Valves & Fittings

Start here: ten words every newcomer needs

Overheard on the job

Real-sounding lines from the floor, translated into plain English.

• Block valve's passing, the bleeder won't go dead, so we're spading the flange before anybody breaks it.

  TranslationThe isolation valve leaks through its seat, as shown by the vent between valves still discharging, so a solid blind plate will be installed for positive isolation before the joint is opened.

• Gland's bottomed out and it's still weeping, put it on the outage list for a repack.

  TranslationThe packing gland has no adjustment left and the stem still leaks slightly, so the valve needs new packing at the next shutdown.

• Control valve's hunting at 8 percent open, it's oversized, we need reduced trim with equal percentage.

  TranslationThe control valve keeps cycling while nearly closed because its capacity is too large; smaller internals with an exponential characteristic would control better.

• Two-hole that flange and cut a dutchman in, the spool's an inch and a half short.

  TranslationOrient the flange so bolt holes straddle the centerline and weld in a short filler piece of pipe, because the fabricated section is too short.

• Fail-closed fuel gas valve won't stroke, the handjack's still wound in from the turnaround.

  TranslationThe fuel gas valve, which shuts on loss of air, cannot move through its travel because its manual override was left engaged after maintenance.

• Discharge check slams on every pump trip, the whole rack jumps, spec a nozzle check.

  TranslationThe pump discharge check valve closes violently after flow reverses, causing a pressure surge, so a fast-closing non-slam check valve should replace it.

• Golden weld's shot and clean, pull the gags off the safeties and we can line it up.

  TranslationThe final untested tie-in weld passed radiography, so the test clamps can come off the safety valves and the system can be put in service.

The families of valves, from gate and globe to triple-offset butterfly and safety valves, and what each is built to do.

• Ball valvealso quarter-turn ball
  A quarter-turn valve that opens and closes by rotating a ball with a bore through it.
• BFValso butterfly
  Butterfly valve: the clipped form used on valve tags, takeoff sheets and HVAC and fire protection drawings. Shop talk
• Butterfly valvealso BFV, butterfly
  A quarter-turn valve with a disc on a shaft that rotates in the bore to open, close or throttle flow.
• Check valvealso non-return valve, NRV
  A self-acting valve that lets fluid pass in one direction and closes on its own when flow tries to reverse.
• Control valvealso CV, modulating valve
  A power-operated valve that modulates flow on a controller signal to hold pressure, level, flow or temperature at setpoint.
• Diaphragm valvealso weir valve
  A valve that closes by pressing a flexible diaphragm down onto a weir or the body floor, with no stem packing.
• Floating ball valvealso floating ball
  A ball valve whose ball is held only by the seats and is pushed downstream by line pressure to make the seal.
• Gate valvealso sluice valve
  A multi-turn isolation valve that lifts a flat or wedge-shaped gate clear of the flow path to open.
• Globe valvealso stop valve, screw-down stop valve
  A linear-motion valve that throttles well because its disc moves straight onto a seat across an S-shaped flow path.
• Knife gate valvealso knife gate
  A gate valve with a thin, sharp-edged blade that cuts through slurry, pulp or solids as it closes.
• Needle valvealso needle
  A small valve with a long tapered stem tip that meters tiny flows with fine adjustment.
• Pinch valve
  A valve that shuts off flow by squeezing a flexible rubber sleeve closed, either mechanically or with air pressure.
• Plug valvealso plug cock
  A quarter-turn valve that rotates a tapered or cylindrical plug with a port through it to start or stop flow.
• Relief valvealso PRV, liquid relief valve
  A spring-loaded valve for liquid service that opens gradually as pressure rises past its set point.
• Safety valvealso PSV, pop valve
  A spring-loaded pressure relief valve for steam, gas or vapor that opens with a rapid full lift at set pressure.
• Solenoid valvealso solenoid, SOV
  An electrically operated valve in which a coil pulls a plunger to open or close an orifice.
• Triple-offset butterfly valvealso TOV, triple offset
  A metal-seated butterfly valve whose geometry lets the seal touch the seat only at the end of closure, for tight, rub-free shutoff.
• Trunnion-mounted ball valvealso trunnion ball valve, trunnion
  A ball valve whose ball is anchored top and bottom on trunnions while spring-loaded seats press against it.

