Flow switches are vital components in many systems, sometimes acting as critical safety features to prevent damage to pumps or other equipment. For this reason it is important to observe a few guidelines to ensure the control is installed correctly.

Why Is Proper Installation So Critical?

Like any control system, the proper operation of a flow switch is only as good as the data it receives. An improperly installed switch will read false information and will activate or deactivate at the wrong times.

A safety switch that doesn't trigger correctly could lead to equipment damage in cases such as a switch not shutting down a pump when a tank is empty. An improperly installed switch could also endanger worker safety. For example a sensor might be used to lock out a vessel when dangerous liquids are flowing to prevent workers from opening the vessel and being sprayed with toxic chemicals. If the switch doesn't trigger correctly, a worker might accidentally open the reactor vessel during operation.

A switch that triggers too often can also lead to problems such as wearing out a pump by cycling it too often or triggering alarms when no emergency condition exists.

Flow Switch Position

It is essential a switch be installed in a part of the pipe that has a steady flow profile. When liquids flow past a bend, tee or any fitting other than a horizontal section of straight pipe, the flow becomes turbulent. Turbulent flow leads to unreliable readings because of wildly varying flow velocities and can even damage the switch.

Instead, the switch should be installed at a point where the liquid has achieved laminar flow, a smooth and predictable flow profile. For a distance of approximately five pipe diameters downstream from any fitting that causes turbulence, the liquid is in a transition between turbulent and laminar flow so the readings are still unreliable. Flow switches should be placed beyond this transition point, meaning more than five pipe diameters downstream from any turbulence-causing fitting.

Pressure And Temperature

Flow switches are rated for ranges of temperature and pressure. This range not only ensures reliable readings but also protects the switch from damage. Exposing switches to temperatures and pressures outside these ranges leads to bad data and failed switches.

For example, fluid coming out of a reactor vessel may be hot. Although it may cool quickly, placing a flow detector right at the reactor vessel outlet might expose it to higher temperatures than it can handle. Pipes located outside may experience varying temperatures throughout the year as the ambient temperature changes so the entire range of possible temperatures should be considered.

Pressure can also change due to the presence of valves, pumps or other components of the system. The switch should be mounted in a position where pressure will remain stable and well within the operating range.