Normally pump protection valves are limited to minimum flow protection; however, severe damage can occur to the pump and driver by exceeding the intended operating range of the pump.
Damage due to excessive flow can be eliminated by designing a “Maxi-Flow” as an addition to the standard minimum flow valve.
Excessive flow protection is achieved by installing an insert with a row of orifice holes into the main valve body. During normal main flow operation, the fluid passes through the holes with a minimal pressure head loss. In addition, a special disc is provided which has a sleeve around the diameter with a row of orifice holes.
The disc is at full lift when the forward flow reaches the maximum desired flow rate. At the full lift, the orifice holes in the body insert and disc line up stopping the additional flow.
Maximum flow protection prevents exceeding the steam drum desired water level if the drum level control valve failed open in boiler feed service. For process fluids and seawater in which pipe corrosion is a concern, the maximum flow protection provides run out protection if piping leaks occur from corrosion.