Different Types of Control Valve

 

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Topic: Different Types of Control Valve

 

Ø What is control valve?

A control valve is a control device used to manage and direct the flow of fluids by varying the size of the flow passage. It gives the direct control of flow, temperature, pressure or liquid level Control valves regulate the flow of a liquid or gas by opening or closing internal passages. The control valves gives the respond to instructions from the controller and then adjust the internal openings accordingly. It varies the rate of flow passing through itself i.e the valve. The valve stem moves, altering the size of the passage and this increases decreases or holds steady the flow. The control valve opening is altered whenever the process parameter being controlled does not equal the value it is meant to be the set point.

A control valve consists of three main parts in which each part exist in several types and designs - Valve’s actuator, Valve’s positioner and Valve’s body.

 

Ø Types of Control valve

 

1.   Globe control valves:

 

     A globe valve is one of the most common types of control valve. Globe Control valve are widely used for control systems with precise regulation qualities. Their characteristics can be customized by the condition, and it can be safe and reliable handling of high differential pressure. For high-pressure drop application, we use a multi-stage design to relieve the outlet pressure and also with low noise internals. The globe control valves required low actuator forces but can achieve low leakage even complete tightness function. Also no worry with the high switching cycle on the site. Of course, the control valves have disadvantages such as large install space and low flow capacity.

Globe valves have sphere-shaped bodies. Inside the valve, a baffle separates two halves. This internal structure creates a different flow path than ball valves and other rotary-type valves. Globe valves actuate in a linear movement.

It is used in Oil and gas producers to control the flow, pressure and temperature of process fluid, water, or gas. Producers can control globe valves with mechanical, pneumatic, or electric power. Depending on the type, the valve can provide either on/off or throttling service.

The valves may be equipped with pneumatic spring diaphragm, Piston single or double effect pneumatic actuators can be supplied for special shutoff pressures and electrical actuators.

 

 

2.   Angle type control valves

 

     Angle valves are structured so that the center lines of the entrance and exit of the fluid intersect perpendicularly. In general, the horizontal line is the entrance and the vertical line is the exit.
This structure allows the fluids commonly known as slurry i.e. viscous fluids and fluids including solid bodies to pass more easily through the valve, making it suitable for controlling them. Additionally, it prevents the valve from being damaged due to fluid cavitation and flashing, making it suitable for fluids with these conditions.
This valve type is mainly adopted to solve problems that are difficult to address with general-purpose valves. Therefore, we can apply various materials e.g., ceramic and cemented carbide to the trim parts and its peripheral parts in order to handle special needs.

Angle control valve design the inlet and outlet are perpendicular to each other. It uses linear motion to move the closure part in and out of the base surface. Angle control valves are usually used for boiler feed water and heater blow down services, and in piping systems where space is limited and pipe valves can also be used as elbows. The valve can adopt a cage structure or an extended outlet connection, restricted internals, or outlet linings to reduce corrosion, flashing or cavitation damage.

 

 

3.   Diaphragm type control valves

The diaphragm type control valves consisting of three main components: the body, the diaphragm, and the actuator.

The diaphragm is a dynamic component that restricts or isolates the flow of the medium. The original valve design includes a “weir” on the valve body, the medium flows through the weir, and the diaphragm seals. A straight-through design was introduced to handle solid particles. Both designs can utilize a variety of different diaphragm and liner materials.

 

4.   Ball type control valves

 

     The V-Port or segmented ball is the most common type for ball control valves. Ball valves are widely used in fluid systems in many industries due to their low cost, durability, and excellent closing performance. Similar to butterfly valves, they are not as effective in flow control applications that require high precision and control sensitivity. One of the reasons is that the ball valve requires high torque to open and close, which prevents the operator from making fine adjustments. There is also a certain gap between the stem and the ball, which makes it difficult to find a specific flow rate suitable for fluid control applications.