Flow process chart: the 5 symbols to map any process

In one line

A flow process chart (or process flow diagram) follows the real path of a part, a form or a person through a process, and classifies each step under just 5 symbols: Operation, Transport, Inspection, Delay and Storage.

What it is

The source distinguishes two tools that are often confused because they look alike at first glance. The first is the operation process chart (or outline process chart): it uses only two symbols, a circle for each operation and a square for each inspection, and it shows the complete process of an assembly from the moment the raw material arrives to the finished product. It is the panoramic view.

The second, more detailed, is the flow process chart proper: it is applied component by component (not to the entire assembly) and adds three more symbols so you can record the "hidden" times that add no value — distances traveled, waits and temporary storage. These 5 symbols are the 1974 ASME standard that the source quotes verbatim, and Spanish-language literature also calls it the OTIDA diagram, after the initial of each activity (in English the equivalent acronym would be OTIDS):

Symbol	Activity	What it represents
○ Circle	Operation	The part is transformed, assembled or deliberately planned (includes planning or studying before working on it).
→ Arrow	Transport	It moves from one place to another — except for movement that is already part of an operation or inspection.
□ Square	Inspection	It is examined to verify that it meets a quantity or quality standard, without transforming it.
D	Delay	The part sits waiting because it cannot move on to the next station right away.
▽ Triangle	Storage	It is kept and protected in one place, and nobody can remove it without authorization.

This second source places the flow process chart among what it calls the methods engineer's "schematic aids": diagram-based techniques for describing and communicating a work method, alongside the precedence diagram or the man-machine chart. It agrees that its value lies in overlaying the same ASME process-analysis symbols on the real sequence followed by the object of study, giving a compact view of an existing or proposed process.

There are two variants depending on what you follow with your eyes: a product or material diagram (you follow a part, a batch or a form) and an operator flow diagram (you follow a person — an operator, a technician, a delivery person — while they carry out their sequence of tasks). The construction is identical; only the subject being followed changes.

What it is for

In any process, the only thing a customer pays for is the Operation: everything else — transporting, waiting, inspecting, storing — is time that piles up without adding value. The problem is that, without a formal record, those times stay invisible: nobody times how long a part waits "next to the machine" or how many extra meters it travels. The flow process chart forces you to write down each of those events with its symbol, its time and its distance, so it turns something that used to be a vague feeling ("this takes too long") into a summary with concrete numbers for each type of activity.

Since it is also built following the real chronological order of the process, the finished diagram already suggests an ideal plant layout: it shows which activities should sit close to one another to minimize transports. Niebel documents a historical case of this at the Springfield Armory: by building a flow process chart and its companion flow diagram for the M1 Garand rifle, production went from 500 to 3,600 barrels per shift with the same number of employees — the improvement did not come from working faster, but from eliminating the transports, waits and travel that the diagram exposed.

How to apply it

1. Choose what you are going to follow. A part, a batch, a form (material diagram) or a person doing their task (operator diagram). The flow process chart always follows a single subject from start to finish — it does not mix several parts in the same diagram.

2. Fill in the header. Before walking through anything, identify the diagram: title, part or drawing number, description of the process, whether it is the current method or a proposed one, date and who prepared it. This information lets you compare a "before" against an "after" later on.

3. Physically walk the process. You have to walk through the real process (or at least watch it from end to end) and write down each event in the exact order in which it happens, not as it is supposed to happen on paper.

4. Classify each event with its symbol. For each step: is the part transformed? Operation. Does it move? Transport. Is it checked without being transformed? Inspection. Does it sit waiting? Delay. Is it kept under control? Storage. Consecutive symbols are joined by a vertical line, in the order in which they occur.

5. Record time and distance. Each operation, inspection or delay is assigned a time (estimated or measured with a stopwatch); each transport, in addition, gets a distance. You do not need tape-measure precision for the distance: it is enough to count how many columns or sections of the floor plan the object crosses and multiply by the distance between them — movements of less than about 1.5 meters are usually omitted, unless they are repeated many times.

6. Build the summary. When you close the diagram, count how many events there were of each type, and add up the total times and distances. That summary is the first thing you look at to decide where to attack: normally, the biggest improvement opportunity is in reducing transports, delays and storage — not in speeding up the operations.

