How Does a Flow Switch Work?
Flow switches are mechanical devices; used in monitoring the flow of air, steam or liquid. A flow switch operates by conveying a trip motion (relay, reed switch, paddle) to another machine within the system, i.e. a pump. The trip signal will indicate to the pump to turn on or turn off. It is necessary to provide cooling-circuit and damage protection or for alarms with flow rates that are too high or too low.
What is “flow”?
Flow refers to the velocity or physical movement of gas, steam or liquid within a pipe that triggers the actuation of the flow switch. When there is no flow present, velocity drops or there is complete stoppage; in either case, the switch will revert to its original position.
What are some uses of flow switches?
A liquid flow switch is applicable in chlorination of a swimming pool, hot water heating, air conditioning, liquid transfer systems, fire sprinkler systems and industrial laser cooling systems.
Water flow switches are implemented in the water sprinkler systems. For example, in the case of a fire, a flow switch can signal to an electrical fire alarm device to trigger on in the building.
Air flow switches are used to clean room filter systems, exhaust ventilation, and air treatment systems.
Other examples of where flow switches are used:
> Water treatment systems
> Additive or blending systems
> Fire sprinkler systems
> Air supply systems
> Duct type heating
What are some of the functions of a flow switch?
Flow switches perform precise functions based on requirements. For instance, it is capable of stopping a motor completely when there is no flow. It can also trigger a motor to start up when the flow starts. It can also sound an alarm when the flow arrests or turn off the alarm when the flow rate is appropriate.
What are some considerations?
Since flow switches play such an integral role in the industry, measuring flow rate accurately is very important. The flow rate of liquids can be inferred by calculating the change in dynamic energy or velocity. The velocity is dependent upon the pressure differential that forces the liquid through the conduit or pipe. Since the cross-sectional area of a pipe is constant and known, the velocity will be a good indication of the flow rate. Calculating the flow rate is imperative as it helps to set flow switches to a pre-determined close function.
What are some types of flow switches?
Vane-operated flow switch- relies on a fluid pushing against the paddle in the liquid flow. As the flow drops to pre-set levels, it triggers an internal magnetic mechanical and coupling switch actuation lever which essentially trips the switch.
Variable are flow switch- has an internal piston which activates the switch. The flow will enter a port which adds pressure to the magnetic poppet. As the flow pressure hits a preset level, the switch will turn off.
Ultrasonic (Doppler) flow switch– is affixed to the outside of a pipe. Ultrasonic sensors send signals when it detects a change in the flow.