For anyone new to waterworks valves – or for those who simply want a quick refresher on the common terms used in our industry – we’ve put together this comprehensive list of terms and brief definitions. It’s a quick and easy way to get an overview of important valve terminology, and a valuable reference to use any time you come across a term you’re just not familiar with.
Accumulator – A pressure vessel used to store fluid under pressure for future use, typically to maintain pressure, absorb shocks, or provide emergency power.
Actuator – A mechanical device that moves or controls a mechanism or system; in valves, it opens or closes the valve via electric, pneumatic, or hydraulic power.
Allowable Leakage (Rate) – The maximum allowable leakage past a valve seat. Typically following a standard for each valve type, set by industry associations such as the American Water Works Association.
Anti-Cavitation Trim – Reduces or eliminates cavitation damage in control valves.
Bi-Directional – A valve that can effectively seal in both directions, allowing flow from either side.
Blind Flange – A solid disk used to close the end of a pipe or valve opening.
Blowout Proof Stem – A design preventing stem ejection under pressure.
Bolted Bonnet – A valve bonnet (cover) that is bolted to the body, allowing easy removal for maintenance.
Bonnet – The part of the valve that covers the opening in the valve body through which the stem passes.
Bonnet Extension – A combination of an outer support tube and an inner torque tube that extend the actuator mounting flange and valve stem away from the valve.
Bore (Port) – The internal diameter of the valve through which fluid passes.
Buried Service – Refers to valves installed underground, typically requiring extended stems or operators.
Burst Pressure – The internal pressure at which a valve or pipe will rupture or fail.
Butt Weld Ends – Valve ends prepared for welding directly to piping, ideal for high-pressure service.
Bypass – A secondary flow path used to relieve pressure, preheat lines, or balance systems.
Caged Trim – A control valve feature that reduces noise and vibration.
Casting Number / Heat Number – Identifiers for material traceability.
Cavitation – The formation and collapse of vapor bubbles in liquid flow, potentially causing damage to valve internals.
Chevron Packing – V-shaped rings used in sets for sealing valve stems or pistons.
Closure Element – The part of a valve (e.g., ball, gate, plug) that stops or permits flow.
Curb Box - A enclosure used to protect a valve, an actuator, or drive nut from damage or contamination. Typically includes a lid that allows easy access to the actuator drive nut from a sidewalk or curb.
Cv – Flow coefficient; a measure of a valve’s capacity to pass flow.
CWP – Cold Working Pressure; the maximum pressure a valve can withstand at ambient temperature.
Dead Tight – A very high degree of sealing, implying zero leakage.
Design Pressure – The maximum pressure a component is designed to handle during normal operation.
Differential Pressure – The difference in pressure between the inlet and outlet of a valve.
Dip Tube – A tube extending into a vessel to direct flow or draw fluid from a specific level.
Double Block and Bleed – A valve configuration that isolates both sides of a line and bleeds the space between for safety.
Double Offset – Design used in butterfly valves to reduce seat wear by offsetting the disc centerline from the body centerline in 2 directions.
Drip Tight – Indicates no visible drips or leakage under test conditions.
Elastomer - A natural or synthetic polymer having elastic properties, e.g. rubber.
End Connection – The type of connection (e.g., flanged, threaded, welded) used to attach the valve to piping.
Equivalent Pipe Length – A method of expressing valve pressure drop as an equivalent length of straight pipe.
Expansion Joint – A flexible component that absorbs thermal expansion or movement in piping.
Extended Bonnet – A bonnet extension used for insulation or cryogenic service.
Extension Stem – A shaft used to extend a valve stem or actuator drive nut. Typically used for buried or hard-to-reach valves.
Face to Face – The dimension between the inlet and outlet faces of a valve.
Facing – The finish or treatment on the sealing face of a flange.
Feet of Head – A unit of pressure representing the height of a fluid column.
Fire Safe – A valve that maintains tight shutoff during or after exposure to fire.
Flange – A flat surface for connecting valves to pipes using bolts.
Flat Face – A flange face without a raised surface, used for low-pressure applications.
Floating Ball – A ball valve design where the ball floats to press against the downstream seat for sealing.
Floor Box – A tube with cover, typically installed in a concrete floor, that protects an operating nut.
Floorstand – A stand used to mount a valve actuator in an elevated position for ease of access, ergonomics, or safety.
Flow Characteristic – Defines how valve opening relates to flow rate (e.g., linear, equal percentage, quick opening).
FOG – Fat, Oil, and Grease in waste systems.
