API Plan 11
API Plan 11 – Discharge Recirculation to Seal Chamber
API Plan 11 is a commonly used flush plan where process fluid is taken from the pump discharge and recirculated back into the seal chamber through an orifice or flow control device. It helps to cool and lubricate the mechanical seal, preventing overheating and excessive wear.
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Features
How It Works:
- Fluid is drawn from the pump discharge (high-pressure region).
- It is passed through a flow control orifice to regulate flow and prevent excessive pressure drop.
- The process fluid enters the seal chamber, providing cooling and lubrication.
- The fluid then exits through the seal or leaks slightly into the pump, maintaining a clean environment.
Benefits
- Simple and cost-effective – No external fluid source required, reducing operational costs.
- Effective cooling and lubrication – Helps maintain optimal seal performance.
- Reduces solids accumulation – Flow from the discharge helps flush out any debris from the seal chamber.
- Common and widely used – Standard practice in many industries, making it easy to implement and maintain.
Drawbacks
- Not suitable for dirty or solid-laden fluids – Solids can cause wear and clog the orifice, leading to failure.
- Limited cooling capability – If the process fluid is already hot, it may not effectively cool the seal.
- Can cause flashing in high-temperature fluids – If the pumped fluid has a low boiling point, it may vaporize in the seal chamber.
- Pressure differential dependency – Requires sufficient pressure difference between the pump discharge and the seal chamber for proper flow.
Applications
Common Applications:
- Oil & Gas Industry – Used in pumps handling clean hydrocarbons, lubricating oils, and refined products.
- Petrochemical & Chemical Processing – Applied in pumps transferring chemicals that do not solidify or crystallize.
- Power Generation – Used in boiler feedwater and cooling water pumps to ensure seal longevity.
- Water & Wastewater Treatment – Commonly used in clean water and industrial water circulation pumps.
- Food & Beverage Industry – Suitable for clean fluid applications where external contamination must be avoided.
API Plan 11 is one of the most widely used mechanical seal flush plans due to its simplicity, cost-effectiveness, and efficiency. However, it is not recommended for applications with dirty, hot, or volatile fluids, as it may lead to clogging, inadequate cooling, or flashing.
Warning Notes
Related Technical Papers
Applicable Products
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