Uses a flexible stainless wire sensor rather than a paddle to detect flow. Suits open discharge applications and pipes from 50 mm (2″) upwards. Ideal where solids or semi-solids are present — sewage pumping, slurry, mining, and high-velocity normal pumping where paddles foul or fatigue.
TW Series
Trailing Wire Flow Switches
Features
- Unique trailing-wire sensor (no paddle to foul)
- 5 to 500 V AC, 15 A S.P.D.T. switch standard (TW-H)
- Low-voltage gold-contact model available (TW-L)
- 1″ BSP or NPT models available
- 316 stainless or polypropylene models
- Trailing wire lengths from 50 to 300 mm (2″ to 12″)
- Easily serviceable
- 400 bar / 5800 psi rated models available (stainless)
- Manual override built into all models
- Seal-less magnetic drive
- Adjustable sensitivity
- IP67 weatherproof
The trailing-wire sensor flexes with the flow rather than fighting it, so it tolerates entrained solids, fibres and high velocities that would damage a paddle. The flexible stainless wire sensor offers major advantages over conventional paddles where solids or semi-solids are present, such as in sewage pumping, and is also suitable for slurry and mining applications and many normal pumping situations where the flow velocity is high and paddle-type switches are unsuitable. Supplied with a polypropylene or 316 stainless steel process connection in 1″ BSP or NPT. The standard TW-H model uses an S.P.D.T. micro-switch rated 5 to 500 V AC, 15 A; the TW-L low-voltage model uses an S.P.D.T. gold-contact micro-switch for low wetting current signalling such as PLC inputs and telemetry. The earlier TW-RL reed-switch models are being phased out and replaced by the TW-L. A manual override is built into all TW Series models.
Trade customers should contact sales@kelco.co.nz for account pricing.
Ordering — Available Models
| Model Number | Description |
|---|---|
| TW-H-25B-50 … TW-H-25B-300 | Standard SPDT, 1″ BSP, all polypropylene wetted parts |
| TW-H-25N-50 … TW-H-25N-300 | Standard SPDT, 1″ NPT, all polypropylene wetted parts |
| TW-H-25B-SS-50 … TW-H-25B-SS-300 | Standard SPDT, 1″ BSP, 316 stainless process connection (high-pressure model) |
| TW-H-25N-SS-50 … TW-H-25N-SS-300 | Standard SPDT, 1″ NPT, 316 stainless process connection |
| TW-RL-25B-50 … TW-RL-25B-300 | Low-voltage gold-contact reed switch, 1″ BSP, all polypropylene |
| TW-RL-25N-50 … TW-RL-25N-300 | Low-voltage gold-contact reed switch, 1″ NPT, all polypropylene |
| TW-RL-25B-SS-50 … TW-RL-25B-SS-300 | Low-voltage gold-contact reed switch, 1″ BSP, 316 stainless process connection |
| TW-RL-25N-SS-50 … TW-RL-25N-SS-300 | Low-voltage gold-contact reed switch, 1″ NPT, 316 stainless process connection |
| TW-L-25B-50 … TW-L-25B-300 | Low-voltage gold-contact model (L) — S.P.D.T. gold-contact micro-switch, 1″ BSP, all polypropylene wetted parts |
| TW-L-25N-50 … TW-L-25N-300 | Low-voltage gold-contact model (L) — S.P.D.T. gold-contact micro-switch, 1″ NPT, all polypropylene wetted parts |
| TW-L-25B-SS-50 … TW-L-25B-SS-300 | Low-voltage gold-contact model (L) — S.P.D.T. gold-contact micro-switch, 1″ BSP, 316 stainless process connection (high-pressure model) |
| TW-L-25N-SS-50 … TW-L-25N-SS-300 | Low-voltage gold-contact model (L) — S.P.D.T. gold-contact micro-switch, 1″ NPT, 316 stainless process connection |
Operating Limitations
| Maximum operating pressure (all-polypropylene model, static or dynamic, ambient) | 18 bar / 261 psi |
|---|---|
| Pressure de-rating (all-polypropylene model) | Maximum operating pressure must be de-rated linearly as operating temperature increases, so that at 60 °C / 140 °F it does not exceed 1 bar / 15 psi absolute |
| Maximum operating pressure (stainless model, static or dynamic, ambient) | 400 bar / 5800 psi |
| Minimum burst pressure (all-polypropylene model, ambient) | 45 bar / 652 psi |
| Minimum burst pressure (stainless model, ambient) | 500 bar / 7215 psi |
| Maximum operating temperature (polypropylene) | 60 °C / 140 °F (see pressure de-rating) |
| Maximum operating temperature (stainless) | 80 °C / 176 °F |
| Minimum operating temperature | -20 °C / -4 °F |
| Ingress protection rating | IP67 |
Electrical Data
| TW-H switch type | S.P.D.T. (single pole, double throw) microswitch for general control circuits from 5 to 500 V AC — ideal for pump starters, relay logic, contactors and timers. Minimum load 160 mA at 5 V DC. |
|---|---|
| TW-H direct motor control | Directly switches pump motors up to ¼ HP (approx. 185 W) at 240 V AC. For larger motors use a contactor or relay. |
| TW-H absolute limits | 500 V AC and 15 A maximum (10 A at 500 V AC); 5 V DC and 160 mA minimum. Maximum voltage and maximum current cannot be applied together — use the load ratings below for the limit at each voltage and load type. |
| TW-H load ratings at 125 V AC | Resistive 15 A (NC/NO) · Lamp 3 A (NC), 1.5 A (NO) · Inductive 15 A (NC/NO) · Motor 5 A (NC), 2.5 A (NO) |
| TW-H load ratings at 250 V AC | Resistive 15 A (NC/NO) · Lamp 2.5 A (NC), 1.25 A (NO) · Inductive 15 A (NC/NO) · Motor 3 A (NC), 1.5 A (NO) |
