What is a flow switch?
The flow switch is mainly installed online or plug-in into water, gas, oil, and other medium pipelines to monitor the water flow in the water system. When the water flow rate is higher or lower than a certain set point, the alarm signal is triggered and sent to the unit, and the system can make corresponding instructions after obtaining the signal. Avoid or reduce host "dry burning".
First, there is a fluid channel in the flow switch, which is inside the housing, and on the channel is a piston with a permanent magnet inside. When working, the fluid will give a certain pressure. When the piston is pushed by the pressure difference caused by the liquid flow, the magnetic piston will make the sealed reed switch inside the equipment move. The diameter of the piston determines the starting flow. If the flow decreases, the pressure changes, and the stainless steel spring push the piston back. If the reed switch is actuated, it can be used for remote alarm or indication, and it can also be integrated into the automatic control system.
How a Flow Switch Works?
The flow switch is to command the switch of the system according to the flow.
Set the upper limit or lower limit for the flow switch. When the flow reaches the limit value, the flow switch will send out a signal or alarm, and the system will run or stop. Generally, systems that require flow will use a flow switch.
Depending on the system, the flow switch model, and other factors, the place of use is also different, and it depends on the specific situation.
Working principle of water flow switch When there is water flowing in the water flow switch and the water flow rate is ≥1.0L/min, the magnetic core in the water flow switch is pushed by the water flow to generate displacement, and the displacement of the magnetic core drives the magnetic source to produce a magnetic control effect to make the output of the water flow switch "on". "Signal. The flow switch is included in the quick and easy automatic selection. The signal is input into the equipment control system, and the control function is realized through the control system.
When the water flow is less than the starting flow, the water flow switch outputs an "off" signal. The control system produces the opposite controller action to the above. In other words: water flow switch When the water flow in the pipeline is greater than 1L/min flow, the magnetic core will be displaced under the action of water flow and drive the magnetic source to produce a magnetic control effect, so that the sensor outputs a "1" switch signal, which is input into the equipment control system achieves the purpose of water flow control after power amplification.
When the water flow in the pipeline is less than 1L/min, the magnetic core drives the magnetic source back under the thrust of the return spring, so that the sensor outputs a "0" switch signal and stops the system. The flow switch has the advantages of high sensitivity and strong durability.
The difference between flow meter and flow switch
A flow meter is a device used to measure the flow rate or gas/liquid movement in a pipeline called a flow meter. In other words, it is an instrument used to monitor, measure, and record the flow, pressure, or discharge rate of a liquid/gas.
Examples of flow meters:
★ Differential pressure flow meter (splitter plate, Venturi flow meter, flow nozzle, Rotameter)
★ Positive displacement flow meter (piston flow meter, gear flow meter, screw flow meter)★ Open channel flow meter (flue, weir, sluice)
★ Electromagnetic flow meter (pipeline), etc.
However, a flow switch is a mechanical device used to control the flow of air/steam/liquid is called a flow switch. The flow switch transmits a trip signal to other equipment in the system (usually a pump) to shut down or open. This helps protect against damage to the system and protects the cooling circuits in the system. Flow switches are used to trigger alarms and control relays.
Flow switch examples:★ Water flow switch: for sprinkler system
★ Air flow Switches: Used in room filtration systems, air handling, exhaust ventilation systems, etc.
Types of Flow Switch
1.Baffled Flow Switch
A baffled flow switch or plug-in flow switch is also called a mechanical flow switch.
(1) The mechanical part of the baffle-type flow switch is safely isolated from the electronic part.
(2)The baffle-type flow switch does not contain bellows that may easily cause failure.
(3)The electrical parts of the baffle-type flow switch do not have direct contact with the metal parts with large temperature differences, so there will be no problem of corrosion caused by condensed water generated by the electrical parts.
(4)The baffle-type flow switch uses an imported magnetic sensitive switch as the electrical activity part, which has a small disconnection and reset flow.
1.2 Installation guide
The installation position of the baffle-type flow switch is generally installed in the pipeline from the water outlet of the water pump to the water outlet of the equipment, and cannot be installed on the pipeline of the suction inlet of the water pump. This will make the water pump unable to absorb water normally and the water flow switch cannot be opened. Special attention should be paid to this point. The baffle-type flow switch allows horizontal (the wire part up) and vertical installation.
Gas-liquid dual-purpose type can be widely used in industrial automation/mechanical equipment/air compression industry/refrigeration and air-conditioning fields. In industrial occasions, it is specifically used in water-cooled welding machines, laser equipment cooling systems, vacuum coating machines, electric furnaces, polysilicon ingot furnaces, etc. . The flow switch magnet is not in a flowing waterway, it can be used in a sewage system and will work properly.
