Plan 31S
API Plan 31 – Discharge Recirculation with a Cyclone Separator with Sample Pot
Plan 31S is equipment reliability innovative adaption of a conventional Plan 31 system.
API Plan 31 is a mechanical seal flush plan that recirculates process fluid from the pump discharge through a cyclone separator, which removes solids and particulates before directing the cleaned fluid into the seal chamber. The separated solids are returned to the pump suction, preventing them from reaching and damaging the mechanical seal. This plan is commonly used for pumps handling dirty or particulate-laden fluids where abrasion could shorten seal life.
However the Plan 31S system includes a sample collector which allows in-progress inspection of the process media entering the mechanical seal environment.
The Plan 31S system is designed to provide substantially clean fluid to the mechanical seal faces and the sample collector helps the engineer to condition monitor the performance of the system.
Instead of sealing a process fluid full of seal harming contaminants, the Plan 31S system provides clean fluid for cooling and lubrication of the mechanical seal.
Features
How API Plan31S Works:
- Process fluid is taken from the pump discharge and passed through a cyclone separator.
- The cyclone separator removes heavier particles and solids from the fluid via centrifugal force.
- Cleaned fluid enters the seal chamber, providing lubrication and cooling for the mechanical seal.
- The separated solids are redirected back to the pump suction, preventing them from entering the seal chamber.
- Integral Sample Collector Pot with ball valve.
Benefits
How API Plan 31S Works
- Extends seal life – Keeps abrasive particles away from the seal faces, reducing wear and maintenance.
- Improves seal performance – Provides cleaner fluid for lubrication and cooling.
- No external flush fluid needed – Uses process fluid, reducing operational costs.
- More effective than a basic strainer or filter – Continuous separation prevents clogging issues seen in API Plan 12.
- Simple, efficient elimination of solid particles
Drawbacks
- Limited effectiveness for very fine particles – Small solids may not be fully removed, potentially causing wear over time.
- Cyclone separator efficiency depends on process conditions – Effectiveness varies based on particle size, fluid velocity, and density differences.
- Not suitable for high-viscosity fluids – Thick fluids reduce separation efficiency, leading to inadequate filtration.
- Requires proper design and maintenance – Inefficient or worn separators may fail to protect the seal, leading to premature failure. Periodic cyclone separator checks to determine internal wear
Applications
API Plan 31 is a reliable flush plan for particulate-laden fluids, providing continuous solid separation to protect mechanical seals. However, its efficiency depends on process conditions, and it may not fully remove fine particles, requiring careful selection and maintenance.
- Used in process fluid applications containing suspended solids.
- Used in applications containing solids with specific gravity twice or more than that of process fluid.
Warning Notes
1. The Plan 31 cyclone separator ideally requires at least a 1.7 bar (25 psi) differential between pump discharge and the seal chamber for optimum performance.
2. A throat (restriction) bushing is recommended at the bottom of the seal chamber.
3. Cyclone separator must be periodically inspected for abrasive wear. If left unchecked, and wear reduces the seperator wall thickness, catasphoic failure can result.
3. The efficiency of a cyclone separator is proportional to it's diameter. A large cyclone diameter the less efficient the separation process.
4. The differential pressure between the inlet and outlet of the cyclone separator should be as close to zero as possible.
5. The maximum process fluid particle size should be less than 25% of the cyclone separator inlet orifice.
6. Avoid using Plan 31 on very dirty or slurry applications
Related Technical Papers
For further reading on API Plan 31 systems and seals, please click the following links to related Technical Blogs;
Applicable Products
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