P&ID Symbols List: Valve, Piping & Instrument Symbols (Free PDF)

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What Are P&ID Symbols?

P&ID symbols are standardized graphical notations used on Piping and Instrumentation Diagrams (P&IDs) per ISA, ISO, and ANSI standards. These drawing symbols represent every component in a process system (valves, instruments, piping elements, and equipment) allowing engineers to read and design P&ID diagrams regardless of language or company. The ISA S5.1 standard is the most widely referenced for instrumentation symbols, where the first letter identifies the measured variable (T=temperature, P=pressure, F=flow, L=level). P&IDs develop through three stages: BFD to PFD to P&ID.

P&ID symbols are used in oil & gas, chemical, pharmaceutical, power generation, water treatment, and HVAC piping systems. While the core symbol library is the same across industries, HVAC P&ID symbols may include additional notation for dampers, air handling units, and ductwork per ASHRAE standards.

More about P&ID symbols, standards, and best practices

Main symbol categories:

Category	What They Show
Piping	Flow direction, pipe size, material, line number
Valves	Gate, globe, check, ball, butterfly, control valves
Fittings	Elbows, tees, reducers, flanges
Instruments	Transmitters, controllers, switches, gauges
Equipment	Pumps, compressors, heat exchangers, vessels
Signal Lines	Pneumatic, electrical, digital, hydraulic

ISA S5.1 first-letter convention: The first letter always identifies the measured variable (T=temperature, P=pressure, F=flow, L=level). So when you see “TIC-101,” you instantly know it’s a Temperature Indicating Controller. This makes reading any P&ID faster and helps you catch errors in tag assignments.

P&ID vs. Piping Isometric:

Document	Purpose	Shows
P&ID	Process logic, control philosophy	Schematic relationships, all instruments/valves
Piping Isometric	Fabrication and construction	Physical dimensions, routing, weld locations

A P&ID tells you what connects to what and how it’s controlled. An isometric tells you how to build it. Both reference the same line numbers and components, but serve different audiences.

Common mistake: Using outdated P&ID revisions for construction or commissioning. P&IDs evolve throughout project phases - the “Issued for Construction” (IFC) version may differ significantly from the earlier “Issued for Design” version. Always verify you’re working from the latest issued revision, and mark up as-built changes during construction for the final “As-Built” P&ID.

Field tip: When walking down a system against the P&ID, bring colored markers. Mark installed items green, missing items red, and discrepancies yellow. By the time you finish, you have a visual punch list. Also check that valve tag numbers in the field match the P&ID - mismatched tags cause operators to open the wrong valve.

Piping P&ID Symbols

Pipe symbols for P&ID drawings represent flanges, caps, reducers, blinds, spectacle blinds, orifice plates, and other piping components. These are the most commonly used piping symbols in process engineering diagrams.

Flange General	Flange Blind	Reducer Flange
Welded Cap	Threaded Cap	Reducer
Union	Open Spectacle Blind	Closed Spectacle Blind
Open Spacer	Closed Spacer	Orifice Union
Orifice Plate	Spring	Sight Flow Glass
Plug	Piston Operator	Open Drain
Manual Handwheel	Hose Connection	Expansion Flange
Diaphragm	Closed Drain	Bursting Disc
Blind	Sample Connection Point

Valve Symbols for P&ID

The valve symbol in a P&ID drawing indicates the type and function of each valve in the piping system. Valve P&ID symbols are among the most important to learn, as valves appear on every process diagram. Below are the most common valve symbols per ISA S5.1: gate valve, globe valve, ball valve, check valve, butterfly valve, control valve, safety relief valve, plug valve, needle valve, and solenoid valve symbols.

Gate Valve Symbol	Globe Valve Symbol	Ball Valve Symbol
Butterfly Valve Symbol	Plug Valve Symbol	Needle Valve Symbol
Diaphragm Valve	Valve with Orifice	Slide Gate Valve
Knife Valve	Conduit Gate Valve	Pinch Valve
Block and Bleed	Double Block and Bleed	Self Draining Valve
Float Valve	Y Globe Valve	Y Blowdown Valve
Check Valve Symbol	Angle Valve	Angle Globe Valve
Angle Blowdown	Pressure Vacuum Valve	Vacuum Breaker
Pressure Relief Valve Symbol	Angle Check Valve	Valve (Generic)
3-Way Gate Valve	3-Way Globe Valve	3-Way Ball Valve
3-Way Plug Valve	3-Way Valve Normal	4-Way Valve
4-Way Plug Valve	Control Valve	Control Valve Internal
Control Valve Symbol (External)	Motor Activated Valve	Electro Hydraulic
3-Way Control Valve	Thermal Release	Hydraulic Valve
4-Way Solenoid	Solenoid Manual Reset

