181 Process Flow Diagram (PFD) Symbols for Engineers
Welcome to our process flow diagram symbols list. Scroll down and use the table of contents on the left to navigate this page and see the different symbol types most commonly used by engineers.
But first, let’s review the purpose and benefits of a PFD.
The Purpose and Benefits of a Process Flow Diagram
The use of different types of flowcharts and diagrams provide a number of benefits and purposes including:
- An easy to understand structure, for high-quality control and in-depth training
- Being able to standardize a process for optimal efficiency, repetition, and use
- To aid the study of efficiency and improvement in a process, highlight areas of inefficiency, bottlenecks, and unnecessary steps in a diagram
- To model a new or improved process
- To communicate and collaborate on a number of projects
Process Flow Diagram Equipment Symbols
Flow chart symbols use different shapes to represent different components, such as equipment, valves, instruments, and piping flow. There is a standardized set of flowchart symbols.
Process Flow Diagram equipment symbols include centrifuges and heat exchangers.
Centrifuges are devices that use centrifugal force/ acceleration to separate components of a mixture on the bases of their density, size, viscosity, and rotor speed. The more dense molecules move to the outside of the centrifuge and the less dense molecules move towards the centre.
Heat exchangers are a system that transfers heat between 2 or more fluids, separated by a solid wall. Heat exchangers can be used for both cooling and heating processes.
Miscellaneous PFD Symbols
Miscellaneous PFD symbols include crushers, dryers, general, mixers, and peripherals.
Crushers are used to reduce the size of or change the form of materials, often for waste, to be deposited or recycled. They reduce the size of a solid mix of raw material.
Dryers are components used to dry fluids through different processes.
General PFD Symbols
There are a number of other standard symbols included in PFD diagrams with a multitude of functions, as shown below.
Mixers are used to combine 1 or more fluids to create a mixture.
Peripheral PFD Symbols
Peripheral PFD symbols represent devices that are not core components used in the flow diagram.
Piping fittings are adaptors used to connect straight sections of pipe or tube in a pipe system to create the required geometry.
What is a Process Flow Diagram?
A process flow diagram is a flowchart that depicts the relationships between major components in a process or circuit. The concept originated in 1921 - it was designed by industrial engineer Frank Gilbreth. Today the concept is often used in industrial plants for chemical and process engineering but the concepts can also be applied to a number of other applications.
Process flow diagrams consist of a series of flowchart symbols and notations to illustrate a process. The different types of flowcharts can vary hugely from hand-drawn flowcharts to complex software flowcharts.
What's Included in a Process Flow Diagram?
For a single unit process, the flowchart diagram includes:
- Process piping
- Major equipment items
- Operational data (pressure, temperature, etc.)
- Major bypass
- Process stream names
To reduce over-annotating a process flow diagram, there are a number of aspects that aren't included:
- Pipe classes and line numbers
- Minor bypass lines
- Instrumental details
- Isolation and shut off valves
- Controllers (such as a flow controller)
- Maintenance vents and drains
- Relief and safety valves
What is a Process Flow Diagram Used for?
Process flow diagrams can be used to document a predefined process, improve an existing process, or model a new process. Process flow diagrams can also be known as:
- Process Flow Chart
- Plumbing & Instrumental Diagram
- Macro Flowchart
- Top-Down Flowchart
- Block Flow Diagram
- Schematic Flow Diagram
- System Flow Diagram
- System Diagram
What is the Process Symbol in a Flowchart?
Process symbols represent an action, process, or function. They are also referred to as an 'action symbol' and are the most commonly used symbols in flowcharting. These types of symbols are often used in software.
How to Create a Process Flow Diagram
Here are 6 steps to create a process flow diagram:
- Define the scope of the system, what will it achieve?
- Determine the process boundaries, what causes it to start? Where does it end? What are the boundaries of the process?
- Identify the process outputs, what is the final goal?
- Identify the inputs, are there any manual inputs? What is required at each step?
- Use this data to create a model, add necessary detail such as control points and measurements. Think methodically how do components interact with one another.
- Add process symbols to describe the component/ equipment.
- Create a data dictionary, outlining data omitted from the flowchart.
- Review, revise, and test when necessary.
What are Process Flow Diagram Standards?
There are a number of standards related to process flow diagrams in industry, to ensure adequate representation of engineering systems. The most common standards are:
- ISO 15519-1:2010(en): Specification for diagrams for the process industry — Part 1: General rules
- ISO 15519-2:2015(en): Specifications for diagrams for the process industry — Part 2: Measurement and control
- ISO 10628-1:2014(en): Diagrams for the chemical and petrochemical industry — Part 1: Specification of diagrams
- ISO 10628-2:2012(en): Diagrams for the chemical and petrochemical industry — Part 2: Graphical symbols
What Are Basic Flowchart Symbols?
For software-based process flow diagrams, there are a number of basic symbols to identify. These include:
- Oval - input/ output of the system
- Rectangle - a step in the process
- Arrows/ lines - indicate directional flow
- Diamond - represents a decision
These symbols are not commonly used in engineering diagrams such as mechanical, chemical, and electrical process flow diagrams. These symbols, however, can be found in computer software.