In order to simplify the selection and specification of a device with such a broad definition, valves are traditionally classified according to one or more of the following factors
Classifying Valves according to Function
1.On/Off Valves
• Used in applications where media must be diverted, in non-critical mixing, and in safety management systems • Most are hand-operated, although they can be automated with the addition of an actuator as seen in the photo of an Optimux OpTE herein
Common On/Off Valves Include:
• Gate
• Plug
• Ball
• Pressure Relief
2.Non-return valves
Non-return valves allow fluid to flow in only the desired direction; any flow or pressure in the opposite direction is mechanically restricted from occurring • Used to prevent backflow of fluid that could damage equipment or endanger the process • Particularly useful in protecting a pump in liquid applications or a compressor in gas applications
Common Non-Return Valves Include:
• Check valves
3.Throttling valves
Throttling valves are used to regulate the flow, temperature, or pressure of a service; can move to any position within the stroke, including full-open or fullclosed positions
• Can also act as on/off valves • Many are hand-operated, but some are equipped with actuators, which provide greater thrust and positioning capability as well as automatic control
Common Throttling Valves Include:
• Pressure Regulators
• Control Valves
4.Final Control Element
Final Control Element refers to the high-performance equipment needed to provide the power and accuracy to control the flowing medium to specific service conditions
• Part of the control loop, which consists of at least two other elements besides the control valves:
• Sensing element
• Controller
• Control valve makes a change automatically, based on a signal from the controller, and the sensor measures and verifies the change
• Control valves are the most common final control element
Classifying Valves according to Service
General Service
General service valves are those designed for the majority of commonplace applications with lower pressure ratings
• Lower ANSI Class: 150 - 600
• Moderate Temperature: -50 – 650°F
• Noncorrosive fluids
• Minimal Pressure Drops
• No cavitation
• No flashing
• Carbon or Stainless Steel
• Interchangeable and common to a wide variety of applications
Special Service
Special service valves are custom-engineered and designed for a single application outside normal process applications
• High pressures
• Demanding temperatures
• Corrosive fluids
• Minimal to Moderate Pressure Drops
• Mild cavitation
• No flashing
• Special materials
• Unique applications
Severe Service
Severe service valves are fitted with special features to handle extreme applications, such as high pressure drops that result in severe cavitation, flashing, choking, or high noise levels
• High pressures
• Extreme temperatures
• Corrosive fluids
• Severe Pressure Drops
• Cavitation
• Flashing
• Choking
• Noise
• Custom-engineered trims aimed to prevent or reduce effects of service
• Unique applications
Classifying Valves according to Motion
Linear
Linear valves have a sliding-stem that pushes a closure element – any internal device that is used to open, close, or regulate the flow – into an open or closed position
• Simple design
• Easy maintenance
• Versatility in:
• Sizes
• Pressure classes
• Design options
Common linear valve styles:
• Gate
• Globe
• Pinch
• Diaphragm
• Split-body
• Three-way
• Angle
Rotary
Rotary valves use a closure element that rotates – through a quarter-turn or 45° range – to open or block the flow
• Larger port compared to linear valves of similar size
• Weigh less than linear size-for-size
• Limited in applications with pressure drops
• Prone to cavitation and flashing
• Often less costly
Also read
Basics of Control Valves and Parts of Control Valve
To know more about control valves check the link below https://automationforum.co/category/valves/