Flow switch STFS 15 STFS 20 STFS25

The STFS series is the sealed, higher-protection version of the paddle flow switch, rated IP65 and suitable for outdoor installation, plant rooms with washdown, and any location where the standard IP54 housing would take in water.

Three sizes cover 1/2, 3/4 and 1 inch pipe, each supplied with a set of four paddles so the switch can be trimmed to the pipe diameter. The wider rating is the important difference from the standard range: fluid temperature runs from -25 C to +120 C, which covers chilled water and glycol circuits at one end and hot water at the other without changing the switch, and maximum working pressure is 1.5 MPa.

These are used on chilled water circuits where the switch is interlocked with the compressor, on heat pump water circuits, and on any installation where the switch is exposed rather than tucked inside a plant room. The trip point is adjustable, so the switch can be set to prove flow at the actual duty rather than at a nominal rate.

Practical points on installation: fit in a straight section with the arrow following flow and at least five pipe diameters downstream of an elbow, so the paddle is not sitting in turbulence; keep the paddle clear of the far wall of the pipe - a paddle that touches the wall reads flow when the pump is off and defeats the interlock.

The IP65 rating protects the enclosure, not the paddle. These switches must not be installed where the liquid can freeze: ice in the pipe will bend or break the paddle, and the failure is usually discovered only when the evaporator has already frozen.