| TW-H load ratings at 500 V AC | Resistive 10 A (NC/NO) · Lamp 1.5 A (NC), 0.75 A (NO) · Inductive 6 A (NC/NO) · Motor 1.5 A (NC), 0.75 A (NO) |
| TW-H load ratings at 8 V DC | Resistive 15 A (NC/NO) · Lamp 3 A (NC), 1.5 A (NO) · Inductive 15 A (NC/NO) · Motor 5 A (NC), 2.5 A (NO) |
| TW-H load ratings at 14 V DC | Resistive 15 A (NC/NO) · Lamp 3 A (NC), 1.5 A (NO) · Inductive 10 A (NC/NO) · Motor 5 A (NC), 2.5 A (NO) |
| TW-H load ratings at 30 V DC | Resistive 6 A (NC/NO) · Lamp 3 A (NC), 1.5 A (NO) · Inductive 5 A (NC/NO) · Motor 5 A (NC), 2.5 A (NO) |
| TW-H load ratings at 125 V DC | Resistive 0.5 A (NC/NO) · Lamp 0.5 A (NC), 0.5 A (NO) · Inductive 0.05 A (NC/NO) · Motor 0.05 A (NC), 0.05 A (NO) |
| TW-H load ratings at 250 V DC | Resistive 0.25 A (NC/NO) · Lamp 0.25 A (NC), 0.25 A (NO) · Inductive 0.03 A (NC/NO) · Motor 0.03 A (NC), 0.03 A (NO) |
| TW-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. |
| TW-L rated current (resistive) | 0.1 A at 125 VAC; 0.1 A at 8, 14 and 30 VDC |
| TW-L inrush current | 0.1 A maximum (NC and NO) |
| TW-L minimum applicable load | 1 mA at 5 VDC |
| TW-L operating range (micro load) | 5 to 30 V, 5 to 800 mW (26 mA maximum at 30 V) |
| TW-L contact resistance | 50 mΩ maximum (initial) |
| TW-L typical applications | PLC, telemetry and low voltage control |
Dimensions
Warning: Electrical Safety
The TW Series is a mains voltage device – incorrect installation can cause death or serious injury. All electrical work must be carried out by a licensed electrician.
Wire Length & Flow Sensitivity
The flow rate required to actuate the switch depends on many variables such as turbulence, liquid viscosity and the exact surface area of sensor wire exposed to the flow. The wire is made in fixed lengths of 50, 80, 100, 140, 160, 180, 200, 250 or 300 mm (2″ to 12″), measured from the tip of the wire to the bottom end face of the process connection, and the required length must be specified when ordering (e.g. TW-H-25B-SS-100). Use the online Paddle Trimming Calculator to find the optimum wire length: enter your pipe inside diameter, flow rate and liquid to check the switch will operate reliably at your flow.
Installation & Mounting
Mount in a pipe tee, tapping saddle or weld-on socket. For effluent or liquids carrying solids, use a stand-off tee (80 or 100 N/B) so the switch body sits out of the line of flow; the arrow on the switch must point in the direction of flow. The switch can go in suction or delivery pipework, horizontal or vertical. In vertical pipe, flow must be upward. Do not mount on the underside of horizontal pipe. Where possible, mount the switch away from pumps, valves and bends: a fitting directly upstream makes the flow uneven and turbulent at the wire sensor, which can shift the switching point slightly or make the wire flutter near the switching point, while downstream fittings have little effect. If the switch has to go close to a fitting, enter the upstream straight length in the Paddle Trimming Calculator and check operation on commissioning. 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.
Adjusting Sensitivity
Switches are supplied at maximum sensitivity (adjuster wound fully in). To decrease sensitivity, remove the red dust cap and wind the adjusting screw out (anti-clockwise) with a wide flat screwdriver. The further out the screw, the more flow is needed to operate the switch. Refit the dust cap.
Manual Override
A manual override is built into all TW Series models (TW-H and TW-L). Pressing the button lets the system be started manually at any time, and makes testing and commissioning very simple. To test after wiring, press the red manual override button under the cable gland — the switch changes state as if liquid were pushing the wire.
Hazardous Areas
The TW-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 TW-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.
When to use a Wire vs a Paddle
Choose a trailing-wire sensor when: (a) solids or semi-solids are present, or the fluid carries fibres or stringy debris that would foul a paddle (sewage pumping, slurry and mining applications); (b) the flow velocity is high and a conventional paddle-type switch is unsuitable (typical above 4 m/s in larger pipes); (c) you are sensing flow in open discharge applications or in pipes from 50 mm (2″) upwards, including pipes too large for a standard paddle (the TW handles 50 mm and up). For clean-water, low-velocity applications a paddle (F Series / FM Series) is usually more sensitive.
Approved Standards
The ‘H’ and ‘L’ microswitches used in the TW Series are approved to UL1054 (File E41515), CSA C22.2 No.55 (File LR21642) and EN61058-1, and are CE marked.
Serviceability
Easily serviceable and fully field-serviceable. The TW Series is very simple to service, and most components are available in spare part kits; spare parts are available from your supplier. The electrical housing detaches from the wet-end with a single screw without disturbing pipework. Replacement wires, seals and switches available from Kelco Engineering or your distributor.
