Siemens QVE1901U FLOW SWITCH, SPST, 1A, 3/4" TO 8" PIPE DIAMETERSSiemens QVE1901U Flow Switch, SPST, 1A, 3 4" To 8" Pipe Diameters Flow switches are used to monitor the flow of fluids in hydraulic systems, especially in refrigeration and heat pumps, and are for use with condensers, boilers, and heat exchangers. Detects the flow of the medium to be monitored by means of a paddle. If the flow velocity in the piping falls below the adjusted switch off value, a switch with a dry contact (S. P. D. T.), closes the