Strainers P&ID Symbols

Y Strainer	Basket Strainer	Cone Strainer
Duplex Strainer	Filter	Flat Plate Strainer
Sump Strainer	T Strainer

Lines P&ID Symbols

Process Lines	Instrumentation Lines	Equipment Outline
Hydraulic Signal	Electrical Supply	Pneumatic Signal (N2)
Pneumatic Signal (Air)	Control Panel / Enclosure	Capillary Tubing (Filled)
Electrical Signal	Redundant	Slope
System Link (Digital/Software)	Undefined Signal	Ultrasonic Signal

Other mechanical/electrical/digital lines P&ID symbols:

Process and Plant Equipment

General Plant Equipment P&ID Symbols

Agitator / Mixer	Air Blown Cooler	Alkylation
Automatic Stoker	Axial Compressor	Boom Loader
Briquetting Machine	Centrifugal Blower	Centrifugal Compressor 2
Centrifugal Compressor 3	Centrifugal Compressor	Chimney Tower
Combustion Chamber	Condenser	Conveyor
Cooler	Cooling 2	Cooling Tower
Counterflow Forced Draft	Counterflow Natural Draft	Crossflow Inducted
Diesel Motor	Double Flow Turbine	Drum
Dryer	Electric Motor	Electric Heater
Elevator 2	Elevator	Extractor Hood
Fin Fan	Fired Heater	Fluid Catalytic Cracking
Fluid Cooking	Fluidized Reactor	Furnace
Hoist	Hose Reel	Hydrocracking
Hydrodesulfurization	Induced Flow Air Cooler	Induced Draft Cooling Tower
Light Water Station	Liquid Ring Vacuum	Mixing Reactor
Motor	Oil Burner	Overhead Conveyor
Packer Tower	Plate Tower	Positive Displacement 2
Positive Displacement	Reciprocating Compressor	Reformer
Rotary Compressor 2	Rotary Compressor	Scraper Conveyor
Screw Conveyor	Silencer	Skip Hoist
Spray Cooler	Tank	Thin-Film Evaporator
Tubular	Turbine Driver	Vent
Vertical Turbine

Pumps P&ID Symbols

Cavity Pump	Centrifugal Pump 01	Centrifugal Pump 02
Centrifugal Pump 03	Centrifugal Pump 04	Centrifugal Pump 05
Gear Pump	Horizontal Pump	ISO Centrifugal Pump
ISO Diaphragm Pump	ISO Gear Pump	ISO Liquid Pump
ISO Positive Displacement Pump	ISO Progressive Pump	ISO Screw Pump
Liquid Ring Vacuum Pump	Peristaltic Pump	Positive Displacement Pump 01
Positive Displacement Pump 02	Positive Displacement Pump 03	Proportionating Pump
Pump 01	Reciprocating Pump 01	Reciprocating Pump 02
Rotary Gear Pump	Rotary Pump	Screw Pump 01
Screw Pump 02	Submersible Pump	Sump Pump
Turbine Pump	Vacuum Pump	Vertical Pump 01
Vertical Pump 02

Compressors P&ID Symbols

AC Air Compressor	Air Compressor	Axial Compressor
Centrifugal Blower	Centrifugal Compressor 01	Centrifugal Compressor 02
Centrifugal Compressor 03	Centrifugal Compressor 04	Compressor 01
Compressor 02	Compressor Silencers	Compressor Vacuum Pump
Diaphragm Compressor	Ejector Compressor	Gas Blower
Liquid Ring Compressor	Piston Compressor	Reciprocating Compressor 01
Reciprocating Compressor 02	Reciprocating Compressor 03	Ring Compressor
Roller Vane Compressor	Rotary Compressor 01	Rotary Compressor 02
Rotary Compressors and Silencers	Screw Compressor	Selectable Compressor
Turbo Compressor

Heat Exchangers P&ID Symbols

TEMA Type BEM	Exchanger	Condenser 2
Air Cooled Exchanger	TEMA Type AEM	U-Tube Heat Exchanger 2
Single Pass Heat Exchanger	Heat Exchanger	Shell and Tube 2
Spiral Heat Exchanger	Single Pass HX 2	TEMA Type AEL
Shell and Tube 4	TEMA Type NEN	Spiral HX 2
Plate and Frame	Condenser	Straight Tubes HX
TEMA Type BKU	Shell and Tube 5	TEMA Type BEU
U-Tube Heat Exchanger	Shell and Tube	Reboiler Heat Exchanger
Hairpin Exchanger 2	Floating Head HX	Shell and Tube 3
Heater	Kettle Heat Exchanger	Shell and Tube 6
Single Pass Heat	Plate Heat Exchanger	Heat Exchanger 3
Evaporative Condenser	Boiler 2	Reboiler
Finned Tubes HX	Hairpin Exchanger	Plate Exchanger
Double Pipe HX	Double Pipe Heat	Boiler
Heat Exchanger 2	Air Cooled Exchanger 2	Cooling Tower
Coil Tubes HX

