TW SeriesTrailing-Wire Flow Switch
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.
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 retired and replaced by the TW-L. A manual override is built into all TW Series models.
More Information
- TW Series Data Sheet
- TW-H Series Installation Sheet
- TW-L Series Installation Sheet (low voltage)
- Fitting it in a standoff? Standoff check
3D CAD models (6 models, STEP)
Simplified external models for layout and fitting; not for manufacture. -XXX: one model covers every wire length.
- TW-H-25B-SS-XXX7.4 MB
- TW-H-25B-XXX8.8 MB
- TW-H-25N-XXX8.5 MB
- TW-L-25B-SS-XXX7.4 MB
- TW-L-25B-XXX8.8 MB
- TW-L-25N-XXX8.5 MB
How the TW Series trailing wire responds to flow
No flow: the 2 mm stainless steel wire hangs at rest.
Ordering — Available Models
Operating Limitations
Electrical Data
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.
