The purpose of a mechanical seal flush piping is to lubricate and cool the pump's mechanical seal. One of the most commonly used type of mechanical seal flush piping is the API Plan 11 or Plan 13. Although these piping plans are intended for API pumps, the same piping plans are widely used in other pumps because they are simple and inexpensive.
API Plan 11
This API seal flush piping plan is used in single seal or in the primary seal of unpressurized dual seals. The seal flush comes off the pump discharge nozzle through a flow control orifice to the seal. The flow enters the stuffing box (seal chamber), flushes the seal faces and through the sea, and is recirculated back to the pump suction. This seal plan is for use in horizontal pumps and is not recommended for vertical pumps.
A Plan 11 is to be used in a pump whose impeller has back wear rings. The pressure on the back side of the impeller at the balance holes pitch circle is nearly equal to suction pressure. Thus there is adequate pressure to circulate the flush liquid from the seal chamber to the pump suction.
API Plan 13
This API seal flush piping plan is used in single seal or the primary seal of unpressurized dual seals. The seal flush comes off the throat, or throttle, bushing and through the stuffing box (seal chamber). The flow flushes the seal and is recirculated through a flow control orifice back to the pump suction. This seal plan is suitable for both horizontal and vertical pumps.
A Plan 13 is to be used in a pump whose impeller has no back wear rings which is typical in end-suction pump in high suction pressure service where the impeller back wear ring is omitted to balance the hydraulic axial thrust load. The pressure behind the impeller adjacent to the stuffing box is higher than suction pressure so there is enough pressure differential to circulate the flush liquid back to the pump suction. In an impeller with balance holes there may not be enough differential pressure to circulate the flush liquid through the stuffing box and back to the pump suction.
The required differential pressure is typically [ * ] PSIG to [ * ] PSIG. The required seal flush flow ranges from [ * ] GPM to [ * ] GPM depending on the mechanical seal size and its rotational speed. Consult the seal vendor for recommendation.
[ * ] Some information are excluded in this article. Read more.