A basic flow switch detects gas flow in pipes through the use of a mechanical or electronic mechanism. The main goal is to sense the movement or pressure change caused by the flowing gas and then trigger a response, typically in the form of an electrical signal. Here's a general overview of how a basic flow switch works:
Mechanical Flow Switch:
In a mechanical flow switch, the movement of the gas itself activates the switch. One common design involves a vane or paddle located within the pipe. When gas flows through the pipe, it causes the vane to move. The movement of the vane then triggers the switch to open or close. This can complete or interrupt an electrical circuit, sending a signal to a control system or an indicator.
Additionally, there are designs that use a flexible diaphragm or bellows mechanism. The pressure difference between the incoming and outgoing gas causes the diaphragm to flex, activating the switch.
Electronic Flow Switch:
Electronic flow switches utilize various sensors to detect the gas flow and then generate an electrical signal. Some common types of sensors used for this purpose include:
Thermal Sensors: These sensors measure the change in temperature caused by the flowing gas. As gas flows, it carries away heat from a heated element, leading to a temperature difference that can be detected electronically.
Ultrasonic Sensors: Ultrasonic sensors emit sound waves into the gas stream and measure the time it takes for the waves to bounce back after hitting gas molecules. Changes in the time taken indicate variations in flow velocity.
Differential Pressure Sensors: These sensors measure the pressure difference between two points in the pipe. As gas flows, it creates a pressure drop, which can be correlated with the flow rate.
Vortex Shedding Sensors: These sensors utilize the vortex shedding phenomenon, where the gas flow creates alternating vortices behind an obstruction. The frequency of vortex shedding is proportional to the flow rate and can be detected electronically.
Signal Transmission:
Once the mechanical or electronic mechanism detects the gas flow, it sends a signal to a control system, which can then trigger various actions. These actions could include activating alarms, shutting down the gas supply, adjusting valves, or starting/stopping equipment dependent on the gas flow.
It's important to note that the choice of flow switch depends on factors such as the type of gas, pipe diameter, flow rate, pressure, and the sensitivity of detection required. Additionally, safety considerations are critical when dealing with gas flow detection to prevent leaks, accidents, or disruptions in the gas supply system.