The body, bonnet, stem, packing, seats and other components inside and on top of a valve.

• Backseatalso back seat, backseating
  A seat on the underside of the bonnet that a stem shoulder seals against at full open, isolating the packing.
• Bodyalso valve body, shell
  The main pressure-containing shell of a valve, carrying the flow passage and the end connections.
• Bonnetalso cover
  The cover that closes the top of a valve body and carries the stem, packing and often the yoke.
• Cagealso sleeve
  A slotted or drilled sleeve around a control valve plug that guides it and shapes how flow changes with travel.
• Discalso disk, plug
  The movable closure element that seats to stop flow in globe, check, safety and butterfly valves.
• Glandalso gland follower, packing gland
  The part that presses down on the packing to load it against the stem, adjusted by the gland nuts.
• OS&Yalso OS and Y, outside screw and yoke
  Outside screw and yoke: a rising-stem valve design with its stem threads above the packing, out of the fluid.
• Packingalso stem packing, stuffing box packing
  Compressible rings packed around a valve stem to stop process fluid leaking out to atmosphere.
• Seatalso seat ring, valve seat
  The surface inside a valve that the closure member presses against to stop flow.
• Stemalso spindle, shaft
  The rod that carries motion from the handwheel, lever or actuator through the bonnet to the closure member.
• Trimalso internals, valve trim
  The replaceable internal parts of a valve that touch the process fluid, such as seat, disc or plug, stem and cage.
• Wedgealso gate, disc
  The tapered closure member of a gate valve that is driven down between two inclined seats to seal.
• Yokealso bonnet yoke, yoke arm
  The frame on top of a valve bonnet that holds the stem nut or mounts the actuator above the packing.

How valves pass and regulate flow: flow coefficients, characteristics, cavitation, shutoff classes and the talk of throttling.

• Bubble-tightalso zero leakage, drop-tight
  Shut off with no visible seat leakage when tested with air or gas under water. Shop talk
• Cavitationalso cavitating
  Vapor bubbles forming and then collapsing in a liquid passing through a valve, causing noise, vibration and pitting.
• Crackalso crack open, cracked
  To open a valve just slightly, letting a small, controlled flow through. Shop talk
• Cvalso flow coefficient, valve coefficient
  Flow coefficient: US gallons per minute of 60 degree F water a valve passes with a 1 psi pressure drop.
• Equal percentagealso equal %, =%
  Describes a valve characteristic where each equal step of travel changes flow by the same percentage of current flow.
• Flashingalso flash
  Liquid partly turning to vapor through a valve because downstream pressure stays below its vapor pressure.
• Flow characteristicalso valve characteristic, trim characteristic
  The relationship between how far a valve is open and how much flow it passes.
• Huntingalso cycling, oscillating
  A control valve or loop swinging back and forth around setpoint instead of settling. Shop talk
• Passingalso letting by, leaking by
  Leaking through the seat while closed, so fluid still gets past a valve that is supposed to be shut. Shop talk
• Pinch backalso pinch in, pinch it down
  To close a valve partway to cut flow or pressure, without shutting it. Shop talk
• Rangeabilityalso turndown
  The ratio of the largest to the smallest flow a control valve can regulate while keeping its characteristic.
• Shutoff classalso leakage class, seat leakage class
  A rating of how much seat leakage a closed control valve is allowed, from Class I to Class VI.
• Stictionalso stick-slip, sticky valve
  Static friction that makes a control valve stick, then jump, instead of moving smoothly with its signal. Shop talk
• Throttlealso throttling, modulate
  To hold a valve partly open on purpose to restrict and regulate flow or pressure.

Actuators, positioners, fail positions and the testing and troubles of powered valves.

