Flow switches are mechanical devices used to control the flow of air, steam, or liquids. Flow switches operate by relaying travel movements (relays, reed switches, paddles) to other machines within the system, usually pumps. The trip signal will show the pump to turn it on or off. It is necessary to provide damage protection and circuit cooling or adjust the flow rate that is too high or too low.
Flow Switches can serve a variety of functions and are also used in a variety of applications. If someone needs to monitor the flow rate or to protect the pump, then the flow switch can serve your purpose. The flow sensor will send electrical signals to the PLC or other electronic controller.
- Definition of Flow Switch
- Flow Switch function
- How Flow Switch works and what it types are
- Flow Switch Installation and Testing Flow Switch
- How Flow Switch Works By Type
- Flow Switch for Water and Liquids
- Flow Switch for Gas and Air
- Paddle-type Flow Switch
- Thermal Dispersion Flow Switches
- Oil Flow Switches
- Ultrasonic Flow Switch dan Non-intrusif
- Mechanical Flow Switches
- PVC Flow Switches
- Industrial Flow Switches
- Calorimetric Flow Switches
- Pneumatic Flow Switches
- Adjustable Flow Switches
- Rotary Flow Switches
Definition of Flow Switch
Flow switches are definiskan as flow or flow sensors that detect the absence of flow or flow in a closed or open flow system. Usually the flow switch will work to close or open if there is a flow or flow stop depending on the desired contact output nc or NO.
Because the flow switch function is considered as flow control, many also use the term flow control or flow control sensor. And in fact flow switch is a type of flow sensor, so many consider the flow switch the same as the flow sensor which is part of the flow meter sensor.
Thus, flow refers to the speed or physical movement of a gas, steam, or liquid inside a pipe that triggers the actuation of a flow switch. When there is no flow, the speed will drop or stop altogether; in both cases, the switch will return to its original position. Total stoppage or decrease in speed is indicated when there is no flow. Also, the stoppage allows the switch to return to its original position.
Flow Switch function
Flow switches are widely used to protect process systems that do not match the planned, in connection with the flow of a fluid, such as:
- Maintaining Production Quality from disrupted processes due to fluid flow quality
- Maintaining Damage Flow triggers such as pumps from over silence because the flow rate or flow velocity is not as required
- Keeping the engine from damage due to over heating due to the cooling flow system not as required
- and others
How Flow Switch works and what it types are
A flow switch is a device used to monitor the flow rate and pressure of a liquid, air, or other gas medium through a system. How flow switches work depends on the type of media and output measurements required. They usually consist of a primary mechanism, such as a paddle or magnetic trigger, that is connected to the sensor.
This mechanism is placed in the media stream. The flow causes the switch to be moved or the paddle rotated, sending a signal to a secondary component known as a transducer. The transducer takes the signal from the main mechanism, converts it into a more useful signal and passes it on to the transmitter. The reading is then compared to a preconfigured set of values and triggers any signal or action needed to adjust the behavior of components and mechanisms elsewhere.
Flow switches are used to monitor, report, and control the flow rate of media either through a specific part of a system or through the entire system, ensuring the flow remains within predefined parameters. If the rate exceeds or drops below what is required, it can be configured to trigger an external alarm, turn on the pump, activate the solenoid valve to divert the flow or even isolate parts of the system.
Flow Switch consists of a rowing system (1) that has a permanent magnet (2) located at its upper end. Reed contact (3) is positioned outside the stream above this magnet. Second, magnet (4) with opposite polarity is used to create a reset force.
The rowing system is moved after coming into contact with the flow to be monitored. Magnet (2) changes its position in relation to reed switch contact (3). Contacts open/close depending on the type of contact.
As soon as the flow is cut off, the paddle returns to its original position and the reed switch contact opens depending on the type of contact. This contact change (NO to NC or NC to NO) will be used to indicate the required flow signal output.
Flow switches are special electrical devices with a very simple design and small size. But despite its simplicity, flow switches play an important role in a variety of different applications.
These devices are used with the aim of protecting the pump and when the flow of air, gas or liquid through a particular line needs to be monitored, and alarms can be triggered with their help when needed. Switches may be specific to this type of application.
For flow switches that use sensors such as ultrasonic, electromagnetic or other sensors, the flow sensor will function as a switch. But for mechanical systems that usually use paddles that will move when there is flow or vice versa. This type of flow switch is like a general switch will provide contact when there is a flow or disconnect contact when there is no alira.
