Technical Foundation
What Is a Flow Switche?
A flow switch monitors liquid or gas flow in a pipe or duct and changes the state of an electrical contact when flow rises above or falls below a set trip point, most commonly used to protect a pump from running dry or to confirm flow is present in a cooling or process loop before allowing equipment to operate. Paddle-style switches use a vane or paddle inserted into the flow stream that deflects against a spring-loaded reed or micro-switch; shuttle/piston switches use a spring-opposed piston that moves with flow velocity to actuate a magnetic reed switch, offering a more repeatable and adjustable trip point than a simple paddle.
Thermal dispersion switches use a heated sensing element and measure the cooling effect of fluid flow past it, offering no moving parts (eliminating mechanical wear) and functioning down to very low flow rates that would not deflect a mechanical paddle. Switches are specified by pipe/duct size, wetted material compatibility with the fluid, and trip point (the flow rate at which the switch changes state), which for pump protection duty should be set comfortably above the pump's minimum safe flow rather than at the exact minimum.
Prefer a quick quote?
Get Flow Switches Pricing in Your Inbox
Skip the search — tell us the pipe size, fluid and desired flow trip point and we will come back with pricing.
| Spec | What It Means | Why It Matters |
|---|---|---|
| Sensing Technology | Paddle, shuttle/piston, thermal dispersion | Mechanical (paddle/shuttle) types are simpler and lower cost; thermal types have no moving parts and detect lower flow rates |
| Trip Point (Set Point) | Flow rate at which the switch changes state | Should be set with margin above the actual minimum safe flow, not at the exact threshold, to avoid nuisance trips |
| Pipe/Duct Size & Connection | NPT, flanged, or insertion/saddle mounting | Must match the process line size and available installation access (in-line vs. insertion into an existing pipe) |
| Wetted Material | Brass, stainless steel, PVC, depending on fluid | Must resist corrosion or degradation from the specific process fluid, especially in chemical or high-temp service |
| Switch Output | SPDT relay contact, or solid-state output | Must match the pump controller or safety circuit's input requirements for wiring compatibility |
Shop Flow Switches
Browse Flow Switches Sub-Categories
Organised by sensing technology. Pick a sub-category, or describe the pipe size and fluid and let ChatMRO match the switch.
How it works
From Half-Remembered Part Number to PO, in Three Steps.
Ask
Type an MPN, paste a spec sheet, or describe the part in plain English. ChatMRO understands engineer-speak.
Compare
Side-by-side specs, cross-references, and equivalents from multiple sources — without the clutter of endless browser tabs.
Quote & Buy
Request a quote or add to cart. Volume discounts, VAT-aware pricing, and consolidated procurement — all in one place.
Applications
Where Flow Switches Get Used
Flow switches are specified wherever equipment operation must be interlocked to the confirmed presence (or absence) of fluid flow.
Pump Protection
Shutting down or preventing start of a pump when suction or discharge flow drops below a safe minimum, preventing dry-run bearing and seal damage.
Cooling System Interlocks
Confirming cooling water flow is present before allowing welders, lasers, induction heaters or other heat-generating equipment to energize.
HVAC Chiller & Boiler Systems
Flow proving switches confirming adequate water flow through a chiller or boiler before allowing the heat source to fire, per safety code.
Process & Chemical Systems
Monitoring flow in reactor cooling jackets and process lines to trigger alarms or interlocks on loss of flow.
Fire Protection & Sprinkler Systems
Flow switches detecting water movement in a sprinkler system to signal alarm panels that a sprinkler has activated.
Compressed Air & Gas Systems
Air/gas flow switches confirming purge or cooling air flow in industrial equipment before allowing operation to proceed.
FAQ
Flow Switches Questions, Answered
What's the difference between a paddle flow switch and a shuttle-type flow switch?
A paddle switch uses a simple vane that deflects directly against a spring-loaded micro-switch when flow pushes on it, offering a fixed or coarsely adjustable trip point at relatively low cost. A shuttle (piston) switch uses a spring-opposed piston moving inside a flow-through body, actuating a sealed magnetic reed switch — this design typically offers a more precisely adjustable and repeatable trip point and better durability since the switching element isn't directly in the wetted flow path.
How do I set the trip point for pump dry-run protection?
Set the trip point comfortably above the pump manufacturer's stated minimum safe continuous flow, not right at that threshold — flow measurement has some variability, and setting the trip point too close to the actual minimum risks nuisance trips or, worse, insufficient margin if flow briefly dips below the switch's threshold before it reacts.
Why does my flow switch give false trips?
Common causes include turbulence from nearby elbows, valves or pump discharge too close to the switch (most manufacturers specify a minimum straight pipe run upstream and downstream), a trip point set too close to normal operating flow, or for paddle switches, debris or scale buildup affecting paddle movement. Thermal dispersion switches avoid the mechanical-wear causes but can be affected by fluid temperature changes if not properly compensated.
Can a flow switch measure exact flow rate?
No — a flow switch is a threshold device that indicates flow is above or below a set point, not a flow meter that measures and reports actual flow rate continuously. Applications needing a numeric flow reading require a flow meter (turbine, magnetic, ultrasonic, etc.) rather than a flow switch.
What wetted material should I choose for a flow switch?
Brass or bronze suits general water service; stainless steel is specified for corrosive fluids, higher temperatures, or sanitary/food applications; PVC or other plastics suit chemical compatibility in non-metallic piping systems. Match the wetted material to the actual process fluid's corrosivity and temperature, not just the pipe material it's installed in.
Keep browsing
Related Categories
Explore More
Find Your Next Part Now.
Describe a part number, spec or what it does.