1.4 Technical Parameters
△ Voltage: 250V (max.)△ Maximum current and capacity: 1A, 50 VA
△ Wiring method: direct attachment
△ Output: SPST magnetic switch (factory setting normally open)
△ Pressure resistance: 25 bar, 50 bar can be customized
△ Average pressure loss: 0.01 bar (at maximum flow rate)
△ Working temperature: -20...90°C (150°C can be customized)
△ Enclosure protection grade: IP65
△ Material: Wetted body: Nickel-plated brass
△ Bezel: Beryllium Copper
2.Thermal Flow Switch
The thermal flow switch is also called an electronic flow switch.
★ Relay/transistor/4-20mA output
★ No fluid obstruction, no pressure drop, no maintenance
★ 6 LEDs display alarm and flow status
★ Temperature compensation in the whole temperature zone;
★ Switch output, control point continuously adjustable on site;
★ Easy to install, the product is suitable for various pipe diameter requirements;
The flow switch can monitor the liquid flow in the pipeline in real time, provide switch output, use 6 LEDs to display the fluid flow rate in real time, and realize the following monitoring functions:
★ Medium flow, reduce/increase flow rate;
★ medium presence/absence;★ medium flow/stationary;
It can be used to monitor the flow rate of the fluid in the pipeline, monitor the flow interruption, or prevent the pump from running dry. It is widely used in various industries where it is necessary to monitor the fluid flow rate in the pipeline or to protect important equipment when the liquid flow fails.
2.2 Working Principle of The Thermal Flow Switch
The thermal flow switch is designed based on the principle of temperature change of the probe head. Built-in heat sensor and thermal sensor in the probe, and contact with the medium. When measuring, the heating sensor emits constant heat. When there is no medium flowing in the pipeline, the heat received by the thermal sensor is a constant value. When there is a medium flowing, the heat received by the thermal sensor will change with the flow rate of the medium. Change, the thermal sensor converts the temperature difference signal into an electrical signal and then converts it into a corresponding contact signal or analog signal through a circuit.
Thermal diffusion flow switch principle, thermal diffusion technology is a technology with excellent performance and high reliability under harsh conditions. Its typical principle is that when two sensing elements are placed in the fluid, one of them is heated and the other is used in the sensing process temperature. The temperature difference between the two sensing elements is related to the process flow rate and the nature of the process medium. The temperature difference between the two sensing elements is greatest at no flow, but as the flow increases, the heated sensing element cools down and the temperature difference decreases. The fluid flow rate directly affects the degree of heat dissipation.
2.3 Technical Parameters
△ Setting range: 1~150cm/s (water), 3~300cm/s (oil), 20~3m/s (air)
△ Signal output: PNP, NPN, relay, analog (4~20mA)
△ Power supply: 24V±20%DC
△ Switching current: 400 mA max (PNP or NPN type), 1A@24V ac/dc max (relay type)
△ No-load current: maximum 80 mA
△ Flow indication: LED row (6)
△ Setting method: potentiometer setting
△ Pressure range: 100 bar
△ Medium temperature change: ≤4℃/s
△ Response time: 1~13s, typical value 2s
△ Initialization time: about 8s
△ Electrical protection: reverse phase, short circuit, overload protection
△ Protection class: IP67
△ Medium temperature: -20~80℃
△ Ambient temperature: -20~80℃
△ Storage temperature: -20~100℃
△ Material: probe: stainless steel 304 (optional 316L), shell: stainless steel 304
△ Built-in 4311 technical parameters: Measuring range: 0-20 cm/sec to 1-100 cm/sec can be continuously adjusted. (relevant to water, for other media, the range is extended)
△ Measurement time: 2-10 seconds, according to measurement conditions
△ Linearity deviation: <5% (best-fit slope)
△ Repeatability Tolerance: <2%
△ Temperature drift: <3%/K
△ Power supply voltage: 24V DC ± 10%
△ Current consumption: 100 mA max
△ Output current: 4-20mA
△ Resistive load: 0-600 ohms
2.4 Related Information
Switching value (D): It is a digital signal. Generally speaking, there are two states of switching: high level and low level (that is, on and off, 1 and 0, etc.);
Analog (A): It is an analog signal, that is, a general voltage or current signal.
Voltage signal: Measure the flow rate and convert it into a 1~5V voltage signal, which is an analog quantity.
Current signal: Measure the flow rate and convert it into a 4~20mA current signal, which is also an analog quantity.
3.Differential Pressure Switch
For the measurement of water flow, the accurate flow rate can be obtained by measuring the pressure drop at both ends of the valve, orifice plate, etc., and then check the pressure drop and flow curve of the valve or orifice plate. The flow rate is obtained by the method of pressure drop. From 2003 the first use to 2013, it has been widely used in HVAC water side systems and flow measurement instruments. The application of differential pressure switches in the HVAC system is mainly controlled according to the resistance and flow curve of HVAC equipment. , Water filters, valves, and water pumps all have their performance curves of pressure drop and flow.
