Multistage Centrifugal Pump P&ID Symbol Explained (Engineering Guide)
Multistage Centrifugal Pump Symbol in P&ID Drawing (Complete Engineering Guide)
II JAY SHRI KRISHNA II
 |
Multistage centrifugal pump with P&ID symbol representation |
In piping engineering, understanding P&ID symbols is not optional — it is essential.
One of the most common technical questions asked by students, site engineers and even fresh design engineers is:
“Which symbol is used for a multistage centrifugal pump in P&ID, 2D drawings?”
This may look like a simple question, but the answer is very important for correct drawing interpretation.
If you misunderstand pump symbols, you can:
- Misread system pressure
- Assume wrong equipment type
- Make inspection mistakes
- Approve incorrect installation
In this detailed guide, we will clearly explain:
- The standard symbol used for centrifugal pumps
- Whether multistage pumps have a different symbol
- Why P&ID does not show internal stages
- How to identify multistage pumps in real projects
- Relevant international standards
- Practical site examples
Let us start from the basics.
What Is a Multistage Centrifugal Pump?
 |
Internal construction showing multiple impellers |
A multistage centrifugal pump, is a pump that contains two or more impellers inside a single casing.
Every impeller stage progressively increases the fluid pressure as it passes through the pump. When these impellers are connected in series:
- The total head increases
- Higher discharge pressure is achieved
- It becomes suitable for high-pressure systems
Common Applications:
- Boiler Feed Water Systems
- Fire Water Systems
- Reverse Osmosis (RO) Plants
- High-Rise Building Pressure Boosting
- Process Plants requiring high head
In simple words:
Single-stage pump = Normal pressure
Multistage pump = High pressure
What Is a P&ID?
P&ID stands for Piping and Instrumentation Diagram.
It is a functional diagram that shows:
- Pumps
- Instruments
- Flow direction
- Control loops
- Safety devices
Important:
A P&ID is NOT:
- A 3D drawing
- A fabrication drawing
- A mechanical cross-section drawing
- It only shows how the system functions.
That's why internal details, like impellers are usually not shown.
Standard Centrifugal Pump Symbol in P&ID
According to international standards, the main references are:
- ISA S5.1 – Instrumentation Symbols and Identification
- ISO 14617 – Graphical Symbols for Diagrams
Both standards use a standard centrifugal pump symbol, without separate marking for multistage pump.
Always follow project specification.
The standard centrifugal pump symbol consists of:
- A circle (representing the pump body)
- A small triangle or arrow inside (showing, flow direction)
- Suction and discharge lines connected
Basic meaning:
Circle = Pump casing
Triangle = Flow directionLines = Inlet and outlet piping
This is the universal symbol used worldwide.
 |
Standard centrifugal pump symbol in P&ID |
Does a Multistage Centrifugal Pump, Have a Special Symbol?
❗ The correct technical answer is:
No.
Within P&ID diagrams, multistage centrifugal pumps are represented by the same basic pump symbol, as no separate symbol is used to indicate multiple stages.
- The Symbol: A circle with inside solid triangle, is the industry standard representation for a centrifugal pump.
- Flow Direction: The internal triangle serves as a directional guide; by pointing toward the discharge piping.
There is:
- No special stacked symbol
- No multiple triangles inside
- No internal stage marking
- No separate graphical shape
Whether the pump has:
- 2 stages
- 4 stages
- 8 stages
- 12 stages
The symbol remains the standard centrifugal pump symbol.
This is because:
P&ID focuses on function — not internal construction.
Why P&ID Does Not Show Internal Stages
Many students make this mistake:
They think multistage pump should show multiple internal arrows.
However, this is incorrect in standard engineering practice.
Remember:
P&ID shows:
- Flow path
- Process control
- Isolation philosophy
- Safety devices
It does NOT show:
- Number of impellers
- Internal shaft design
- Bearing type
- Seal arrangement
Those details are found in:
- Mechanical drawings
- Vendor GA drawings
- Equipment datasheets
- Cross-section diagrams
Then How Do We Identify It Is Multistage?
Since the symbol does not change, how do we know it is multistage?
There are three professional ways:
1️⃣ Pump Tag Number
Example:
- P-401
- P-204A/B
The P&ID only shows the tag.
 |
Pump tag identification in P&ID drawing |
Tagging example (P-401): In standard practice, the letter “P” represents a pump, while the number “401” is a unique equipment identifier. This tag helps engineers quickly locate and reference the pump in drawings and documents.