• Actuatoralso operator, valve operator
  The powered device that opens, closes or positions a valve using air, hydraulic oil or an electric motor.
• Bench setalso spring range, bench range
  The air pressure range over which a spring-and-diaphragm actuator strokes the valve with no process pressure acting.
• Double-actingalso DA
  Describes an actuator that uses air or oil pressure to drive in both directions, with no return spring.
• Fail-closedalso FC, air-to-open
  Describes a valve that springs shut when it loses air, power or its control signal.
• Fail-openalso FO, air-to-close
  Describes a valve whose actuator drives it fully open when air, power or signal is lost.
• Handjackalso handwheel override, manual override
  The manual handwheel override fitted to a pneumatic actuator so a valve can be positioned by hand. Shop talk
• MOValso motor operator, motorized valve
  Motor-operated valve: a valve driven by an electric actuator with a motor, gearbox, torque switch and limit switches.
• Partial stroke testalso PST, partial stroke
  Moving an emergency shutdown valve a small part of its travel while online, to prove it is not stuck.
• Positioneralso valve positioner, digital valve controller
  A device on a control valve that compares the control signal with actual valve position and adjusts air to match.
• Scotch yokealso scotch yoke actuator, SY actuator
  A rotary actuator mechanism that turns the straight push of a piston into a 90 degree shaft rotation through a slotted yoke.
• Spring-returnalso single-acting, spring-to-close
  Describes a single-acting actuator that uses air to move one way and a spring to move back and fail safe.
• Strokealso stroke test, full stroke
  To run an automated valve through its full travel to prove it moves, seats and reports position correctly.
• Torque outalso torqued out, torque trip
  For a motor-operated valve to stop on its torque switch because it met more resistance than expected. Shop talk

Pressure classes, flange faces, weld and thread ends, gaskets and the craft of making up joints.

• Butt weldalso BW, buttweld
  An end connection where a beveled valve or fitting end is welded straight to beveled pipe with full penetration.
• Hot boltingalso hot bolt, hot bolt replacement
  Replacing or retorquing flange bolts one at a time while the line stays in service. Shop talk
• Make upalso makeup, made up
  To screw a threaded joint together and tighten it, or to assemble and torque a flanged joint. Shop talk
• NPTalso MPT, FPT
  National Pipe Taper: the tapered pipe thread used for threaded valves and fittings in North America.
• Pipe dopealso dope, thread sealant
  Paste thread sealant brushed on male pipe threads before makeup to seal and lubricate the joint. Shop talk
• PNalso nominal pressure, PN rating
  Pressure nominal: the metric rating series, such as PN 16 or PN 40, used for European and ISO valves and flanges.
• Pressure classalso class, pound rating
  The standardized rating step, such as 150, 300 or 600, that sets a valve or flange's allowable pressure at each temperature.
• Raised facealso RF, RF flange
  A flange facing where the gasket surface stands slightly proud of the bolt circle area, concentrating gasket load.
• RTJalso ring joint, R-ring
  Ring type joint: a flange face with a machined groove that holds a solid metal ring gasket for high pressure.
• Socket weldalso SW, socket weld end
  An end connection where the pipe slides into a recessed socket and is joined by a fillet weld around the outside.
• Spiral wound gasketalso spiral wound, SWG
  A flange gasket made of a V-shaped metal strip wound with a soft filler, held between an outer ring and usually an inner ring.
• Two-holingalso two-hole, straddle the centerline
  Orienting a flange so two bolt holes straddle the top centerline instead of one hole sitting dead on top. Shop talk
• Waferalso wafer body, wafer style
  A thin valve body clamped between two pipe flanges by long bolts passing outside it.
• WOGalso CWP, cold working pressure
  Water, oil, gas: a cold working pressure rating stamped on small threaded valves, such as 600 WOG.

Elbows, tees, reducers, nipples, blinds and the pipefitter vocabulary of building and tying in piping.