7. Overlay it on a floor plan (optional but recommended). The flow process chart only shows the logical sequence; it does not say where each thing sits inside the plant. For that there is its geographic companion: the flow (or route) diagram, which draws the same path on a real plan of the plant — the direct ancestor of what is known today as the spaghetti diagram. One shows the logic of the process; the other shows where each symbol physically occurs and how tangled the route ends up on the plan.

Real or illustrative example

Illustrative example: the sources consulted bring their own cases (a telephone base in Niebel, a corrugated pipe in Krick), but with column formats that cannot be reproduced exactly outside the original chart. The following flow process chart was built for this note, following the same column format — symbol, description, time, distance — that both sources use, on a typical maintenance case: replacing a bearing.

Process followed: one bearing, from the moment it leaves the spare parts warehouse until the old bearing is stored for failure analysis.

Symbol	Activity description	Time	Distance
▽ Storage	New bearing in the spare parts warehouse	—	—
→ Transport	Carried from the warehouse to the maintenance shop	3 min	40 m
□ Inspection	Part number and dimensions checked against the work order	2 min	—
D Delay	Wait until production releases the machine	15 min	—
→ Transport	Carried to the machine	4 min	60 m
○ Operation	Old bearing is removed	20 min	—
□ Inspection	Condition of the shaft seat is checked	5 min	—
○ Operation	New bearing is installed	25 min	—
○ Operation	Adjusted and lubricated	10 min	—
□ Inspection	Startup and vibration test	8 min	—
▽ Storage	The old bearing is stored for failure analysis	—	—

Summary:

Symbol	Count	Total time	Total distance
○ Operation	3	55 min	—
→ Transport	2	7 min	100 m
□ Inspection	3	15 min	—
D Delay	1	15 min	—
▽ Storage	2	—	—
Total	11	92 min	100 m

Of the 92 total minutes, barely 55 (60%) are Operation — the only thing that actually repairs the equipment. The rest (37 minutes, 40%) is transport, inspection and a 15-minute delay waiting for the machine to become free. That number is exactly what a flow process chart exposes as the first thing to attack: can you coordinate with production beforehand so the 15-minute delay does not exist, or can you move the warehouse for critical spare parts closer to the shop to cut the 100 meters of transport?

Template to use

Before walking through the process, fill in these header details:

• Process / part followed:
• Method: Current or Proposed
• Analyst and date:

And for each step of the walkthrough, one row with these columns:

Symbol (○ → □ D ▽)	Activity description	Time	Distance

At the end, close with the summary: number of events, total time and total distance for each of the 5 symbols.

So you do not have to build it by hand, there is a flow process chart and spaghetti diagram spreadsheet in Excel with the formulas already in place: for each of the 5 symbols it summarizes the events, the time and the distance. The values it comes with are examples and you need to delete them.

Benefits

• With just 5 symbols, anyone on the shop floor can draw it up and read it without prior statistical training.
• It makes visible the time that adds no value (transport, delay, storage) — the time that almost never gets counted without a formal record.
• The chronological order of the symbols already hints at a shorter plant layout: which activities should be moved closer together.
• It works both for following a part or a material and for following a person doing their sequence of tasks — the same tool, two variants.

Limitations to keep in mind

• You have to walk through the real process; drawing it from memory at a desk is not enough — for long processes, building it properly can take several hours.
• It only records the logical sequence: it does not show where each activity sits inside the plant or the traffic crossings between flow lines — for that you need to overlay it on a floor plan (flow or route diagram / spaghetti diagram).
• Distances are approximate by design (you count floor plan columns, you do not measure with a tape), so it is not suitable for calculations that need millimeter precision.
• The diagram describes the current method; by itself it does not say what to change. Operations analysis is needed afterwards — asking why each transport, each delay, each storage exists — to turn it into a real improvement.

In summary

The flow process chart (or process flow diagram, OTIDA in Spanish-language literature) follows a part or a person step by step and classifies each event under 5 symbols: Operation, Transport, Inspection, Delay and Storage. Unlike the operation process chart —which looks only at operations and inspections—, this diagram puts numbers on what normally stays hidden: how much is transported, how much is waited, how much is stored. It is the logical, sequential map of the process; its physical, geographic complement is the flow or route diagram, the direct ancestor of the spaghetti diagram.