The disadvantage of this type of mechanical flow switch is usually somewhat less functional when the flow does not move but the pressure in the flow is still positive. This is different from flow switches that use electrified sensors such as ultrasonic types or magnetic sensors.
Another disadvantage of mechanical flow switches is that the large and small flow rate cannot be set with certainty, this is different from flow switches that use electrified sensors, the amount of flow felocity can usually be set by entering the maximum and minmal flow rate.
Also Read: Understanding and Function of Flow Meter
Flow Switch Applications on Machines and Processes
Flow switches are widely used to protect:
- Pumping machine from over heating motor and damage to pump pump seal due to empty pumped fluid
- Compressore both compressor chiler and air compressor to monitor the flow of lubricant oil compressor
- Condenser Cooling System in The Chiller System associated with cooling tower
- Over heating on bearing components due to cooling system is disrupted as in turbine plants, CNC Engine
- Over the hydraulic oil hetaing on the hydraulic press engine.
- Overheating in injection molding machines or similar
But in certain processes whose purpose is to help flow rate or total flow volume flow switch function has been found in flow tarsnmitter, especially when using digital flowmeters.
Why does flow switch show incorrect indications?
Below are the possible causes of incorrect flow switch activation:
- Trapped air or gas.
- Turbulence in a tube or unit
- The mechanical sensor assembly was damaged.
- The liquid is too thick.
- Do not use the equipment provided by the manufacturer.
Flow Switch Installation and Testing Flow Switch
Since there are so many different types of flow switches, as we will see in the next section, there are also various methods and techniques of installing flow switches. When looking for information on how to install flow switches, the most important thing is to have a clear understanding of what type of switch you are using and for what purpose.
However, there are some basic rules that apply to most methods of installing flow switches. Broadly speaking, these things include:
- Installing flow switches on a straight part of a pipe or channel
- Ensure there is a good straight pipe length in front of and behind the switch – ideally, equivalent to 10x the diameter of the pipe
- Avoid installing or installing flow switch cables near bends, other fittings, valves, sewers, narrower or wider sections of pipes, and other features that can cause clear fluctuations in flow rates through these areas.
Requiring the right methodology to install flow switches will depend on the type of switch you are using and where, the same goes for testing its function from any device already installed. To know how to test a flow switch, you need to know exactly what you’re testing.
In many cases, you’ll be able to make sure the Flow Switch is working properly simply by observing it in action and checking if the correct response is triggered when the flow starts or stops. In other cases, you may need to use an ohmmeter to measure the electronic resistance of the switch and confirm that there is a complete circuit (or ‘continuity’) registered when the switch is activated.
If any of the above steps don’t provide the necessary results, it may be time to replace or repair the switch. For certain types and locations of flow switches — including those attached to safety equipment such as fire sprinklers in public places — it is usually a legal obligation to test them regularly.
How Flow Switch Works By Type
There are many types of Flow Switches available, and each will take a subtle – but important – different approach to measuring the flow rate of a linear, nonlinear, volumetric or mass liquid or gas. Before ordering or installing a flow switch, it’s important to have a clear understanding of which specific type you need for the exact app you’re thinking about.
No one type or brand of flow switch will perform any flow switch task to the appropriate standard in any scenario, so you should know what type you need for the exact function it is meant to perform.
Flow Switch for Water and Liquids
Most water flow switches work by using a paddle — usually a physical one, but sometimes an ultrasonic flow meter — connected directly to a channel through which water or other liquids will pass through. The speed of the paddle’s movement will indicate the flow rate to the transducer, and the transmitter will, in turn, take this information and turn it into a signal or action.
There are different types of water flow switches available. In the section below, we’ll explore some of the more common ones:
Flow Switch for
Water Pumps
Flow Switches for water pumps are designed to make automatic and direct adjustments to the operating speed or volume transfer of the electric pump installed to the liquid system. By sensing the movement of gravity and the overall rate of water flow in the system, it can send a life/death signal to the pump which in turn raises or lowers the system’s internal water pressure.
It can also prevent the pump from becoming dry in the event of a water supply failure, which otherwise will quickly start damaging the pump.
