Flow switch

The flow switch is designed to monitor the flow of air, liquid or steam. The device transmits a trip signal through to another device in the system, called a pump. Flow switches are typically built to indicate to the pump regarding shutting off or to turn on. A flow switch has several different uses. 

Flow Switch is a mechanical switch that is switched on or off in response to the flow or non-flow of a fluid such as air or water. The switch typically operates through the use of a paddle which gets displaced due to the force of fluid moving past it.

flow switches are used to determine if the flow rate is above or below a certain flow rate. This value (the set point) can be fixed or adjustable. When the set point is reached, the response can be the actuation of an electric circuit.

Why Flow switch Shows wrong indication ?

The below are the possible causes for the false activation of flow switch :

• Entrapped air or gas.
• Turbulence in tubing or unit
• Mechanical sensor assembly damaged.
• Liquid is too viscous.
• Not using the fittings supplied by the manufacturer.

different types of flow switch

Paddle flow switch

Paddle flow switches or vane sensors with an electrical contact output are at a specific flow rate. Dwyer flow switches are economical and reliable. Applications include proof of boiler flow, air conditioning, controlling of dampers according to flow, and protecting pumps, motors and other equipment against low or no flow.

Shuttle / Piston flow switch

Shuttle or piston flow switches are sensors with an electrical contact output at a specific flow rate. Models are used with oil, air, water and gases. Applications include oil flow control, low flow detection in cooling lines, and high pressure lubrication systems. Rugged construction and excellent chemical compatibility simplify flow/no flow detection.

Thermal flow switch

Thermal flow switches are sensors with an electrical contact output at a specific flow rate. Dwyer models provide a complete system for leak detection and feature a selectable NO or NC operation. Applications include chillers, hot water heaters, and liquid transfer systems.

Piezo flow switch

Piezo flow switches are sensors with an electrical contact output. The bulk flow monitor provides effective monitoring for most flow/no flow conditions in pipes. Applications include oil spray systems, rotary drums, distributors, and food processing. Dwyer's piezo flow switch offers many features that exceed the industry standards.

What is a flow switch?

A flow switch is a mechanical instrument that is used to control the flow of air, steam or liquid. Flow switches work by sending trip signals to another device (a pump for example) within the system, telling it to shut off or to turn on, which will further protect it from damage and for cooling circuit protection.

Flow switches determine if flow is above or below a certain rate, known as a set point. The set point can either be adjustable or fixed, depending on the specification of the individual instrument. When the set point is reached, the response is often the actuation of an electric circuit. Once tripped, the flow switch stays in its new state until the fall falls below the set point.

Construction

Working

One type of flow switch, uses a pivoted arm that has contacts on one end and a paddle 

or flag on the other end. The end with the paddle or flag is inserted into the pipe so 

that the flow of liquid or gas causes a lever to move and open or close the contacts.

Symbol

Applications

These switches find application in the detection of fluid flow and measurement of fan speeds.

A flow switch might be used to protect a central heating system electric heating element from being energized before the air flow from the blower is established.

Flow switches might also be used to alarm if a ventilation fan in a hazardous location fails and air flow has stopped.

• Pump protection
• Safety spray nozzle monitoring
• Cooling water or heat exchangers
• Oil well system testing
• Drain line flow
• Relief valve monitoring
• Water Treatment Chemicals
• Cooling System
• Heat Pumps
• Fire Control System