Full Port/Bore – A valve with a bore equal to the pipe diameter, offering minimal flow restriction.
Gasket – A sealing material placed between flanges to prevent leakage.
Gland – A component that compresses packing to create a seal around the valve stem.
Gland Flange/Follower – A part that compresses the packing gland to maintain stem sealing.
Grease Fitting – Allows lubrication of valve internals.
Grooved End – A piping connection with grooves that allow coupling with clamps.
Hastelloy – High-performance alloy for corrosive service.
Hot Tap – A method for connecting to a pressurized system without shutdown.
Hydrostatic Test – A pressure test using water to check valve integrity and leaks.
Hysteresis – The lag between input and movement in control valves.
Lip Seal – A seal with a flexible lip that contacts a shaft or surface to prevent leakage.
Low Emission Packing – Stem packing designed to minimize fugitive emissions.
Lube Seats – Valve seats designed to accept grease for lubrication and sealing.
Manhole – A small vault or vertical shaft, covered with a heavy lid, providing a person access to a valve or pipeline. Typically buried underground.
Mechanical Seal – A sealing device for rotating shafts to prevent leakage.
Media – The fluid (liquid, gas, slurry) that flows through a valve.
Metal to Metal Seal – A seal formed by metal contact rather than elastomeric materials.
Neck – The elongated portion of the valve body leading to the actuator or operator.
Neck Extension - A combination of an outer support tube and an inner torque tube that extends the actuator’s mounting flange and valve stem away from the valve.
Nipple – A short length of pipe with male threads on both ends.
Oxygen Cleaning/Service – Special cleaning and materials to prevent ignition in oxygen-rich environments.
Packing – Material used to seal the valve stem against leakage.
PIG (Pipeline Inspection Gauge) – A device used to clean or inspect pipelines internally.
Piston Effect – A pressure phenomenon where force acts on one side of a closure element.
Port – The opening in the valve body that allows fluid flow.
Pressure Class – The pressure rating system for valves based on ANSI or API standards.
Pressure Envelope – Parts of the valve that contain system pressure.
PTFE (Teflon) – A common seat or seal material with high chemical resistance.
Purge Port – Used for cleaning or draining the valve cavity.
Quarter-Turn Valve – Requires a 90° rotation from fully open to fully closed.
Raised Face – A flange face with a raised sealing surface to concentrate gasket pressure.
Rangeability – The ratio of max to min controllable flow in a control valve.
Reducer – A fitting used to connect pipes and valves of different diameters
Resilient Seat – A valve seat made from elastomeric material to provide tight shut-off.
Riser – A vertical pipe or conduit used in plumbing and fire protection.
RTJ – Ring Type Joint; a high-pressure flange design using a metal gasket.
Seat – The surface inside a valve where the closure element seals against.
Shell Test – A pressure test of the valve body to ensure structural integrity.
Shell Wall Thickness – Wall thickness of valve body as per design pressure requirements.
Shutoff Class – Leak rate rating (e.g., Class VI means bubble-tight shutoff).
Slip On Flange – A flange that slips over the pipe and is welded into place.
Socket Weld Ends – A welding end for small-diameter, high-pressure applications.
Standard Port – A valve with a port size smaller than full bore but larger than reduced port.
Threaded Connections – Threaded ends (e.g., NPT, BSP) for smaller or low-pressure valve installations.
Trim – The internal parts of a valve that contact the media, such as the seat, disc, and stem.
Triple Offset – Design used in butterfly valves to reduce seat wear by offsetting the disc centerline from the body centerline in 2 directions and including a third offset on a metal-to-metal seat.
Trunnion – A mounted support mechanism used in ball valves to hold the ball in place.
Union Bonnet – A bonnet that is screwed onto the valve body for ease of disassembly.
V-Packing - V-shaped rings used in sets for sealing valve stems or pistons.
Valve – A mechanism used to control the flow of media.
Valve Envelope – The physical space or volume a valve occupies when installed.
Vault – An enclosure used to house and protect a valve or pipe system. Typically, a buried concrete structure.
Vent Plug – A small fitting used to vent trapped air or gas.
Vented Ball – A ball with a hole to relieve trapped pressure in the cavity of a closed valve.
Water Hammer – A pressure surge caused when fluid in motion is forced to stop or change direction suddenly.
Wetted Parts – The components of a valve that come into direct contact with the media being controlled.
WOG – Water, Oil, Gas; pressure rating indicating maximum allowable pressure for these media.
