Block Flow Diagram

Written by Jerry Ratzlaff. Posted in Designer

A block flow diagram or a block schematic diagram is a simplified representation of a [[Process Flow Diagram]].  Unit operations or processes may be represented by rectangles or by a CAD block of the piece of equipment.  Each block shows an activity, such as storage or treatment, performed on the primary streams only.Blocks are connected by straight lines and flow arrows and represent a mixture of liquids, gasses or solids moving through the facility.  Similar to PFDs, a Block Flow Diagram does not show bypasses, secondary lines or line numbers.  

The PFD displays the relationship between major equipment of a plant facility and does not show details such as minor equipment items, piping materials of construction and piping sizes.  An example of a BFD is shown to the right.  Note that the process flow is easily distinguishable, contains no instrumentation or controls.  

In order to create a well versed Block Flow Diagram, the following process is recommended.

  • Place all major pieces of equipment and unit operations. When multiple pieces of equipment exist in parallel, they may be shown as a single item.  The equipment need not have numbers but should show the process or operation that it conducts.
  • Connect the pieces of equipment with straight primary lines and show flow arrows. 
  • Flow direction should always go left to right.  If they cross, the horizontal line takes precedence over the vertical line.
  • Light stream (gases) toward top with heavy stream (liquids and solids) toward bottom.
  • Only the most critical process information needs to be supplied.  This could be the name of the product or function.


  • BFD - Block Flow Diagram