Built tough for the most arduous industrial and mining applications. Rugged but highly-sensitive paddle switch with a billet-aluminium housing and a one-piece 316 stainless steel process connection. 400 bar pressure rating, manual override built into all models.
FM Series
Paddle Flow Switches
Features
- 5–500 V AC, 15 A S.P.D.T. switch (H model)
- Low-voltage gold-contact ‘L’ model available (FM-L)
- One-piece 316 stainless steel process connection
- Super-tough billet aluminium housing
- Manual override built in
- 3/4″ and 1″ models available with BSP or NPT threads
- 400 bar (5800 psi) pressure rating
- Seal-less magnetic drive
- Dieseline & high-temperature versions available
- Weatherproof IP67 housing
- Easily serviceable
The FM Series uses the same magnetic-coupling drive as the F Series — paddle motion is coupled to the high-compliance switch through a solid wall of stainless steel and aluminium, giving a high-pressure switch with no seals, diaphragms, bellows or other points of potential failure. Supplied as standard with a one-piece 316 stainless steel process connection and a fully machined billet aluminium housing. Available with a glass-fibre-reinforced polypropylene paddle, or a nickel copper alloy paddle for Dieseline and high-temperature applications. The paddle can be cut and shaped to suit pipework 25 mm (1″) or larger, and the built-in manual override switches the flow switch on at the press of a button regardless of flow. Suitable for use in bore water, sea water and many chemical solutions.
Trade customers should contact sales@kelco.co.nz for account pricing.
Ordering — Available Models
| Model Number | Description |
|---|---|
| FM-H-20B | Standard heavy-duty switch (H) — 3/4" BSP thread, polypropylene paddle for water use |
| FM-H-20B-D | Standard heavy-duty switch (H) — 3/4" BSP thread, nickel copper alloy paddle for Dieseline and high-temperature applications |
| FM-H-20N | Standard heavy-duty switch (H) — 3/4" NPT thread, polypropylene paddle for water use |
| FM-H-20N-D | Standard heavy-duty switch (H) — 3/4" NPT thread, nickel copper alloy paddle for Dieseline and high-temperature applications |
| FM-H-25B | Standard heavy-duty switch (H) — 1" BSP thread, polypropylene paddle for water use |
| FM-H-25B-D | Standard heavy-duty switch (H) — 1" BSP thread, nickel copper alloy paddle for Dieseline and high-temperature applications |
| FM-H-25N | Standard heavy-duty switch (H) — 1" NPT thread, polypropylene paddle for water use |
| FM-H-25N-D | Standard heavy-duty switch (H) — 1" NPT thread, nickel copper alloy paddle for Dieseline and high-temperature applications |
| FM-L-20B | Low-voltage gold-contact model (L) — 3/4" BSP thread, polypropylene paddle for water use |
| FM-L-20B-D | Low-voltage gold-contact model (L) — 3/4" BSP thread, nickel copper alloy paddle for Dieseline and high-temperature applications |
| FM-L-20N | Low-voltage gold-contact model (L) — 3/4" NPT thread, polypropylene paddle for water use |
| FM-L-20N-D | Low-voltage gold-contact model (L) — 3/4" NPT thread, nickel copper alloy paddle for Dieseline and high-temperature applications |
| FM-L-25B | Low-voltage gold-contact model (L) — 1" BSP thread, polypropylene paddle for water use |
| FM-L-25B-D | Low-voltage gold-contact model (L) — 1" BSP thread, nickel copper alloy paddle for Dieseline and high-temperature applications |
| FM-L-25N | Low-voltage gold-contact model (L) — 1" NPT thread, polypropylene paddle for water use |