Flow Switch for sprinklers
Sprinkler flow switches are most often – and most critically – found in automatic fire sprinkler systems. In this scenario, its main function is to detect when water passes through the sprinkler pipe and the valve exceeds the given flow rate, which indicates that the sprinkler system has been triggered.
This will then send a signal back to the fire department that they should go out and investigate. Most flow switches designed for this use also incorporate a snooze timer that will only send an emergency signal after a continuous flow is detected over a period of time. This is to avoid detection of false positives caused by unrelated or harmless pressure changes elsewhere on the system.
Magnetic Water Flow Switch
The Magnetic Water Flow Switch functions in accordance with Faraday’s Law of Electromagnetic Induction, which essentially states that the induced voltage is proportional to the speed of motion when a conductor (in this case water) passes through the magnetic field.
In short, the speed of movement and volume is measured by generating a magnetic field for water to pass through. This information is read by an electrical sensor, which in turn triggers an action based on reading.
For the magnetic water flow switch to function properly, the liquid passing through it must at least be somewhat conductive. They are often found in wastewater systems.
Inline Water Flow Switches
Inline Water Flow Switches are switches that are installed more permanently as an integral part of the entire system. This can be contrasted with an ‘insertion’ flow switch, which uses a probe or paddle inserted into the process pipe from the outside.
Inline Flow Switches tend to be more expensive and more complicated to install and maintain, but these switches require much shorter straight parts to function properly and can usually automatically condition the flow once installed.
Paddle Water Flow Switches
Paddle Water Flow Switches rely on physical probes or paddles to hang in pipes through which water or other liquids will pass through. These are then rotated or triggered at varying speeds and pressures depending on the rate of flow of material through the channel, and these signals are converted into readings and actions.
Paddle Flow Switch for water is excellent at measuring flow rates consistently and reliably, but is very sensitive to foreign bodies and residue buildup, and requires periodic maintenance due to wear and tear on its constantly moving parts.
Flow Switch for Gas and Air
Gas & Air Flow Switches can be used for air filtration and supply systems, duct heaters, exhaust vents, and more. Like its water equivalents, they can be designed as mechanical flow switches or non-intrusive varieties that sense the flow rate in other ways. In the following sections, we will discuss various examples of common uses of air and gas flow switches:
Air Flow Switch for ducts and HVAC
Airflow switches are found in all types of HVAC ducts and systems, often using paddle-type (mechanical) operations to trigger micro switches when flow increases or decreases beyond a set rate or volume.
In HVAC systems and ducts, many airflow switches can also be used to perform actions such as air handling, fan monitoring, and filter monitoring.
Paddle air Flow Switches
Just like paddle water flow switches, paddle air flow switches — sometimes known as propeller-type switches — are mechanical sensors that partially protrude into the monitored channel.
Gas and air delivered through the channel will physically move the paddle sitting directly in the airflow channel, and this, in turn, will trigger action when the flow increases or decreases beyond the desired speed.
Air Flow Switch for boilers
How the air flow switch works in the boiler will generally monitor the proper exhaust venting of the system by the fan through the chimney. These gases must be safely removed before the boiler is on, and boiler airflow switches are usually installed to only allow ignition after knowing that the fan is already rotating at the required speed.
If the clogged chimney or fan is not working properly, the airflow switch will detect that the pressure has not quite dropped, and will not let the boiler turn on until the problem is resolved.
Paddle-type Flow Switch
Flow Switch Paddle is a type of mechanical switch that is activated directly by pressure from a medium — usually a liquid — that passes through the channel or channel on which the switch is inserted. Paddles are often small pieces of metal or plastic that hang inside pipes and are attached to a tightened spring or a series of magnets.
In its resting position, it is considered open or closed, depending on the function of the switch and larger parts of the system. Any media that passes through the channel with enough force (or not enough) to move the flow switch paddle to the second position will complete the circuit, and trigger an action response or alarm.
Thermal Dispersion Flow Switches
A thermal dispersion flow switch is a ‘solid state’ device, meaning it contains no moving parts (as opposed to a mechanical paddle – or propeller type product). A thermal flow switch involves a sensor probe inserted into a flow center in a line or pipe.
The probe is heated continuously through an electrical wattage input, and the thermal dispersion principle allows the flow rate of a gas or liquid to be calculated according to how quickly the heat is ‘carried’ by the molecules flowing through it.
