API Plan 11

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API Plan 11 Flush Plan

API Plan 11

Overview:

  • API Plan 11 utilizes high pressure fluid from the discharge of the pump to provide cooling and lubrication for the mechanical seal.

Advantages:

  • Relatively low cost – only tubing or piping and a flow control orifice are needed.
  • Low maintenance – if a flow control orifice is installed: routine inspections to ensure that the orifice is not obstructed. This entails measuring temperature upstream and downstream of the orifice.

Best For:

  • Single mechanical seals
  • Clean process fluids – free of contaminants and abrasives
  • 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 11 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 11 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 flow control orifice. If the temperature downstream of the orifice is appreciably cooler, the 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.