US Patent 7938018 Liquid flow sensing systems

A liquid flow sensing system for sensing the flow of liquid within a supply line (2) of a metering pumping machine, the system including a magnetic member (4) arranged for movement relative to a pneumatic switch (8) operated by the presence or absence of a magnetic field, the magnetic member (4) being contained within a sealed unit (5) located within the supply line (2) and the arrangement being such that, when the liquid flow rate falls below a predetermined level, the magnetic member (4) moves downwardly from a first operative position into a second operative position.