Then you check:
- Pump schedule
- Equipment list
- Mechanical datasheet
There you will see:
Type: Multistage Centrifugal
Stages: 4
Head: 150 m
2️⃣ Equipment Datasheet
The number of stages is clearly mentioned in:
- Vendor documents
- Technical bid evaluation
- Purchase specification
3️⃣ Sometimes Additional Notation
Some companies may write near the pump:
4 STG PUMP
Technical markings often depend on proprietary company standards rather than strict international mandates.
Important Tip: Even though ISA and ISO symbols serve as a universal language, the Project Legend remains your ultimate source of truth. It is common for specific engineering firms to adopt unique notations that highlight multistage units, ensuring that field personnel can immediately identify high-pressure equipment without cross-referencing datasheets.
Common Mistake Engineers Make
Many beginners assume:
Many beginners believe that high-pressure pumps should have a different symbol, but this is incorrect and can lead to confusion during design reviews and site discussions.
Remember: This is wrong.
Pressure level does not change the P&ID symbol.
The P&ID symbol shows the equipment type used, not its operating conditions such as, pressure / capacity.
Difference Between PFD and P&ID for Pumps
PFD (Process Flow Diagram)
- Simplified drawing
- Shows major equipment only and
- Less detail
P&ID
- Detailed functional diagram
- Shows instruments
- Shows drains, vents, bypass lines
- Shows control valves etc.
But in the both PFD and P&ID drawings, symbol of centrifugal pump showing remains the same.
Practical Site Example:
Let us take a Boiler Feed Water Pump.
On P&ID, you see:
Circle with triangle
Tag: P-301
From the drawing alone, you cannot confirm:
- Number of stages
- Mechanical seal type
- RPM
When you go to equipment datasheet, it will show:
Type: Horizontal Multistage Centrifugal
Discharge Head: 180 meters
So always cross-check documents.
Why This Knowledge Is Important?
Understanding correct pump symbol usage helps you:
- Avoid design confusion
- Read drawings confidently
- Pass interviews easily
- Perform better in QA/QC inspections
- Understand pressure zones correctly
- For site engineers, this prevents costly mistakes.
- For design engineers, this ensures drafting consistency.
From practical experience in piping design projects, many engineers initially expect a different symbol for multistage pumps. However, international standards do not support this assumption.
Conclusion:
✅ Standard drafting protocols dictate that a multistage centrifugal pump utilizes the universal centrifugal icon—a clean circle with an integrated arrow to specify the flow path—regardless of the number of internal stages.
❌ There is no separate / unique symbol for multistage pumps in standard ISA or ISO P&ID drawings.
The number of stages is specified in:
- Equipment datasheet
- Pump schedule
- Vendor documentation
- Mechanical drawings
- Not in the P&ID symbol itself.
In piping engineering, clarity means safety and efficiency.
The P&ID purpose, is to represent the overall process flow & interaction between system components, rather than showing the internal design of individual equipment.
Whether the pump is:
- Single-stage
- Two-stage
- Multistage high-pressure
- The graphical symbol remains the same.
Experienced engineers never guess; they verify. While beginners may assume details based on symbols, experts cross-reference equipment datasheets to ensure precision. Solidifying your technical foundation in this way is the most reliable path to building confidence, whether you are answering questions in a high-stakes interview or managing complex site work.
If you have any questions related to piping engineering, feel free to write your question in the comment section of our website. We'll try to give you correct technical answer.
Your question may also help other engineers who have the same doubt.
If you want to strengthen your foundation further, you can also read our detailed technical guides at:
👉 https://www.knowpipingfield.com/
Suggested Further Reading:
Understanding Piping Material Specification (PMS): The Engineer’s Guide
Centrifugal Pump: High-Flow with Motion Accuracy
Understanding Cavitation in Centrifugal Pumps: Causes and Preventions
Single Stage and Multistage Centrifugal Pumps: A Comprehensive Guide and Comparison
Centrifugal Pumps Varieties: Axial Flow, Radial Flow and Mixed Flow
Overview of Vertical, Horizontal and Submersible Centrifugal Pump
Specialized Centrifugal Pumps Technologies: Self-Priming, Cryogenic and Chemical Variants
AI-Driven Piping Design: Machine Learning Transformation
Piping Digital Twin: Complete Guide
Piping Layout and Design Best Practices: A Comprehensive Guide
Best Practices for Header & Nozzle Loads in Piping Systems
Thank you so much for following my blog…!! 🙏See you all in the next coming blogs — till then, keep exploring the piping field!
Have a great day — keep smiling 😀 and God Bless You all…!!
To be continued…
Post a Comment