Essential Control Valve Parts

Posted: 2017-10-27 12:40:44

Control Valve Parts 101

Control valves are valves used to control flow, pressure, temperature, and liquid level by opening or closing in response to signals from controllers and sensors monitoring the relevant conditions. Also known as final control elements, control valves are used in a huge variety of purposes across many technologically advanced industries. They consist of three main parts although the final arrangement and design of these pieces differs greatly between types of valve.

Actuator
The actuator is the part of the valve physically responsible for the opening and closing of the valve. Depending on the type of valve, actuators may be electrical, hydraulic, or pneumatically operated.
Positioner

The positioner is the part of the valve that receives electric or pneumatic signals from relevant sensors and controls the automatic opening or closing of the actuator accordingly. There are a variety of common signal types depending on the application of the control valve. These include new Smart systems such as the HART, Fieldbus Foundation, and Profibus systems as well as the industry standard 4-20mA signals, and the standardized 0-10V HVAC signals.

Body

Because there are many different applications for control valves, there are also many different kinds. Each type of control valve has a slightly different body designed to suit its particular purpose.

Angle Seat Valves

Pneumatically controlled, these valves include a piston actuator which provides linear actuation, lifting a seal off its seat. The seat is angled to allow for the largest possible maximum flow when open. These valves are well suited for applications with large flowrates or environments with chronically high temperatures.

Globe Valves

Once named for the spherical shape, globe valves are typically no longer designed in a globular shape. Used to regulate flow within a pipeline, they consist of two halves which are separated by an internal baffle in which an opening forms the seat for the seal. With this type a movable plug is screwed in to close the valve.

Diaphragm

Valves Constructed of metal or plastic, diaphragm valves were once designed for industrial applications, but now see more use in bio-pharmaceutical applications. Manually or automatically operated, they consist of a body with two or more parts, a diaphragm, and a weir or seat on which the diaphragm sits in order to close the valve. Rotary / Butterfly Valves Often used for regulating or isolating flow, these valves are similar in function to ball valves in that they allow for quick shut off when necessary. Lower in cost and lighter in design than many other types, they are a popular choice for many applications, but do result in a permanent pressure drop due to their position within the pipe. These valves consist of a disc located within the flow that can be moved parallel or perpendicular to the flow in order to open or close the valve.

Rotary / Butterfly Valves

Often used for regulating or isolating flow, these valves are similar in function to ball valves in that they allow for quick shut off when necessary. Lower in cost and lighter in design than many other types, they are a popular choice for many applications, but do result in a permanent pressure drop due to their position within the pipe.

These valves consist of a disc located within the flow that can be moved parallel or perpendicular to the flow in order to open or close the valve.