• Bull plugalso bullplug, tapped bull plug
  A solid or tapped round-nosed male plug used to close the end of a swage, fitting or valve outlet.
• Close nipplealso all-thread nipple, running nipple
  The shortest threaded nipple made, threaded along its whole length with no plain section in the middle. Shop talk
• Dutchmanalso filler piece, pup
  A short filler piece of pipe cut in to close a gap or correct a misfit between two spools. Shop talk
• Elbowalso ell, 90
  A fitting that changes the direction of a pipe run, usually by 90 or 45 degrees.
• Fishmouthalso fish mouth, saddle cut
  A saddle-shaped cut on the end of a branch pipe so it sits flush against the curve of a larger pipe. Shop talk
• Golden weldalso golden joint, closure weld
  The final tie-in weld between new and existing piping that cannot be included in the hydrotest. Shop talk
• Hot tapalso hot tapping, pressure tapping
  A new branch connection made on a pipe or vessel while it stays in service, cutting through a valve.
• Nipplealso pipe nipple, TBE nipple
  A short length of pipe, threaded or plain on its ends, used to connect two fittings or a valve to a fitting.
• Oletalso weldolet, sockolet
  A forged branch fitting welded onto a run pipe to make an outlet without cutting in a tee.
• Reduceralso increaser
  A fitting that joins a larger pipe to a smaller one, either on a common centerline or with one side flat.
• Spadealso paddle blind, skillet
  A solid blank plate with a handle, slipped between flanges to positively isolate a line. Shop talk
• Spectacle blindalso figure 8 blind, spec blind
  A figure-8 shaped plate between two flanges with one solid end for isolation and one open ring for flow.
• Street ellalso street elbow, street 90
  A threaded or sweat elbow with one male and one female end, so it screws straight into another fitting. Shop talk
• Swagealso swedge, swage nipple
  A forged reducing nipple that steps a small bore line down one or more sizes, with threaded, plain or beveled ends.
• Teealso T
  A T-shaped fitting that splits or joins flow, with a straight run and a side branch.
• Unionalso ground joint union
  A three-piece threaded fitting that lets a section of pipe or a valve be disconnected without turning the pipe.

Leak standards, pressure tests, isolation practice, relief valve behaviour and the ways valves fail.

• Bleederalso bleed valve, vent valve
  A small vent or drain valve used to release pressure or fluid, especially between two block valves. Shop talk
• Car sealalso carseal
  A numbered tamper seal fixed to a valve handle so it cannot be moved without visibly breaking the seal.
• Chatteralso chattering
  Rapid, violent opening and closing of a relief or check valve that hammers the disc against the seat.
• Cheater baralso cheater, snipe
  A length of pipe slipped over a wrench or valve handle to gain extra leverage on something stuck. Shop talk
• Cracking pressurealso crack pressure, opening pressure
  The pressure at which a check valve or relief valve first starts to open and pass a trickle of flow.
• Double block and bleedalso DBB
  Isolation using two closed seats in series with a vent or drain between them to prove the isolation holds.
• F-wrenchalso valve wrench, wheel key
  An F-shaped steel bar that hooks over handwheel spokes to give extra turning leverage on a valve. Shop talk
• Fire-safealso fire-tested, fire safe
  Describes a valve built to limit leakage through and around it during and after an external fire.
• Fugitive emissionsalso FE, fugitives
  Small unintended leaks of process gas or vapor to atmosphere, mostly from valve stem seals and joints.
• Gagalso test gag, gagged
  A clamp or screw fitted to a safety valve to hold its disc shut during a system pressure test.
• Gallingalso galled, galled up
  Severe adhesive wear where loaded metal surfaces slide, cold-weld together and tear material out.
• Hydroalso hydrostatic test, hydrotest
  A hydrostatic pressure test: filling a valve, piping system or vessel with water and pressurizing it to prove strength. Shop talk
• Popalso lift, blow
  For a safety valve to lift suddenly and fully open, discharging with a loud blast at set pressure. Shop talk
• Pressure lockingalso pressure lock
  A closed gate valve that cannot be opened because trapped pressure in its bonnet cavity jams the wedge into both seats.
• Repackalso repacking, pack it
  To pull the old packing out of a valve stuffing box and install a new set of rings. Shop talk
• Shell testalso body test, hydrostatic shell test
  A hydrostatic pressure test of the valve body and bonnet, run with the valve partly open, to prove the shell holds.
• Simmeralso simmering
  For a safety valve to leak with an audible hiss or seep just below its set pressure, before it pops.
• Slamalso check valve slam, slamming
  A check valve banging shut after flow has already reversed, sending a pressure surge through the line. Shop talk
• Water hammeralso hydraulic shock, surge
  A pressure surge, heard as a bang, when moving liquid is stopped or reversed suddenly.
• Weepingalso weeper, weep
  Leaking a drop or wisp at a time from packing, a gasket, a threaded joint or a casting. Shop talk
• Wire drawingalso wiredrawing, steam cutting
  Erosion of thin grooves across a valve seat by a high-velocity jet leaking through a tiny gap.

Frequently asked questions

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