PISTON TYPE Viscosity Compensating Switches Contents Page Start FS-4 Series Molded Plastic Construction ..................... G-6 O-RING FS-150 Series Straight-Through Flow Path, Ryton Material ................................................... G-7 Partial Cutaway (FS-930 Series) VISCOSITY COMPENSATING PISTON FS-380 Series High Pressure Inline ....................................... G-8 When temperatures of viscous fluids change, so do their flow properties. With viscosity lowered by increasing temperature, a greater flow is generally required to create actuation pressure differential. A unique patented piston within GEMS FS-930 Series switches accommodates these changes in fluid viscosity while maintaining accurate switch actuation. Units can detect flow rates with 20% accuracy for liquid viscosities between 40 to 1000 SSU. FS-380P Series Inline - Plastic Flow ........................................ G-9 FS-480 Series Low Pressure Drop........................................ G-10 Low Pressure Drop Switches FS-927 Series Miniature Brass Switches .......................... G-11 ENCAPSULATED REED SWITCH FS-925 Series General Purpose ............................................. G-12 OVER-MOLDED PISTON WITH MAGNET FS-10798 Series Externally Adjustable .................................. G-14 METERING DISC O-RING FLOW SWITCHES SPRING FS-926 Series Low Flow ............................................................ G-12 FS-930 Series Viscosity Compensating............................. G-16 The key to the excellent flow qualities of the FS-150 and FS-380 Series switches is the dual diameter internal bore. At flow rates below the actuation point, the fluid passes around the piston and metering disc within the " metering bore. " As fluid flow increases past the actuation point, the metering disc enters the " flow bypass bore " where the increased diameter provides generous flow paths. The result is a low pressure drop for high flow rates and less susceptibility to fouling. Typical Piston and Spring Removal PISTON PISTON SPRING INLET FITTING PLUG O-RING SPRING Accumulation of foreign debris should periodically be removed from these switches. GEMS' designs provide for easy piston and spring removal for this occasional cleaning. Recommended cleaning procedures are provided in the Instruction Bulletin shipped with each unit. 150 micron filtration is recommended for the FS-150 Series; 100 micron for FS-380, 50 micron filtration is recommended for all other piston type switches. NOTE: All air/gas Flow Switches are factory calibrated using a special piston. Water calibrated units are not recommended for air/gas applications. Piston Intro / p2of2 / 28-APR-14 Visit www.GemsSensors.com for most current information. G-5http://www.GemsSensors.com