Vessels P&ID Symbols

Bag	Bag ISO	Barrel
Barrel ISO	Bin	Boiler
Brackets Vessel	Column	Cone Roof Tank
Covered Tank	Dished Ends Vessel	Dome Boiler
Dome Roof Tank	Double Wall Tank	Drum
Electrical Heating Vessel	Floating Roof Tank	Fluidized Bed Column
Gas Bottle	Heating Cooling Jacket Vessel	Hot Liquid Boiler
Internal Floating Roof Tank	Knockout Drum	Mixing Vessel
Onion Tank	Open Bulk Storage	Open Tank
Packed Tower	Packing Column 01	Packing Column 02
Pit Vessel	Plate Tower	Staggered Baffle Tray Column
Tank 01	Tank 02	Tank 03
Tank 04	Thermal Insulation Vessel	Tray Column
Vertical Vessel	Wastewater Treatment

Motors, Generators, and Turbines P&ID Symbols

AC Generator	AC Motor	DC Generator
DC Motor	Diesel Motor	Electric Motor
Gear	Generator	Motor 01
Motor 02	Motor Driven Turbine	Motor Generator
Step Motor	Turbine	Turbine Driver
Vertical Turbines

Filters P&ID Symbols

The filter symbol in P&ID drawings represents liquid or gas filtration equipment. Common filter P&ID symbols include cartridge filters, bag filters, sand filters, water filters, rotary drum filters, and spray nozzles. The standard filter symbol is a triangle with the apex pointing down (gravity flow) or up (pressure flow), while strainers use a different notation (see Strainers section above).

P&ID filter symbols: cartridge filter, bag filter, sand filter, water filter, plate filter, rotary drum filter, spray nozzle, and duplex filter.

ISA Instrument Symbols for P&ID

ISA P&ID symbols follow the ISA S5.1 standard (Instrumentation Society of Automation) for the identification of measurement and control instrumentation on Piping & Instrumentation Diagrams. The ISA symbology uses identification codes and graphic symbols to represent every instrument, controller, transmitter, and switch on the P&ID drawing.

The symbology of the instrument is placed in a circle of 7/16 “or 12 mm (see below), At the top there is the functional identification (of the instrument or device) composed with max 5 letters, and at the bottom, there is the identification of the loop (measurement and/or control) consists of a progressive number of 3 or 4 numbers, followed by a literal suffix to identifies two or more identical instruments inserted in the same chain and therefore having the same functional identification;

The circle that identifies the instrument or device has:

• Continue Line in the center: for an instrument suitable for control room mounting

• The dotted line in the center: for an instrument suitable for technical room mounting

• No line in the center: for an instrument suitable for field application

If an instrument has a circumscribed square means that it is an integrated instrument as a function in a DCS (Distributed Control System) or PLC (Programmable Logic Controller).

T - First Letter (Measured variable)	RC - Later letters (Functions)	101 - Loop number	A - Suffix
Functional identification	Functional identification	Loop identification	Loop identification

Graphical representation of a temperature recorder controller of the 101A loop, suitable for control room mounting The following tables show:

• Table 1 identifying the function of the instruments or devices
• Table 2 the graphic identification of the valves
• Table 3 the graphic identification of the actuators
• Table 4 identifies the safety conditions of the valves and actuators

At the end will also be reported the literal and graphic symbols of the power supplies and signals of the instrumentation.

Table 1 - Functions of Instruments

Letter	First Letter - Measured variable	First Letter - Modified	Following Letters - Passive function	Following Letters - Active function	Following Letters - Modifier
A	Analysis			Alarm
B	Burner or combustion
C	User (1) choice			Control
D	User (1) choice	Differential
E	Voltage		Element (primary)
F	Flow	Fraction
G	User (1) choice		Glass (2)
H	Hand				High (3)
I	Current		Indicate
J	Power	Scan
K	Time schedule	Time rate of change		Control station
L	Level		Light		Low (4)
M	User (1) choice	Momentary			Middle or intermediate
N	User (1) choice
O	User (1) choice		Orifice or restriction
P	Pressure or vacuum		Point test
Q	Quantity	Totalize or integrate
R	Radioactivity		Record
S	Speed or frequency	Safety		Switch
T	Temperature			Transmit
U	Multivariable		Multifunction	Multifunction	Multifunction
V	Vibration			Valve
W	Weight or force		Well
X	Danger	Axis X	Unclassified	Unclassified	Fault
Y	Event	Axis Y		Calculation module (5)
Z	Position or dimension	Axis Z		Unclassified final element

Notes:

1. User choice letters must be chosen uniquely for each project. For example C = Conductivity; D = Density; etc.
2. Glass instruments allow the visualization of process data
3. Very high or maximum is indicated with HH
4. Very low or minimum is indicated with LL
5. To define the Y function on a diagram, add the specific symbol of the relay or convert to a square of 6 mm on the side of the graphical sign of the instrument (in the north-east position)

Table 2 - Instrumentation Valve Symbols

Table 3 - Actuators for Instrumentation Valve Symbols

Actuators for instrumentation valve symbols

Table 4 - Identification of Safety Conditions for Valves and Actuators (Without Supply)

Symbology for Power Supply

Symbol	Meaning
AS	Air Supply
IA	Instrument Air
PA	Plant Air
ES	Electrical Supply
GS	Gas Supply
HS	Hydraulic Supply
NS	Nitrogen Supply
SS	Steam Supply
WS	Water Supply

Symbology for Instrumentation Signals

The table shows the symbology of control signals for instrumentation

Symbology for instrumentation signals

P&ID SYMBOLS PDF You can download most P&ID symbols in PDF format by clicking on the following link:

Download P&ID symbols for piping (originally available at projectmaterials.com)

Instruments (P&ID Symbols)

Analyzer Transmitter	AND Gate	Averaging Pitot Tube
Behind Control	Behind Local Control	Computer
Computer Indicator	Coriolis Flow Sensor	Correcting Element
Diamond	Diaphragm Meter	Displayed Configurable
Displayed Programmable Indicator	Double	Flow Controller
Flow Element	Flow Indicator	Flow Meter
Flow Nozzle Meter	Flow Recorder	Flow Transmitter
Flowmeter	Flume Meter	Indicator 01
Level Alarm	Level Controller	Level Gauge
Level Indicator	Level Meter	Level Recorder
Level Transmitter	Magnetic Flow Meter	Manhole
NOT Gate	Odometer	On Central Control Panel
On Local Control Panel	OR Gate	Pitot Tube
Pitot Tube Type Flow Meter	Pressure Controller	Pressure Gauge
Pressure Gauges	Pressure Indicating Controller	Pressure Indicator
Pressure Recorder	Pressure Recording Controller	Pressure Transmitter
Programmable Indicator	Quick Change Meter	Rotary Meter
Rotometer	Sampler	Shared Indicator 01
Shared Indicator 02	Socket Connection	Specialty Item
Steam Tracer	Straightening Vane	Support Bracket
Support Leg	Support Ring	Support Skirt
Target Meter	Temperature Controller	Temperature Element
Temperature Indicator	Temperature Recorder	Temperature Transmitter
Thermometer	Thermometers	Transducer
Turbine Meter	Ultrasonic Meter	Unit Control Panel
V Cone Meter	Venturi	Venturi Meter
Vortex Sensor	Wedge Meter	Weir Meter

Frequently Asked Questions

What standard defines P&ID symbols?

The two main standards are ISA S5.1 (ANSI/ISA-5.1, widely used in North America and oil & gas globally) and ISO 14617 (used in Europe and international projects). ISA S5.1 defines instrument identification, tag numbering, and graphical symbols for process instrumentation and control. Most EPC contractors use ISA-based symbology, sometimes supplemented with company-specific legend sheets.

What do dashed lines represent on a P&ID?

Dashed lines on a P&ID typically represent signal or communication lines ; not process piping. A single dashed line usually indicates a pneumatic signal, a dashed line with dots indicates an electrical signal, and a double dashed line indicates a software/data link. Process lines carrying fluids are always drawn as solid lines, with line weight indicating main process vs. utility lines.

How are valve actuator types shown on P&ID drawings?

Valve actuator types are indicated by symbols added to the top of the valve symbol: a filled triangle for a pneumatic diaphragm actuator, an open triangle for a piston actuator, a circle with M for a motor operator, a diamond for a solenoid, and a T-handle for a manual handwheel or gear operator. The fail-safe position (fail-open, fail-closed) is annotated next to the actuator symbol.

What is the difference between ISA S5.1 and ISO 14617 symbol standards?

ISA S5.1 uses a bubble (circle) with letter codes inside to identify instruments (e.g., "FT" for flow transmitter, "PIC" for pressure indicating controller). ISO 14617 uses a different graphical convention with rectangular function blocks. ISA symbology is dominant in oil & gas and petrochemical industries worldwide. ISO 14617 is more common in European process and power industries. Most international EPC projects default to ISA-based legends.

Download P&ID Symbols (PDF)

This P&ID symbols library contains 407 symbols across 12 categories (piping, valves, strainers, lines, equipment, pumps, compressors, heat exchangers, vessels, motors, filters, and ISA instruments). All symbols follow ISA S5.1 and ISO 14617 standards and can be used as reference for P&ID drawing, engineering documentation, and training.

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