| Ball Valve | A spherical closure element rotates approximately 90 degrees. A drilled passage aligns with the pipeline to permit flow and turns perpendicular to the pipeline to stop flow. | Body, ball, stem, seats, bonnet or cover, and handle or actuator. | Excellent on/off isolation. Standard designs are not intended for precise throttling because partially open operation may cause seat wear and turbulence. | Water systems, compressed air, gas service, process isolation, and general industrial piping. | Media compatibility, pressure and temperature ratings, seat material, bore size, required shutoff performance, and actuation method. |
| Butterfly Valve | A circular disc rotates around a shaft located in or near the pipe centerline. The disc position changes the open flow area. | Body, disc, shaft, seat, liner, and manual or automated actuator. | Suitable for isolation and moderate throttling. Pressure loss is generally low when fully open. | Large-diameter water, HVAC, wastewater, fire protection, and industrial process lines. | Pipe diameter, disc and seat materials, pressure class, available installation space, flow velocity, and shutoff requirements. |
| Gate Valve | A wedge or slab-shaped gate moves linearly into or out of the flow path, usually by turning a threaded stem. | Body, gate, stem, bonnet, seats, packing, and handwheel or actuator. | Designed mainly for fully open or fully closed service. It normally provides low resistance when fully open but is unsuitable for routine throttling. | Water distribution, pipelines, utility services, and applications requiring infrequent isolation. | Media cleanliness, pressure rating, stem arrangement, installation orientation, space for vertical travel, and sealing requirements. |
| Globe Valve | A movable plug or disc travels toward or away from a stationary seat. The changing opening regulates the flow path. | Body, plug or disc, seat, stem, bonnet, packing, and actuator or handwheel. | Good throttling capability and controllability, but usually higher pressure loss than straight-through valve designs. | Steam, cooling water, fuel systems, and process lines requiring frequent adjustment of flow. | Required flow coefficient, pressure drop, temperature, trim material, cavitation risk, and actuator force. |
| Check Valve | Fluid pressure opens the closure element in the permitted direction. Reverse flow causes the element to close automatically. | Body, disc, piston, ball, spring, hinge, seat, and cover, depending on the design. | Provides automatic one-way flow protection rather than operator-controlled regulation. | Pump discharge lines, compressor systems, water systems, chemical process piping, and backflow prevention. | Minimum opening pressure, reverse-flow conditions, closing speed, water-hammer risk, orientation, and media compatibility. |
| Needle Valve | A tapered needle moves into a small seat opening, allowing very fine adjustment of the flow passage. | Body, tapered stem or needle, seat, bonnet, packing, and handwheel. | Very precise low-flow regulation, normally with relatively high pressure loss. | Instrumentation lines, laboratory equipment, calibration systems, sampling lines, and hydraulic control circuits. | Required low-flow range, adjustment resolution, pressure rating, temperature, leakage class, and particulate content. |
| Plug Valve | A cylindrical or conical plug rotates inside the valve body. A passage through the plug aligns with the pipe when open. | Body, plug, stem, sleeve or seat, packing, and actuator or handle. | Primarily used for rapid isolation; some lined or specialized designs can support throttling. | Gas, liquid, slurry, wastewater, and process systems requiring compact quarter-turn operation. | Media abrasiveness, lubrication requirements, sealing design, pressure drop, temperature, and torque demand. |
| Pressure-Reducing Valve | A spring-loaded or pilot-operated mechanism senses downstream pressure and changes the opening to maintain a lower target pressure. | Body, main disc, seat, diaphragm or piston, spring, sensing passage, and adjustment mechanism. | Automatically regulates downstream pressure despite changes in inlet pressure or demand within its operating range. | Building water systems, compressed air, steam distribution, irrigation, and process utilities. | Inlet and outlet pressure, flow range, set pressure, pressure drop, response speed, and risk of cavitation. |
| Flow Control Valve | An actuator positions a closure element according to a control signal from a controller, changing the effective flow area. | Valve body, trim, plug or disc, stem or shaft, actuator, positioner, and feedback components. | Continuous modulation of flow using pneumatic, electric, or hydraulic actuation. | Process control, temperature loops, chemical dosing, boiler systems, and automated fluid handling. | Required flow coefficient, rangeability, fail position, signal type, actuator sizing, noise, cavitation, and process dynamics. |
| Relief Valve | The valve opens automatically when system pressure reaches a predetermined set pressure and closes after pressure is reduced. | Body, nozzle, disc, spring, adjusting screw, bonnet, and sealing surfaces. | Protects equipment from excessive pressure; it is not normally used for routine flow regulation. | Pressure vessels, boilers, piping systems, pumps, compressors, and hydraulic equipment. | Set pressure, relieving capacity, accumulation limits, discharge routing, back pressure, temperature, and fluid phase. |