TWM Series

The TWM 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.

All TWM-H and TWM-L models include a built-in manual override button. 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. To test after wiring, press the red manual override button under the cable gland; the switch changes state as if liquid were pushing the trailing wire.

The flow rate required to actuate the TWM depends on many variables such as turbulence, liquid viscosity and the 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, 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. TWM-H-25B-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.

Open the Paddle Calculator →

Mount in a pipe tee, tapping saddle or weld-on socket. For effluent or liquids carrying solids, use a stand-off tee (50 mm (2″) or larger) 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 suits full or partially full pipe and 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.

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.

The TWM has an aluminium housing. For all mains voltage applications it must be earthed using the dedicated earth terminal inside the housing.

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 for many normal pumping situations where the flow velocity is high and paddles are unsuitable. Designed for the toughest paddle-unsuitable services: sewage pumps where rags and fibres would foul a paddle, slurries with abrasive solids, and mining applications with high-velocity dirty water. The flexible wire flexes with the flow, accumulates less debris, and survives velocities that fatigue a paddle.

The TWM-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 TWM-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.

The trailing wire sensor and its arm and pivot bearing are replaceable items. Spare parts, including replacement trailing wire sensors and arm assemblies, are available from your supplier; quote the part number of the trailing wire switch when ordering. To replace the wire, unscrew it from the main switch arm using the spanner flats on its top screw (right-hand thread), fit the replacement and fully tighten the screw (a drop of Loctite Stud Lock can be added for extra security; the small O-ring on the screw normally acts as a lock washer). Replacement arms are supplied complete with a new bronze bearing and are held by a pivot bolt in the side of the process adaptor. Never undo or remove the sealed hexagonal cap at the top of the main arm — it contains a magnet oriented for proper operation of the switch.

The ‘H’ and ‘L’ microswitches used in the TWM Series are approved to UL1054 (File E41515), CSA C22.2 No.55 (File LR21642) and EN61058-1, and are CE marked.