Pump Seal Clarification

some needs priming, others cooling and sealing. It all depends on the process.

At times some engineers should step back and look at the over picture, instead of looking through a small spectrum.

This should help you.

A pump seal is to prevent the leakage of the water out from the water pump during the pump is running. It also help to prevent sucking air in to the water pump where it will cause your pump to be inefficiency. This caused pressure loss, flow loss and wastage of energy. The pump seal also help to prevent of water leak into your motor if you have a direct couple pump like single stage pump.

Pump seal will never heat up your pump shaft unless if it is damage or if you install a wrong pump seal to it.

The purpose of a pump seal is to prevent leakage either out of the pump (positive pressure at location of seal) or into the pump due to low or negative pressure (i.e. double inlet-between bearing design). The purpose of the pump seal fluid is to lubricate and cool the pump seal when the pump is running or to prevent air leakage into the system if the pump is idle.

A second very important purpose is to provide CLEAN fluid to the seal i.e. pumping sewage, provide a clean source of water to the seal so a clean water buffer would exist and a slight stream into the pump keeps contaminants away from the seal. In cases of a heavy oil or a hot oil a separate source of cooler lighter weight oil would be used between the seal and the pumped fluid.

Often it is sufficient to use the actual pumped fluid as a clean fluid by running it through either a small cyclone filter or a Y strainer, reducing the pressure by means of an orifice and cooling it by some means to an acceptable temperature.

The materials used in a seal and even its design are predicated on the temperature of the fluid, the RPM of the pump, the corrosiveness of the fluid and the pressure at the stuffingbox area. These are very important parameters in the selection of the seal or its components material. The fluid temperature and its physical/chemical make-up determine the seal flushing medium requirements.

In regard to the answers you got, it would be a stretch to say that it is only for the either the bearings or the start-up. Pumps using cleaned filtered discharge do not usually have a separate source of fluid. The springs provided in the seal should be sufficient to seal during the idle period since the maximum differential can only be 14.7 psi at that time. As to the bearings - don't really think so. A cooling coil in the bearing housing would do that. As aforementioned, keeping the seal cool yes, keeping the shaft cool- no. However, if there was packing in the stuffing box instead of a seal then there would be cooling of the shaft and it would be necessary as well as providing lubrication between the packing and the shaft to prevent excessive wear.