| FM-L-25N-D | Low-voltage gold-contact model (L) — 1" NPT thread, nickel copper alloy paddle for Dieseline and high-temperature applications |
Operating Limitations
| Maximum operating pressure (FM with polypropylene paddle, ambient) | 400 bar / 5800 psi |
|---|---|
| Maximum operating pressure (FM-D with metal paddle, ambient) | 400 bar / 5800 psi |
| Minimum burst pressure (both models) | 800 bar / 11 600 psi |
| Maximum operating temperature (polypropylene paddle) | 80 °C / 176 °F |
| Maximum operating temperature (metal paddle, FM-D) | 100 °C / 212 °F |
| Minimum operating temperature (both models) | -60 °C / -76 °F |
| Ingress protection rating | IP67 |
Electrical Data
| Switch type | S.P.D.T. (single pole, double throw) standard heavy-duty microswitch for general control circuits up to 500 V AC — ideal for pump starters, relay logic, contactors and timers |
|---|---|
| Voltage range | 5 to 500 V AC (minimum load 160 mA at 5 V DC) |
| Maximum switched current | 15 A (10 A at 500 V AC). Maximum voltage and maximum current cannot be applied together. |
| Resistive or inductive load (125 V AC or 250 V AC) | 15 A |
| Resistive / inductive load at other voltages | 500 V AC: 10 A / 6 A; 8 V DC: 15 A / 15 A; 14 V DC: 15 A / 10 A; 30 V DC: 6 A / 5 A; 125 V DC: 0.5 A / 0.05 A; 250 V DC: 0.25 A / 0.03 A |
| Lamp load (NC / NO) | 3 A / 1.5 A at 125 V AC; 2.5 A / 1.25 A at 250 V AC; 1.5 A / 0.75 A at 500 V AC; 3 A / 1.5 A at 8, 14 and 30 V DC; 0.5 A / 0.5 A at 125 V DC; 0.25 A / 0.25 A at 250 V DC |
| Motor load (NC / NO) | 5 A / 2.5 A at 125 V AC; 3 A / 1.5 A at 250 V AC; 1.5 A / 0.75 A at 500 V AC; 5 A / 2.5 A at 8, 14 and 30 V DC; 0.05 A / 0.05 A at 125 V DC; 0.03 A / 0.03 A at 250 V DC |
| Direct motor control | Directly switches pump motors up to 1/4 HP (approx. 185 W) at 240 V AC. For larger motors use a contactor or relay. |
| FM-L switch type | Gold contact microswitch, S.P.D.T., gold alloy contacts, so it switches reliably at the low wetting currents of PLC inputs, telemetry and relay logic. Not suitable for inductive or capacitive loads such as contactors and relays. Loads above the rating will damage the switch. |
| FM-L rated current (resistive) | 0.1 A at 125 VAC; 0.1 A at 8, 14 and 30 VDC |
| FM-L inrush current | 0.1 A maximum (NC and NO) |
| FM-L minimum applicable load | 1 mA at 5 VDC |
| FM-L operating range (micro load) | 5 to 30 V, 5 to 800 mW (26 mA maximum at 30 V) |
| FM-L contact resistance | 50 mΩ maximum (initial) |
| FM-L typical applications | PLC, telemetry and low voltage control |
Dimensions
Manual Override
All FM models include a red manual override button on the side of the housing, under the cable gland. Pressing it switches the flow switch on regardless of flow — useful for manually starting pumps in spite of an initial lack of flow, and for testing/commissioning of control circuits. After wiring, press it to test: the switch changes state as if liquid were pushing the paddle.
Flow Sensitivity & Paddle Trimming
Cut the paddle to suit the application — it must clear the pipe wall by at least 4 mm all round. Use a hacksaw or tin snips (heavy-duty tin snips for the FM-D metal paddle). As a guide: low flow — paddle just clears the bottom of the pipe; unknown flow — 3/4 of the way across the pipe; high flow — 1/4 to 1/2 of the way across the pipe. Spare paddles are available if too much is cut off. The flow rates required to actuate depend on turbulence, viscosity, and the exposed paddle area. Use the online Paddle Calculator to estimate activation flow and determine the right cut.
