Flow Switches & Sensors

FS-550 Series Flow Switch

Part Number: 56730
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FS-550 Series Flow Switches sense liquid flow in either direction to monitor flow/no-flow conditions and are supplied in two paddle lengths. The paddle is trimmed during installation to permit switch actuation at the desired flow rate. As flow increases, the paddle of the switch pivots to move out of the liquid path, producing less than 3 psig (.21 bar) of pressure drop regardless of pipe size. Applications include: compressors, heat exchangers, turbines, engines, boilers, chillers, valves, pumps and regulators.


5 days
Lead-times and expedites

Lead-times apply to standard parts & configurations. Expedited shipments available by contacting factory. Lead-times may vary based on quantity and/or non-standard configurations.

CE ROHS Gems Compliant CSA


  • Engineered for Positive Liquid Flow Detection at Pressures to 2000 psig (137.9 bar)
  • Unique; Patented Cam Design Assures Low Pressure Drop and Does not Require Bellows; Seals; or Mechanical Linkages
  • Minimum In-Line Restriction; Paddle Pivots to Move Out of Liquid Path with Increasing Flow
  • Pipe Line Size: 1 1/4" and up
  • Primary Construction Material: Stainless Steel or Brass
  • Setting Type: Fixed
Sensor Type
Paddle Type
Primary Material Of Construction
Body Material
Wetted Materials
Brass, 316 Stainless Steel, Teflon®, Ceramic
Minimum Pressure
Over 500 psi
Maximum Pressure
2,000 psi
Minimum Temperature
Maximum Temperature
Flow Setting
15.0 - 52.0 GPM
Flow Setting Range
Adjustable Range
Set Point Accuracy
Set Point Differential
Switch Type
SPDT (20 VA)
Port Size
1" NPT Male
Electrical Termination
3-Pin Junction Box
Recommended Filtration
UL Recognized, CSA, CE, FM

Reed Switch Protection

Format .pdf
Size 56 KB

Gems Sensors Instructions, FS-550

Format .pdf
Size 887 KB

Gems Sensors Catalog, FS-550

Format .pdf
Size 2 MB
  • General Industry
  • General Industry - Fire Suppression
  • General Industry - Other
  • Marine - Commercial - Cruise Ships
  • Marine - Commercial - Other
  • Marine - Commercial - Ship Owner
  • Marine - Commercial - Workboats
  • Marine - Commercial - Yachts
  • Marine - Govt & Military - Military
  • Marine Vessels
  • Off Highway Vehicles
  • OHV - Fire Trucks
  • OHV - Military Vehicles
  • OHV - Mining Equipment
  • OHV - Refueling Trucks
  • OHV - Specialty Equipment
  • Process Applications
  • Process Industry - Other
  • Specialty Vehicles
Can a flow switch handle more flow than the flow set point?

A flow switch can typically handle a greater flow rate than its flow setting. Many flow switches are set 4 times less than the actual operating flow rate. As flow rate increases, pressure drop also increases, eventually causing a restriction of flow.

Can a flow switch be mounted at an angle?

Yes, piston and shuttle type switches utilizes a small, strong spring, that is not bothered by the mounting attitude of the flow switch and will perform at any orientation. The exception is our FS-400P, which is spring less.

Can a flow switch be cleaned?

Yes. The design facilitates cleaning by flushing out the flow switch with clean water. Some flow switches have removable parts for a more thorough cleaning.

If I add a small diameter connector to my flow switch, will it affect the pressure drop?

The pressure drop across the flow switch will not increase but you could see a pressure drop across the connector itself. Every flow fitting has a pressure drop associated with it.

Why is filtration necessary?

Filtration helps prevent clogging from solid particles. It is recommended but many applications do not use them. Certain flow switches are more susceptible to particles than others. A general rule to follow is the lower the set point the more susceptible to particles the unit becomes.

What is the difference between a flow switch and a flow sensor?

A flow switch detects the presence of the flow at a predetermined set point. A flow sensor is used for monitoring flow rate, telling the user the flow rate (i.e. 5 GPM).

Can flow switches be used for liquid or gas?

Yes, Gems has flow switches for liquid and gas applications. A flow switch intended for liquid flow should not be used on gas flow.

Can flow rate monitors be used for liquid or gas?

Gems flow sensors are limited to liquid flow rates. There are flow sensors available for gas measurement from other manufacturers.

Are flow switches set on the rise or the fall?

Typically, catalog units are set on the rise. Rising set points are most commonly used in coolant loops to insure proper flow. Switches can be calibrated on the fall when required.

What does SPST or SPDT switch mean?

SPST (single pole single throw) switch comes wired only one way, either normally open or normally closed. This is the best choice for OEM applications. It insures that it can only be wired one way. SPDT (single pole double throw) switch comes wired for both normally open and normally closed. Customers like this option when prototyping and unsure of the end requirement.

What is the minimum pressure needed to operate a flow switch?

Gems will list minimum pressure requirement, this is a very conservative specification, one that is application specific. If you have been using a unit below specification without issue, it is fine to continue its use. If you have flow through the unit then you have overcome all pressure drops in your system, including the flow switches.

Does viscosity make a difference?

Yes, as viscosity increases the set points come down. Check the specifications for your flow switch for recommended maximum viscosity.