nature of a gas or liquid contained in a pipeline. TheModel 633 can provide multiple contact closuressignifying the kind of fluid in the pipeline. The 633 isused instead of target type flow switches when flowdetection does not provide a complete or reliableanswer.A simple application is to protect pumps against runningwith a dry suction. The sensor is inserted into the pumpsuction line; a contact closure is produced when there isno fluid present. This prevents seizing, galling, orburned seals in a dry pump.The Model 633 fluid switch can be used to detect lossof liquid flow in a pipeline where the flow does notactually stop. An example of this situation can be foundwhere an air pressure tank pad instead of a pump isused to move the liquid. The flow of the liquid and not ofthe air is the variable of interest. A target type switch isnot reliable in this application because the pad air willcontinue to flow after the liquid supply has beenexhausted. The target switch will be kept activated bythe air flow. It cannot distinguish between liquid andhigh air flow. The Model 633 can tell the difference andwill produce a reliable alarm signal.The Delta Controls Model 633 can also detect thechange in composition of the fluid. A good commonapplication is decanting a process liquid after a waterwash. The change in the flowing liquid from water toproduct is detected and an output contact is produced.