Pressure switches are more reliable on slurries than pressure relief valves and easier to reset than rupture disks. Several manufacturers offer control boxes to interface with the pressure switch and isolator ring assembly. These boxes incorporate local push-button control stations and include a timer to enable the pump to prime itself each operating cycle. Some of these boxes incorporate seal flush controls as well. To use this approach, it is necessary to understand the difference between static pressure, friction pressure and total pressure.
Static head is the pressure resulting from the weight of the liquid in the pipe.
Static pressure results from the pipe being filled with liquid and is present even when the pump is idle. It is not influenced by pipe size, number of fittings or viscosity. Static pressure is determined solely by fluid density and the difference in height between the pressure switch and the outlet of the pipe. 12 ft above the gauge, so static head is 12 ft, which exerts 5 psi of pressure. Friction pressure results from the flow of liquid through a pipe and is present only when the pump is running.