API Plan 12

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API Plan 12 Seal Flush Plan

API Plan 12

Overview:

  • API Plan 12 utilizes high pressure fluid from the discharge of the pump to provide cooling and lubrication for the mechanical seal. The pumped fluid is routed through a y-strainer and flow control orifice before being injected into the mechanical seal.
  • The y-strainer is included in this piping plan to remove occasional large particles.

Advantages:

  • Relatively low cost – only tubing or piping, y-strainer, and flow control orifice are needed.

Disadvantages:

  • Y-Strainer is susceptible to clogging and can potentially restrict or obstruct fluid flow to the seal. Routine maintenance is needed to clean the y-strainer.
  • The long term reliability of this piping plan has not been proven.

Best For:

  • Single mechanical seals
  • Clean process fluids – free of contaminants and abrasives. Occasionally subject to large particles.
  • Process fluids not susceptible to polymerization or “setting-up” at ambient or lower temperatures

Best Practices:

  • Orifice size should be no less than 1/8 in. (0.125 in.)
  • Calculate the pressure differential between the pump discharge pressure and the seal chamber pressure to ensure positive flow into the seal.
  • Isolation valves should not be installed in the Plan 12 flush piping. If such a valve is installed in the flush line, there poses the risk of it being closed and preventing flow to the seal. In such an event, the seal life will be drastically reduced and subsequently fail due to the lack of cooling and lubrication.
  • Routine Maintenance
    • Check the piping or tubing temperature against that of the pump. If the Plan 12 flush piping is appreciably cooler than the pump temperature, there may be an obstruction in the flush piping.
    • Additionally, check the temperature both upstream and downstream of the y-strainer and flow control orifice. If the temperature downstream of is appreciably cooler, the y-strainer or orifice may be obstructed. Immediate action is needed to clear the obstruction. If found obstructed, the seal is likely damaged and needs to be replaced.
    • Alternatively, measure the differential pressure across the y-strainer and flow control orifice to determine if they are obstructed.