The series PSM Flowmeters work according to the variable area principle, obtained by a float that moves along a tapered tube made of technical plastic materials.The force of the flow pushes the float to a certain height inside the tapered tube, to an equilibrium point.Each height or position of the float corresponds to a value of flow rate. Flow-Rate measurement of gases and clear liquids Size: 1/2″ and 3/4″; Clear Polysulfone Plastic Tube; PVC (standard), Polypropylene or Stainless Steel Connections Threaded Process Connections; Option: Adjustable Alarm - REED 250 Vac, 0.5 A, 12 VA (STANDARD)