control application, it must lock into place so that the fluid force does not rotate the disc in either direction.
This feature is present in the majority of manual butterfly valves.
Linear valves (multi-turn)
They are classified into two types: rising stem (multi-turn) and axial.
While both valve types rely on the linear motion of the flow obstructer, their construction and operation are very different.
In multi-turn rising stem valves, the obstructer is moved by the rotation of a threaded rod (stem) attached to the obstructer.
Multi-turn valves include gate valves, globe valves, pinch valves, diaphragm valves and needle valves.
These valves are common in flow control applications.
Axial valves use pneumatic or electromagnetic force to move the obstructer along an axis which includes coaxial valves and angle seat valves.
These valves are typically fast-acting and are only used for on/off process applications.
Rising stem (multi-turn)
Gate valves
In general, a gate valve is used to completely shut off fluid flow or, when fully open, to provide full flow in a pipeline.
As a result, it can be used in either the fully closed or fully open position.
They are made up of a valve body, seat and disc, a spindle, gland, and a wheel that is used to operate the valve.
The seat and the gate work together to stop the flow of fluid.
Globe valves
Globe valves are commonly used in plant piping because of their outside shape.
They can be operated manually or automatically.
In contrast to the gate valve, the globe valve can be used to regulate flow or pressures as well as completely shut off flow.
It can also function as a pressure relief valve or a check valve.
The globe valve has significantly higher-pressure loss in the fully open position when compared to a gate valve or ball valve.
This is because the flow of fluid changes direction as it passes through the valve.
This type of valve has an L/D ratio of about 340.
They are available in sizes ranging from NPS 1 to NPS 16.
They are typically operated by a handwheel.
Needle valves
For one thing, they are smaller and allow for finer flow control on smaller lines.
Instead of a disc-shaped plug, they employ a “needle” with a conical shape that moves in and out of an orifice.
While useful as an on/off switch, these are not the best option.
Needle valves are designed for precise flow control.
References
[1] Provider, A., n.d. Types of Valves. [online] Assured Automation. Available at: <https://assuredautomation.com/actuated-valve-training/types-of-valves.php> [Accessed 11 March 2022].
[2] Bajpai, P., 2018. Biermann’s Handbook of Pulp and Paper. San Diego: Elsevier.
[3] Ratnayaka, D., Brandt, M. and Johnson, M., 2009. Water Supply. Burlington: Elsevier.
