Valve: types, design, operation and applications

Common types and their roles

Valves are classified by design and function. Familiar examples include:

• Gate valve — primarily used for on/off isolation; low resistance when fully open. See gate valve details.
• Globe valve — suitable for throttling and control because of its flow path; more pressure drop than a gate valve. See globe valve information.
• Ball and plug valves — quarter-turn devices that offer tight shutoff and fast operation.
• Butterfly valve — compact quarter-turn valve used for large-diameter pipelines and low-pressure systems.
• Check valve — prevents reverse flow automatically.
• Safety/relief valve — opens automatically to release excess pressure; essential for protection. Refer to safety valve guidance.

Construction and operation

Most valves share common parts: a body, bonnet or cover, an internal closure element (disc, ball, plug, wafer), a stem connecting the closure to the actuator, seals or seats, and a means of actuation. Actuation methods include manual handles/wheels, electric motors, pneumatic cylinders, or hydraulic actuators. Materials vary by application and include brass, bronze, stainless steel, carbon steel and specialty alloys; material guidance is available at materials and selection.

Applications and selection factors

Valves appear across residential plumbing, water treatment, oil and gas, chemical processing, power generation and HVAC. Choosing a valve requires assessing media type, temperature, pressure, required tightness, frequency of operation, size, maintenance needs and cost. Typical selection criteria are listed below:

• Compatibility with the fluid and temperature
• Pressure rating and leak-tightness
• Flow characteristics and allowable pressure drop
• Actuation method and automation needs
• Maintenance access and expected service life

Maintenance, standards and notable distinctions

Regular inspection and maintenance extend valve life: check sealing surfaces, stems, packing, and actuators; exercise valves periodically to prevent sticking. Many industries follow standards for pressure ratings, testing and markings — consult relevant codes for installation and testing. For installation and piping practices see installation guidance, and for maintenance standards see inspection and testing. Additional technical resources are available at further reading.