Sep. 19, 2022
Globe Control Valve
The globe control valve is used for controlling fluid flow by changing the size of the flow passage according to the controller and enabling direct control over the flow rate. This results in controlling process quantities such as liquid level, temperature, and pressure. In automatic control terminology, it is called the final control element. Based on controller input, globe control valves are able to control fluid flow rates.
Globe control valves can be used to regulate pressure and/or flow rate automatically, no matter which pressure is used. In some cases (as determined by design), different plant systems may operate at pressure and temperature combinations that require Class 300 valves, so all control valves are usually Class 300 for interchangeability. As long as the system does not exceed the rating for the Class 150 valves, this is not necessary.
A control valve can be classified by the mechanical motion of the valve itself. There are two common categories of stem motion; linear and rotary. Both types have their own strengths and weaknesses that are explained below.
The linear-style valve is the most common type of valve available today. It is well-known for its simple design and ease of maintenance. Linear valves, also known as multi-turn valves, have a sliding-stem design that pushes a closure element into an open or closed position. These types of valves are extremely versatile with many different trim sizes and design options available. A linear-motion valve is also more resistant to cavitation compared to a rotary valve. Although linear valves are typically more expensive, they offer precise accuracy and 1:1 linear flow control.
Rotary valves, or quarter-turn valves, have been evolving over the years and are becoming more popular. They use a closure element that rotates, usually through a quarter-turn or 90° range, to block the flow. A rotary-motion valve usually weighs less and is smaller in size than a comparable linear valve. It is also easier to control emissions through the stem packing of a rotary valve without the use of bellows seals. They are less prone to clogging in dirty service applications as well.
It should be noted that rotary valves are limited to certain pressure drops and are known to have cavitation and flashing problems. However, as technology continues to advance, these problems are becoming less common.
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