Posted At: Nov 20, 2025 - 99 Views
API Plan 11 vs API Plan 23: What’s the Difference and When to Use Each?
Introduction
Mechanical seal reliability is critical for pump performance, especially in industries handling high-temperature, hazardous, or viscous fluids. The API (American Petroleum Institute) has defined several seal piping plans to improve cooling, lubrication, and seal life. If you need to know more about QMseals click here.
Two of the most commonly used options are API Plan 11 and API Plan 23.
While both are circulation plans designed to protect the mechanical seal, they work differently and are suitable for different pump applications. This guide explains the difference between API Plan 11 and API Plan 23 and when you should use each.
What Is an API Plan?
An API plan is a standardized piping configuration used to improve mechanical seal performance.
It defines how fluid moves around the seal to provide cooling, flushing, pressure control, or debris removal.
Common benefits of pump seal plans include:
Better seal lubrication
Reduced heat generation
Improved reliability
Longer mechanical seal life
Lower maintenance costs
What Is API Plan 11?
API Plan 11 is the simplest and most widely used flushing plan. It takes fluid from the pump discharge and sends it to the mechanical seal chamber for cooling and lubrication.
How API Plan 11 Works
Flush line is connected from the pump discharge to the seal chamber.
A flow control device (like an orifice) regulates the flush.
Hot process fluid circulates continuously.
Best Used For
Clean fluids
Moderate operating temperatures
Pumps with standard seal chambers
General-purpose chemical, water, and oil transfer applications
Advantages of API Plan 11
Simple design
Easy installation
Low cost
Effective for clean, stable fluids
Limitations
Not suitable for extremely high temperatures
Hot process fluid may cause thermal stress on seals
What Is API Plan 23?
API Plan 23 is designed for high-temperature applications where additional cooling is needed.
It uses a circulation loop with an internal heat exchanger to cool the fluid before it reaches the seal.
How API Plan 23 Works
Fluid circulates from the seal chamber, through a heat exchanger, and returns cooled.
Circulation is often achieved using the pump’s internal pumping ring.
Only a small portion of product fluid circulates in this loop.
Best Used For
High-temperature fluids
Hot hydrocarbons
Chemical processing
Boiler feed pumps
Applications above 180°C (or when API 682 recommends a cooler plan)
Advantages of API Plan 23
Excellent cooling efficiency
Lower seal chamber temperature
Minimizes coking or vaporization at the seal faces
Extends seal life in high-temperature services
Limitations
Slightly higher installation cost
Requires a cooler and proper piping layout
API Plan 11 vs API Plan 23: Key Differences
| Feature | API Plan 11 | API Plan 23 |
|---|---|---|
| Fluid Source | Pump discharge | Seal chamber (recirculation loop) |
| Cooling Level | Moderate | High |
| Heat Exchanger | Not required | Required |
| Applications | Clean and moderate-temperature fluids | High-temperature or thermal-sensitive fluids |
| Cost | Lower | Higher |
| Seal Protection | Basic | Superior in high heat |
When to Use Each Seal Plan?
Use API Plan 11 When:
The pumped fluid is clean
Temperature is moderate
There is no risk of vaporization or coking
You need a simple, cost-effective flushing solution
Use API Plan 23 When:
Pumping high-temperature fluids
Seal face cooling is a priority
Process fluid may vaporize near the seal
You need longer seal life under thermal stress
Conclusion
Both API Plan 11 and API Plan 23 play an essential role in improving mechanical seal reliability.
- API Plan 11 is ideal for general-purpose pumps and clean fluids.
- API Plan 23 is the best choice for high-temperature applications requiring maximum cooling.
Choosing the right api plan enhances seal performance, reduces downtime, and extends the life of your pumping system.
Frequently Asked Questions
1. What is the main difference between API Plan 11 and API Plan 23?
API Plan 11 uses pump discharge fluid for seal flushing, while API Plan 23 uses a cooled, recirculating loop with a heat exchanger for better temperature control.
2. Which seal plan is best for high-temperature fluids?
API Plan 23 is recommended because it provides superior cooling through a heat exchanger.
3. Is API Plan 11 suitable for all pumps?
It works well for pumps handling clean, moderate-temperature fluids but should not be used for very hot or thermally sensitive applications.