The number of watts that must be sent to the probe to maintain a consistent temperature provides the numbers necessary for the flow rate calculated very accurately. In addition to accuracy, thermal dispersion flow switches are valued for their flexibility (measuring very low and very high flow rates), their roughness, and ease of insertion.
Oil Flow Switches
Oil Flow Switches or oils work exactly like other liquid flow switches – and as such, these switches come in a variety of configurations, with the most common paddle or thermal variants.
Switches designed for use with fuel and oil tend to be somewhat more wear-resistant than versions aimed at less aggressive media, and can usually operate at higher temperatures with stronger seals and containers.
Ultrasonic Flow Switch dan Non-intrusif
Ultrasonic Flow Switch and Non-Intrusive are popular variations of non-intrusive flow switches, which means these switches don’t really have to penetrate the walls of the pipes, channels, or channels you’re trying to monitor the flow of.
Instead, the ultrasonic version can be clamped to the outside of the channel, where it reads and reacts to the flow rate by pinging signals back and forth from the sensor. This signal is refracted and reflected by particulates or bubbles in the stream, before returning to the sensor, and the flow rate can then be calculated using the Doppler effect. (The Doppler effect is the reason why ambulance sirens seem to change the tone as they pass you on the road!)
Because ultrasonic flow switches generally rely on particulates or aeration in liquids, they tend not to be suitable for drinking water or distilled water, and are more commonly found to monitor wastewater and other ‘dirty’ media. Tong varieties will only work with certain types of ducts due to the risk of signal interference, and are rarely seen on lined pipes for that reason.
Mechanical Flow Switches
Mechanical Flow Switches are all types of switches that have one or more moving parts triggered by direct physical contact with the monitored medium. They usually work with the movement of the components that cause the circuit to complete, which in turn triggers the necessary action or response.
Paddle type flow switches are a common example of mechanical flow switches. Mechanical switches need to be tested and replaced periodically, as the continuous physical movement of the parts ultimately leads to wear and tear that can affect operation.
PVC Flow Switches
Flow Switch PVC is the most basic type of product for this application and is usually preferred where quick visual confirmation of flow status/no flow is required. PVC flow switches are usually mechanical and can be propeller or magnet types with one or more moving parts.
They tend to be economical enough to be installed, and generally quite sturdy in construction. They are usually designed to facilitate cleaning and maintenance as well as offer good chemical compatibility and anti-corrosive properties.
Industrial Flow Switches
Industrial flow switches tend to be larger, more powerful versions of many of the types of flow switches outlined above. They are usually able to withstand much higher volume, pressure, and flow rates, and are often designed to handle materials that are much more aggressive, highly contaminated, or harmful.
Industrial flow switches often avoid magnetic operating parts, in order to function properly with water containing rust and other metal particulates.
Calorimetric Flow Switches
Understanding how caloriemetric flow switches work is quite simple if you already understand the closely related thermal dispersion equivalent function. The calorimetry switch uses two temperature sensors, one of which is heated and one of which monitors the temperature of the media environment in the channel.
When the difference between these two readings is compared, the flow rate can be calculated again – faster flow will result in a smaller difference, since heat is carried faster than the sensor is warmed below the higher flow rate.
Pneumatic Flow Switches
Pneumatic Flow Switches generally replace air valves for mechanical switches or paddle types and can be used to control airflow through relays or valves when flow starts or stops.
Air valves will often be set to remove pressure from the system if the flow rate drops to a level that is too low. Pneumatic flow switches are also useful in applications where there is a required pressure difference between different areas of the channel.
Adjustable Flow Switches
Customizable Flow Switches are all types of devices that allow users to quickly and easily recalibrate desired flow settings without unpacking the unit. This is usually done with a flat screwdriver, opening or closing to adjust the sensitivity of the propeller or paddle located inside the switch house.
Rotary Flow Switches
Rotary Flow Switches serve as basic turbines, generally in the form of many bladed wheels or paddle wheels mounted entirely inside a stream of channels on free-spinning pads. It records the rate of flow when a liquid (the most common medium for a rotary flow switch) passes through it. They are available in impeller, piston (shunt) and paddlewheel designs.
Thus the article from “How Flow Switch Works” Hopefully can answer all reader questions and further add new insights from the “Flow Switch Way” that has not been recognized, May it be useful.