Is the pressure of the mechanical seal water in a centrifugal pump higher than the outlet pressure or the inlet pressure?

It is generally higher than the inlet pressure; the exact value depends on the pump’s design. If the mechanical seal is located on the water inlet side of the impeller (as in some double-suction pumps), or if there are balance holes in the impeller, or if the sealing chamber is connected to the inlet, then it is usually sufficient for the pressure to be higher than that at the pump’s inlet. It is best to consult the pump manufacturer for confirmation

There are many schemes for flushing and cooling mechanical seals; common methods of flushing and cooling include self-flushing, where the flushing fluid is introduced into the seal chamber from the pump’s outlet end through a pipe. Backwashing: The flushing medium is introduced into the sealing chamber through a pipe at the inlet end of the pump for backwashing. Through-flushing: A structure that combines self-flushing and back-flushing is called through-flushing. External flushing involves introducing a pressurized medium from the external system into the sealed chamber; however, the flushing medium is either the same as the medium inside the sealed chamber or a medium that has no impact on the production process. Moreover, the machine seal flushing scheme refers to flushing fluids (water, oil, medium, etc.), not just water. According to \"Modern Pump Theory and Design,\" the flushing fluid pressure should be higher than the pressure in the sealing chamber (the medium), which can be understood as the outlet pressure. The specific solution to be adopted needs to be selected based on factors such as the on-site operating conditions, process requirements, pressure, and temperature. Only after selecting a flushing scheme can other conditions such as the flow rate, pressure, and temperature of the flushing fluid be determined. It is recommended to take a look at the introduction to the mechanical seal auxiliary system in API682