API Plan 21
API Plan 21 – Discharge Recirculation with Cooling
API Plan 21 is a mechanical seal flush plan that takes process fluid from the pump discharge, passes it through a cooler, and then directs it into the seal chamber.
This system is designed to provide cooler process fluid for lubrication and temperature control, making it more effective than API Plan 11 in high-temperature applications.
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Features
How It Works:
- Fluid is drawn from the pump discharge (high-pressure region).
- It passes through a flow control orifice to regulate flow.
- The fluid is then directed through a cooler (typically a heat exchanger).
- The cooled fluid enters the seal chamber, providing lubrication and temperature control.
- The fluid then exits through the seal faces, maintaining a stable and clean environment for the seal.
Benefits
- Enhanced cooling – Reduces seal chamber temperature, preventing overheating and extending seal life.
- Better performance in high-temperature applications – Effective for processes where API Plan 11 would allow excessive heat build up.
- Prevents flashing – Cooling the fluid prevents it from vaporizing at the seal faces, which can cause dry-running and seal failure.
- Simple system with minimal maintenance – Requires only a cooler in addition to Plan 11’s setup.
Drawbacks
- Higher installation cost – Requires a cooler, adding complexity and expense compared to Plan 11.
- Increased maintenance – Coolers may require periodic cleaning or descaling, especially in hard water or dirty fluid applications.
- Not suitable for dirty or solid-laden fluids – Solids can clog the cooler and orifice, leading to system failure.
- Limited effectiveness if the cooler fails – If the cooling system is not maintained, it may lose efficiency, causing overheating.
Applications
- Oil & Gas Industry – Used in high-temperature hydrocarbon pumps where additional cooling is required.
- Petrochemical & Chemical Processing – Applied in pumps handling heated chemicals to prevent flashing.
- Power Generation – Common in boiler feedwater pumps to manage high operating temperatures.
- Refineries – Used in light hydrocarbon service pumps where process fluid cooling improves seal performance.
- General Industrial Pumps – Suitable for applications with elevated temperatures that could damage mechanical seals.
API Plan 21 is an improved version of Plan 11, designed for high-temperature applications where seal cooling is necessary. However, it requires a cooler and regular maintenance, making it more complex and costly than simpler flush plans.
Warning Notes
Related Technical Papers
Applicable Products
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