VENTING VERTICAL PUMPS V028
Vertical pump applications are very different than horizontal pump applications because the stuffing box is often the high liquid point in the system. Air becomes trapped in the stuffing box and cannot get out. In a majority of mechanical seal designs the seal faces and dynamic elastomer are often located in this trapped air pocket.
Since heat is a major destroyer of mechanical seal faces and elastomers, you will want to keep them submerged in fluid to help control any temperature rise.
Many cartridge seal designs have a flush port that can be connected to the suction side of the pump to remove this air. If this port is not available you may have to install a ported plate between the stuffing box face and the stationary part of the mechanical seal. Remember to connect a vent or suction recirculation line from this port to the suction side of the pump.
Try to picture this tandem seal in a vertical position and you will see that it is impossible to vent air through the stuffing box lantern ring connection, or the circulating connection between the seals.
In this seal design both the upper and lower seal faces and the dynamic elastomers would run dry unless you can figure out how to vent them. You might want to look at seal designs that put the faces and elastomers in a more favorable position.