Sensitivity Adjustment
FM switches are supplied at maximum sensitivity (adjuster wound fully in). To decrease sensitivity, remove the red dust cap and wind the adjusting screw out (anticlockwise) with a wide flat screwdriver. The further out the screw, the more flow is needed to operate the switch. Refit the dust cap.
Dieseline / High-Temperature Variant
Order the -D suffix (e.g. FM-H-25B-D) for dieseline service or operation up to 100 °C. The polypropylene paddle is replaced with a Nickel Copper alloy paddle. Kelco products are not intended for use in hydrocarbons other than dieseline.
Mounting
The switch can go in suction or delivery pipework, horizontal or vertical. In vertical pipework the flow must be upward, not downward. Never install the switch on the underside of horizontal pipework. Where possible, mount the switch away from pumps, valves and bends — a fitting directly upstream makes the flow uneven and turbulent at the paddle, which can shift the switching point slightly or make the paddle flutter near the switching point; downstream fittings have little effect. Mount in a pipe tee, tapping saddle or weld-on socket, square to the flow so liquid hits the flat face of the paddle, with the arrow on the switch pointing in the direction of flow. Seal the thread with PTFE tape or thread sealant, leaving at least 4 mm of thread above the socket, and tighten with a spanner on the spanner flats only — never twist the switch body.
Electrical Installation
The FM Series is a mains voltage device — all electrical work must be carried out by a licensed electrician. Terminals are marked C (common), NO (normally open) and NC (normally closed); for a two-wire connection use C plus either NO or NC to suit the application. Connect the earth terminal inside the housing: the FM must be earthed when operated at mains voltage. After wiring, fully tighten the cable gland nut, check the lid gasket is in place and tighten the lid down. Without its lid the switch is not water, weather or insect proof and presents a shock hazard.
Hazardous Areas
The FM-H is not certified for use in hazardous areas and must not be installed in any area classified as hazardous under AS/NZS 60079.10 (Zone 0, 1, 2, 20, 21 or 22). The FM-L is simple apparatus under AS/NZS 60079.11 and may be used in a hazardous area only as part of an intrinsically safe circuit, connected through suitably certified associated apparatus. It is not Ex certified in its own right. The associated apparatus must not exceed Uo ≤ 30 V, Io ≤ 100 mA. The full conditions of use are given in the installation sheet.
FM-L — Inductive and Capacitive Loads NOT Suitable
The FM-L is not suitable for inductive or capacitive loads such as contactors and relays. Loads above the rating will damage the switch.
Replacing the Paddle
The paddle and its associated pivot bearings are replaceable items. Spare paddles can be obtained from your supplier — please quote the part number of the flow switch when ordering. Replacement paddles are supplied with new bearing shells and a large retaining O-ring. On FM-D models the nickel copper alloy paddle, main arm and bronze pivot bearing are also replaceable; never undo or remove the sealed hexagonal cap at the top of the main arm, which houses the magnet.
Materials & Chemical Compatibility
All FM models have a one-piece 316 stainless steel process connection and a billet aluminium housing. The standard FM has a glass-fibre-reinforced polypropylene paddle for water use; the FM-D has a nickel copper alloy paddle. Suitable for use in bore water, sea water and many chemical solutions. Check that the switch materials suit the liquid being monitored.
Approved Standards
The ‘H’ and ‘L’ microswitches used in the FM Series are approved to UL1054 (File E41515), CSA C22.2 No.55 (File LR21642) and EN61058-1, and are CE marked.
Serviceability
Fully field-serviceable. The paddle and its pivot bearings are replaceable items (on the FM-D, the nickel copper alloy paddle, main arm and bronze pivot bearing). The electrical housing is a separate assembly that locks onto the wet-end with a single externally-accessible screw — swap modules without disturbing pipework. Replacement paddles, seals and switches available from Kelco Engineering or your distributor.
