What is a flow switch on a pressure washer & how does it work?

The flow switch is a safety device, which prevents the burner from firing when water flow is interrupted. The switch goes into the fluid system so that water flows through it when the system is operating and the trigger gun valve is open. Water flow moves a magnet into the flow switch and the magnet holds a reed switch closed when there is water flow. When water flow stops the magnet moves from the reed switch, which will open and break the electrical circuit to the burner system.

A flow switch has three components: a metal body, the magnet and a reed switch. The switch closes when the magnet is close to the switch. It pulls its two thin, wire connectors together to complete an electrical circuit. The flow switch is centered around the action of the magnet which travels from one end of the fluid handling portion of the metal housing to another. The magnet has a hole in the center that lets water flow through it. The size of the magnet and the space between the sides and the body will determine the volume of water flow needed to lift the magnet. A larger hole means a larger volume is needed to move the magnet and a smaller hole means a smaller volume is needed. 

Since the tube that the magnet travels through is not all the way blocked off, water volume flowing through it rather than pressure against the magnet, prompts the magnet’s movement in its housing. The magnet will not move until the volume of moving water is sufficient to lift its mass. The distance of magnet movement is proportionate to the rate of water flow

The reed switch consists of two thin and wire-like contractors, which are put parallel to the magnet’s path. When the magnet comes to the opposite or the correct distance from the contractors, the magnetic field pulls the two contacts together. The extremely small reed switch contacts are set just far enough apart to keep current from jumping between the contractors. The reed switch must be used in a low amperage situation and should be in a control circuit separate from the motor circuit. 

Our flow switch recommendations: 

Our sister company, Aqua Jet Mobile Pressure Washing has tried several types of flow switches with our pressure washer. Through trial and error we were able to find flow switches that we found to be the perfect fit for us, so we wanted to share what and where to get these from. 

Vertical flow switches 

Envirospec LLC: https://envirospec.com/burners-burner-repair-parts/#flowswitch

BCE Cleaning Systems: https://www.bcesystems.com/store/p464/ST-5V_-%22Suttner%22_Flow_Switch.html#/

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If you currently live in Utah and are needing pressure washing services, contact our sister company, AJET Services (801-330-0398 or contact@ajetservices.com).