P&ID Symbols

Gate valve

Two opposed triangles with a vertical bar through the centre for an on/off isolating valve whose gate slides across the flow. Use it for block valves that stay fully open or fully closed.

IND_PID_SYMBOLS_GATE_VALVE

Globe valve

Valve body with a solid dot at the centre, marking a globe-pattern seat. Typical for throttling duties and bypasses where flow is adjusted by hand.

IND_PID_SYMBOLS_GLOBE_VALVE

Ball valve

Valve body with an open circle at the centre for a quarter-turn valve with a bored ball. Common on utility lines and tight shut-off services.

IND_PID_SYMBOLS_BALL_VALVE

Butterfly valve

Valve body with a vertical bar and a centre dot representing the disc on its spindle. Used on large-bore lines for isolation or coarse throttling.

IND_PID_SYMBOLS_BUTTERFLY_VALVE

Check valve

Valve body with a solid dot on the inlet corner, the general non-return valve. Draw it with the inlet on the left so the permitted flow runs left to right.

IND_PID_SYMBOLS_CHECK_VALVE

Plug valve

Valve body with a solid rectangle at the centre standing for the rotating plug. Used for quarter-turn isolation on slurries, gas and viscous fluids.

IND_PID_SYMBOLS_PLUG_VALVE

Needle valve

Valve body with a small solid wedge pointing into the seat, for fine flow adjustment on instrument connections, sampling points and small bleed lines.

IND_PID_SYMBOLS_NEEDLE_VALVE

Diaphragm valve

Valve body with an arc over the centre representing the flexible diaphragm that closes onto a weir. Chosen for corrosive, abrasive or hygienic services.

IND_PID_SYMBOLS_DIAPHRAGM_VALVE

Angle valve

Two triangles at right angles: the flow enters from the left and leaves downward, or the reverse. Use it where the valve also turns the line through 90 degrees.

IND_PID_SYMBOLS_ANGLE_VALVE

Three-way valve

In-line valve body with a third port pointing down, for diverting one stream into two or mixing two streams into one.

IND_PID_SYMBOLS_THREE_WAY_VALVE

Safety relief valve

Angle valve with a spring above it: the inlet comes from the protected equipment below and the discharge leaves to the side. Marks a pressure relief device set to open on overpressure.

IND_PID_SYMBOLS_SAFETY_RELIEF_VALVE

Control valve, diaphragm actuator

Valve body with a stem and a domed spring-and-diaphragm actuator on top. The standard way to show an air-operated modulating control valve in a control loop.

IND_PID_SYMBOLS_CONTROL_VALVE_PNEUMATIC

Control valve, electric motor actuator

Valve body with a stem and a circle marked M for an electric motor actuator. Used for motor-operated valves, whether on/off or modulating.

IND_PID_SYMBOLS_CONTROL_VALVE_MOTOR

Solenoid valve

Valve body with a stem and a rectangle crossed by a diagonal, the electromagnetic actuator. Shows an electrically switched on/off valve, often on pilot air or small process lines.

IND_PID_SYMBOLS_SOLENOID_VALVE

Hand-operated valve

Valve body with a stem ending in a T-bar for a handwheel. Use it where the drawing needs to state explicitly that the valve is operated by hand.

IND_PID_SYMBOLS_MANUAL_VALVE_HANDWHEEL

Centrifugal pump

Circle with two lines converging on the discharge side and a horizontal diameter, the centrifugal variant of the liquid pump. Rotate the block so the converging point faces the discharge.

IND_PID_SYMBOLS_CENTRIFUGAL_PUMP

Positive displacement pump (reciprocating)

Liquid pump outline with a piston and rod drawn inside, the reciprocating positive displacement form. Suitable for metering, dosing and high-pressure duties.

IND_PID_SYMBOLS_POSITIVE_DISPLACEMENT_PUMP

Compressor

Circle with two chords that narrow towards the outlet, the general symbol for a gas compressor or vacuum pump. The narrow end faces the high-pressure side.

IND_PID_SYMBOLS_COMPRESSOR

Fan or blower

Compressor-style circle with a three-blade impeller inside, for fans and blowers moving gas at low pressure rise such as ventilation, combustion air or drying air.

IND_PID_SYMBOLS_FAN_BLOWER

Vertical vessel

Upright cylindrical vessel with dished heads at both ends. Use it for drums, receivers, separators and reactors standing on end.

