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P&ID Valve Symbols: How to read them on most common control valves?


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Valve symbols in process and instrumentation diagrams

What is P&ID?

The process flow diagram (PFD), which explains a relatively typical flow of plant processes about significant equipment of a plant facility, and the piping and instrumentation diagram have a close relationship. According to wiki, A piping and instrumentation diagram shows a processing plan’s piping, process equipment, instrumentation, and controls. Pipes and other aspects of a physical process flow are shown. These diagrams are popular in engineering.


PFD shows process engineers how chemical fluids travel through a chemical process’s major equipment. The process flow schematic doesn’t depict a plumbing facility or pressure-flow instruments. P&IDs build, manage, and repair chemical processing plants. Piping, mechanical, civil, electrical, and instrumentation engineers use them extensively.

How does P&ID work?

P&ID symbols and codes indicate each process instrument. This code and symbol can help us identify the device, its location, and its role in the process. Iso standard for P&ID symbols instruments and identifying letter codes are needed to read P&IDs.

Piping and instrumentation diagram example

P&ID Sample

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Material processing P&IDs include all physical component details:

  • Process equipment specifications (turbines, fans, vessels, pumps, etc.)
  • Piping and line specifications and process piping system components (fittings, flanges, valves, actuators, insulation, etc.);
  • Indicators, gauges, alarms, interlocks, control input, and output.

What do P&ID & PID Symbols Include?

P&IDs use standard shapes and symbols:

  • Equipment Symbols

P&ID equipment consists of several pieces that don’t fall into the categories of other items.

  • Piping Symbols

Plastic or metal pipes transfer liquids/gasses. 

  • Vessel Symbols

Vessels alter fluid properties. 

  • Heat Exchanger Symbols

Heat exchangers transport heat between areas. 

  • Pump Symbols

Pumps transfer fluids between objects. 

  • Instrument Symbols

Instruments measure temperature, flow, tilt, pressure, etc. 

  • Valve Symbols

They regulate fluid flow by shutting, opening, or gently obstructing piping channels. 

Valve symbols on P&ID

Valve Symbols

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They manage fluid flow by closing, opening, or slightly obstructing channels in a piping setup, much like the valves in our hearts. Rotameters, orifices, and various types of valves fall under this category.

Types of valves with P&ID symbols

A valve is an element in a piping system that regulates the flow.

  • A rotary valve turns only at 90°
  • Linear valves operate when the stem is vertical, and the packing box is above.
  • Self-actuated valves keep set-point pressure in pipelines within predetermined ranges.

P&ID valve symbols: How to read?

The comprehensive engineering procedures are described using a P&ID. Below are some ways that will help you in reading them:

  1. Download the P&ID symbols and meaning
  2. Familiarize the symbols
  3. Practice with a sample online 
  4. Consult an expert

2-way valve symbol

2-way valve

Image Source: Assured Automation

Two-way ball valves block between two cup-shaped seals called “seats.” Open media passes through straight bores in balls. The ball stops media flow when rotated 90°.

3 & 4-way valve symbols

 3 & 4-way valve

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A 3-way valve lets fluid flow to and out of an actuator. The third position on some 3-way valves shuts all ports. Double-acting actuators need 4-way valves. A 4-way valve simultaneously pressurizes and exhausts two openings.

Other types of valve symbols



Image Source: EnggCyclopedia

Actuators transform control signals into mechanical motion using power. Actuators are everywhere—from car door locks to airplane ailerons.

End connections 

End cap

Image Source: Electra Cloud


The flange’s end connection provides a compact and efficient link between the valve and pipe, which describes how the flange is joined to a nearby line.

Process lines

 Process Line

Image Source: Nikolay Bozov


Any coating unit, line, operation, or printing press is a process line. Process lines are one or more activities or unit operations that must coincide or be in sequence to manufacture or change a product.

Signal lines 

 Instrument signal

Image Source: Engineers Community

Signal lines identify how the instruments in the process connect. And what type of signal is being used.


Vessel symbols

Image Source: Hardhat Engineer

A vessel is used to illustrate a fluid storage container. Tanks, cylinders, columns, bags, and other items for bigger ships are included in the P&ID symbol group.

Other common P&ID Symbols for major process components

Tag numbers 

Tag number

Image Source: Learning Instrumentation and control engineer

The project’s equipment and tagged items are identified by a tag number, assigned, and used on nameplates, drawings, datasheets, and all correspondence.

The symbol for a valve

Ball valve P&ID symbol

Ball valve

Image Source: Assured Automation

A ball valve shuts off liquid or gas flow using a rotary ball with a bore.

Butterfly valve P&ID symbol

 Butterfly valve

Image Source: Assured Automation

Quarter-turn rotational motion butterfly valves shut off pipeline flow. Butterfly valves can control flow.

Gate valve symbol P&ID

Gate valve

Image Source: Assured Automation

In the fully open position, a gate valve allows full pipeline flow or entirely stops it.

Globe valve P&ID symbol

Globe valve

Image Source: Assured Automation

Globe valves regulate flow, pressure, and flow shutdown. It can also be a check or pressure relief valve.

Plug valve P&ID symbol

 Plug valve

Image Source: Assured Automation

Plug valves are ideal for directional flow control, gas or liquid fuel handling, slurry regulation, and low-pressure, low-temperature services.

Solenoid valve symbol

Solenoid valve

Image Source: Your Electrical Guide

Fluidics uses solenoid valves the most. They stop, release, dose, distribute, or mix fluids.

Relief valve symbol

Relief Valve

Image Source: Hardhat Engineer

Needle valve symbol

Needle valve

Image Source: Assured Automation

Needle valves regulate gas or water flow in appliances and systems.

Safety valve symbol

safety valve

Image Source: EnggCyclopedia

The Safety Valve is the last line of defense against system pressure failure, protecting life and property.

Angle valve symbol

 Angle valve

Image Source: Electra Cloud

Angle valves are utilized in boiler feedwater, heater drain, and space-constrained piping schemes as elbows.

Float valve symbol

Float valve

Image Source: Advanced 3D Solutions

Float valves can prevent tanks from overfilling when liquid needs to be diverted rather than discharged in a drain.

Pinch valve symbol

Pinch valve

Image Source: Assured Automation

A pinch valve is a 2/2-way valve that stops or controls corrosive, abrasive, or granular material.

Bleed valve symbol

Bleed valve

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Bleed valves manually drain liquids or gases from instruments or systems. These valves provide vent tube-controlled outflow direction.

Knife gate valve symbol

 Knife Gate valve

Image Source: Electra Cloud

Knife gate valves isolate and turn off suspended solids-rich systems. Slurry, viscous, corrosive, and abrasive media suit knife gate valves.

Piston valve symbol

Piston valve

Image Source: Electra Cloud

Power plants, refineries, pulp, and paper mills employ piston valves for saturated and superheated steam and hot water.

P&ID valve symbols: in summary 

P&IDs are crucial information transmitters during design. It communicates. Process diagrams convey various engineering information to numerous organizations for many purposes. The chemical process industry values PFD and P&ID preparations. These diagrams show process engineers’ inventive designs. Preparation can save money, improve plant layout, and improve safety.

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