P&ID Symbols and PFD Equipment Chart

Vessels and columns

• Vertical tankT-, V-
  Store liquid on a PFD or P&ID. Use for feed, product, or surge when the vessel stands upright.
• Horizontal vesselV-, D-
  A drum on its side. Common for surge, knock-out, or a reflux accumulator.
• Agitated reactorR-
  A stirred tank where mixing or reaction happens. The motor and impeller mark agitation.
• Trayed distillation columnC-, T-
  A tall tower with trays. Use on a PFD or P&ID when the column is trayed, not packed.
• Packed columnC-, T-
  A tower filled with packing instead of trays. Absorption, stripping, or packed distillation.
• Separator / knock-out drumV-, D-, KO-
  Knock liquid out of a vapor stream. Gas leaves the top; liquid leaves the bottom.
• Silo / hopperS-
  Store or feed solids. The cone marks a hopper bottom that discharges by gravity.
• Open tank / basinT-
  An open-top tank or basin. Wastewater, cooling-water sumps, and ponds use this form.

Pumps and compressors

• Centrifugal pumpP-
  The usual rotating pump on a PFD or P&ID. Liquid enters the eye and leaves at the discharge.
• Reciprocating pumpP-
  A piston or plunger pump for high pressure or metering. The square inside the circle marks the piston.
• Diaphragm pumpP-
  A sealed pump that moves fluid with a flexing diaphragm. Use for slurries or corrosives.
• Screw pumpP-
  A positive-displacement pump with helical rotors. Viscous oils and polymers often use it.
• CompressorK-
  Raise gas pressure. Draw this instead of a pump when the stream is vapor. Some sites use C- for compressors.
• Blower / fanB-
  Move air or flue gas at low pressure. Cooling-tower fans and aeration blowers use this mark.

Heat transfer

• Shell-and-tube exchangerE-
  The default process exchanger. One stream is in the shell; the other is in the tubes.
• Plate exchangerE-
  A compact exchanger made of stacked plates. Common on clean liquids and HVAC loops.
• Air coolerE-
  Reject heat to air with a finned bundle and a fan. Fin-fans on gas plants use this symbol.
• CondenserE-
  Turn vapor into liquid. Overhead condensers on columns and refrigeration units use it.
• ReboilerE-
  Add heat at the column base. This kettle form has a drum and a tube bundle; a thermosiphon reboiler is usually drawn as an exchanger.

Separation and solids

• FilterF-
  A vessel that holds a filter element. Cartridge and bag housings are often drawn this way; plate-and-frame filters look different.
• Disc-stack centrifugeCE-
  Separate liquid phases or fine solids with a stack of conical discs. Dairy and biotech use it.
• Decanter centrifugeCE-
  A horizontal bowl with a scroll that pushes solids out. Sludges and crystals use it.
• Cyclone
  Spin solids or droplets out of a gas. Dust collection and catalyst fines use this cone.
• Membrane module
  A membrane housing for RO, UF, or gas separation. Feed enters; permeate and retentate leave separately.
• Thin-film evaporatorE-
  A wiped-film evaporator for heat-sensitive or viscous feeds. The shaft marks the rotor.
• Rotary drum dryer
  A rotary drum dryer for wet solids. Spray dryers are drawn as a chamber with a nozzle, not this drum.

Valves

• Gate valveHV-, V-
  A block valve meant to be fully open or shut. Isolation on process lines uses this bow-tie.
• Globe valveHV-, V-
  Throttle a flow. The filled seat mark separates it from a gate valve.
• Ball valveHV-, V-
  Quarter-turn isolation with a ball. The hollow circle in the body is the ball.
• Butterfly valveHV-, V-
  A disc that turns in the line. Large pipes and dampers often use this mark.
• Check valve
  Allow flow in one direction only. Common on pump discharge lines to stop reverse flow.
• Control valveFV-, TV-, LV-, PV-
  A throttling valve with an actuator. Pair it with a controller bubble on a P&ID.
• Pressure relief / safety valvePSV-, PRV-
  Protect a vessel or line from overpressure. The outlet points up or to a flare header.
• Three-way valveXV-, TV-
  Split or mix three ports. Diverting and mixing services use this T-body.
• Needle valveHV-, V-
  Fine manual throttle on sample, vent, or instrument lines. The small triangle on the stem marks the needle plug.
• Diaphragm valveHV-, V-
  A weir valve sealed by a diaphragm. Clean, slurry, and corrosive services use it.

Instruments

• Field-mounted bubble
  A discrete instrument in the field. ISA 5.1 draws this as a plain circle.
• Panel-mounted bubble
  An instrument in the primary panel or console. The horizontal bar marks that location.
• DCS / shared-display bubble
  A shared display or control function in a DCS. ISA 5.1 puts the circle in a square.
• PLC bubble
  A function in a programmable controller. ISA 5.1 draws a diamond inside a square.
• Flow transmitter (FT)FT
  Measure flow and send a signal. Place it on the line, often next to an orifice or meter.
• Level transmitter (LT)LT
  Measure liquid level in a vessel. Two side taps on the tank go to the LT bubble.
• Pressure transmitter (PT)PT
  Measure pressure and transmit it. Tap the line or vessel and run a signal to a PIC or alarm.
• Temperature transmitter (TT)TT
  Measure temperature, usually through a thermowell. The well is the short stub on the line.
• Orifice plateFE, FT
  A restriction that creates a flow signal. Pair the flanges with an FT or FI bubble.

Lines and connectors

• Process line
  A solid line carrying process fluid. Arrowheads show direction on a PFD or P&ID.
• Electrical signal
  An electrical instrument signal (4–20 mA etc.). ISA 5.1 draws this as a dashed line.
• Pneumatic signal
  An air signal to a valve positioner or transmitter. Solid line with paired slashes, not a dash.
• Data link / software signal
  A software or internal data link. ISA 5.1 marks this with small circles on the line.
• Off-page connector
  Continue a line on another sheet. The letter matches the connector on the destination page.
• Stream number diamond
  Number a material stream on a PFD so it can be looked up in the stream table.

Special

Not part of ISA/ISO; our convention for algae and bioprocess drawings.

• Photobioreactor (tubular)
  A closed algal or photosynthetic reactor made of glass or plastic tubes, not a stirred tank.
• Raceway pond
  An open oval pond with a paddle wheel. Algae farms and some wastewater plants use this layout.