IND_PID_SYMBOLS_VERTICAL_VESSEL

Horizontal vessel

Cylindrical vessel lying on its side with dished heads, for accumulators, storage drums and horizontal separators.

IND_PID_SYMBOLS_HORIZONTAL_VESSEL

Atmospheric storage tank

Flat-bottomed tank with a low conical roof, the usual picture of a storage tank working at or near atmospheric pressure.

IND_PID_SYMBOLS_ATMOSPHERIC_TANK

Tray column

Tall vessel with dished heads and horizontal lines for trays, used for distillation, absorption and stripping columns. Remove or add tray lines to match the drawing scale.

IND_PID_SYMBOLS_COLUMN

Shell and tube heat exchanger

Long rectangle with a tube sheet near each end and a bundle of straight tubes between them. Represents a fixed tube-sheet exchanger; connect the shell-side and tube-side lines to the matching faces.

IND_PID_SYMBOLS_SHELL_TUBE_HEAT_EXCHANGER

Plate heat exchanger

Rectangle with three cross bars and a full diagonal cross, for gasketed or brazed plate exchangers that pass two fluids through alternate channels.

IND_PID_SYMBOLS_PLATE_HEAT_EXCHANGER

Liquid filter

Upright housing with a dashed line across it for the filter element. Use it for in-line liquid filters and cartridge housings when the filter type need not be detailed.

IND_PID_SYMBOLS_FILTER

Agitator

Vertical shaft ending in an angled blade, the general stirrer symbol. Insert it at the top of a vessel so the shaft enters through the head; the base point is the top of the shaft.

IND_PID_SYMBOLS_AGITATOR

Field-mounted instrument

Plain circle for a discrete instrument mounted in the field, close to the process. Fill in the FUNCTION attribute with the identification letters and LOOP with the loop number.

IND_PID_SYMBOLS_INSTRUMENT_FIELD

Panel-mounted instrument

Circle with a solid horizontal line, for a discrete instrument in a primary location such as the control room panel, normally accessible to the operator.

IND_PID_SYMBOLS_INSTRUMENT_PANEL

Instrument behind the panel

Circle with a dashed horizontal line, for a discrete instrument in a primary location that is not normally accessible to the operator, such as inside a cabinet or behind the panel.

IND_PID_SYMBOLS_INSTRUMENT_BEHIND_PANEL

Shared display or control (DCS)

Circle inside a square with a solid horizontal line, for a function shown or controlled on a shared display, typically a DCS operator station in the control room.

IND_PID_SYMBOLS_INSTRUMENT_DCS

PLC function

Diamond inside a square with a solid horizontal line, for a function performed by a programmable logic controller and accessible to the operator.

IND_PID_SYMBOLS_INSTRUMENT_PLC

Process line

Heavy solid line for main process piping. Draw it on the process line layer so it stays thicker than signal and utility lines.

IND_PID_SYMBOLS_LINE_PROCESS

Pneumatic signal line

Thin solid line with pairs of short slashes, for an instrument air signal between a transmitter, controller and actuator.

IND_PID_SYMBOLS_LINE_PNEUMATIC_SIGNAL

Electrical signal line

Dashed line for an electrical or electronic signal, such as a 4-20 mA loop between a field transmitter and the control system.

IND_PID_SYMBOLS_LINE_ELECTRICAL_SIGNAL

Capillary tube

Thin line with small crosses, for a filled capillary system linking a sensing bulb or remote seal to its instrument.

IND_PID_SYMBOLS_LINE_CAPILLARY

Data link

Thin line interrupted by small circles, for a communication or software link between systems, such as a fieldbus or a link between a PLC and the DCS.

IND_PID_SYMBOLS_LINE_DATA_LINK

Reducer

Triangle on the line marking a change of pipe size, with the wide side towards the larger bore. Flip the block to match the direction of reduction.

IND_PID_SYMBOLS_REDUCER

Flanged connection

Two short parallel bars across the line for a bolted flange joint. Use it where a joint must be shown, for example at equipment nozzles or removable spools.

IND_PID_SYMBOLS_FLANGE_PAIR

Spectacle blind

Solid disc on the line with an open ring beside it, a spectacle blind drawn in the closed position. Swap the disc and ring to show it open.

IND_PID_SYMBOLS_SPECTACLE_BLIND