What are Flow Switches? Types of flow switches

What are the flow switches?

Flow switches are devices that monitor the flow through a channel and send a “trip signal” to various devices in the system, such as pumps.

The pump can be indicated by the flow switch to shut down or turn on. Some of the general uses are for the protection of the pump, protection of the cooling circuit and alarms for flow rates that are too high or too low.

Difference between Flow switches and Flowmeters:

The main difference between Flow switches and flowmeter is how they function.

The flowmeter continuously measure flow rates and user have to monitor these flow rates through monitoring devices attached to it or through the control system. Flowmeters themselves test the flow rate to detect if there are any issues, as and when rather than at a fixed set point.

While flow switch performs a designated operation example: pump) at a predetermined setpoint.

Types of flow switches:

Flow switches are also available of various types, such as flapper or paddle, target or disk or vane, diaphragm, shuttle, piston, etc.

1. Flapper or Paddle Type:

The flow switch consists of a paddle/flapper device hanging with the flat surface facing the direction of flow through a hinge. A permanent magnet is connected to this end; a reed contact above this magnet is located outside the fluid flow.

A second magnet with opposite poles produces the force needed to reset the switch to its original/normal starting point, i.e. a the no-flow location.

The force behind the flow causes the paddle/flapper assembly to swing away when the flow rises. This causes the magnet’s position to change in relation to the reed contact, triggering the contact.

2. Diaphragm Type Flow Switch

In construction, diaphragm type flow switches are similar to DP switches. The only difference is that there is a gap that allows fluid to flow through the transition between the inlet and the outlet port, while it is completely closed in DP switches.


Installing these switches allows the inlet port to be on the same line as the outlet port. The liquid flow usually takes a zigzag route inside the switch body when this is completed. This effect results in a significant drop in pressure, which happens when a liquid flows through the flow switch.

The spindle begins to rise or fall depending on the extent of the flow due to the movement of DP across the self-created orifice of the switch housing and the compression spring connected to the diaphragm assembly via a spindle.

3. Shuttle Type Flow Switch:

Shuttle style flow switches operate because of DP or the velocity of the liquid acting on a disk on the concept of a moving force.

A shuttle at the bottom and a magnet just above the disk are connected to the disk. The shuttle body’s upper part (spindle) is working against a spring of compression or gravitational force.

The shuttle is displaced as the liquid flow increases to the actuation area. This shuttle operates the reed switch inside the unit stem when displaced by fluid flow; the shuttle returns when the flow decreases and sits on the port seat.

4. Piston Type Flow Switch:

In this type of switch, a piston is positioned in the flow path.


The piston has a permanent magnet in it and travels with the piston. The magnet actuates the hermetically sealed reed switch mounted outside the mechanical structure but magnetically attached when and as long as the DP is strong enough to press the piston upside-down against the spring force.

The diameter of the piston-metering ground determines the clearance of the bypass and the point of action is set.