As long as the measured pressure difference on both sides of the differential pressure switch is compared with the preset value, the flow can be accurately controlled. The differential pressure switch used as flow control in HVAC has the characteristics of accurate flow control, no additional resistance to the water system, no requirements on the diameter of the water pipe, and no disturbance of water flow. It can replace any form of a target flow switch. Because of the target flow switch, it can avoid false flow caused by pump cavitation, and has a very accurate reset flow and cut-off flow.
It can be widely used in large, medium, and small air-cooled or water-cooled chillers using plate heat exchangers, casing heat exchangers, and shell-and-tube heat exchangers for water flow control and status monitoring of water pumps and water filters.
3.3 Technical Parameters
△ Using medium temperature range: -20~93℃
△ High and low voltage side connection ports: 1/4 SAE (7/16-20UNF), G1/4, etc. optional
△ Maximum allowable static pressure: 10 bar (20 bar can be customized)
△ Maximum allowable pressure difference: 5bar (8bar can be customized)
△ Set point repeatability deviation: ±1%
△ Output form: a set of SPDT dry contact output, (factory standard two-wire normally open output, three-wire normally open and normally closed output optional)
△ Switch parameter: 10A (max.) 250V (max.)
△ Wiring method: 105℃ flame retardant sheathed wire 2X0.75mm2 or 3X0.75mm2 optional
△ Enclosure protection grade: IP54
An infrared water flow switch, also called an infrared water flow sensor, is used in the new high-tech industry in the water heater industry, that is, the water inlet of thermoelectric water heaters, to detect the flow of water entering the instant electric water heater, and to control the startup and shutdown functions. It is especially suitable as a supporting device for constant temperature, instant electric water heaters, which can transmit the detected water flow and temperature to the control system in time to achieve the purpose of rapid constant temperature. It is also suitable for the flow detection requirements of similar products.
3.4 Installation Guide
(1) The factory adjustment of the water flow switch is near the minimum flow value, and it must not be adjusted lower than the factory setting position during use, otherwise the switch will not return to the "no liquid flow" position.
(2)To increase the flow rate, turn the adjusting screw clockwise. If you want to lower the flow rate after increasing the factory setting value, you can turn the adjusting screw counterclockwise.
(3)After the adjustment is completed, check that the set value of the flow switch is not lower than the factory set value. By pressing the main lever several times, check whether there is a "click" sound when the main lever returns. The clock rotates the adjustment screw until the lever returns with a "click".
(4)The set screw for sealing paint cannot be adjusted. Once changed, it will destroy the control of the flow switch or cause the adjustment to fail and fail to work.(5)The flow adjustment is too high. When the flow is low, the flow direction piece cannot be driven, and the switch cannot operate. The flow adjustment is too low, and the switch is too sensitive, resulting in malfunction.
How to Choose the Right Flow Switch for Your Needs?
To choose a suitable flow switch or liquid level gauge, in addition to selecting the function according to your own needs, you should also select a reasonable type according to the characteristics of the fluid working condition, installation requirements, environmental conditions, economy, and other factors.
(1) Installation environment. The on-site installation environment mainly refers to the measurement of the diameter of the pipe, the length of the straight pipe section, whether there is vibration in the pipe, whether there is strong magnetic field interference and high-temperature radiation heat around, etc.
(2) Safety, to prevent accidents. For example, when measuring corrosive media, the appropriate lining material should be selected according to the corrosive strength, and the explosion-proof instrument should be used in the environment of flammable gas.
(3) Energy saving. The pressure loss before and after the fluid passes through the flow meter, the smaller the pressure loss value, the better the energy saving. Non-contact flow meters such as ultrasonic flow meters, electromagnetic flow meters, and elbow flow meters have no pressure loss.
(4)Fluid properties. Fluid properties mainly refer to a fluid composition, temperature, pressure, viscosity, etc. Confirm the selection range step by step according to the actual situation. First of all, it is distinguished from the composition (liquid, gas, steam, degree of dirty flow), differential pressure flow meter and vortex flow meter are basically adapt to the above fluids.
(5) Accuracy and economy. Generally, flow meters with relatively stable performance, good repeatability, long service life and wide turn down ratio range are beneficial to increase the adjustment of process equipment measurement parameters in the later stage, thereby reducing investment.
The Benefits of Using a Flow Switch in Your Facility
(1)Improved efficiency: Flow switches can be used to optimize process control, ensuring that the right amount of fluid is flowing through the system at all times. This can help reduce energy consumption and improve the overall efficiency of the facility.
(2)Enhanced safety: Flow switches can be used to detect abnormal flow rates or blockages in the system, which can help prevent accidents or equipment damage.
(3)Better process control: Flow switches can be used to trigger alarms or shut off systems in the event of a problem, helping to maintain control over the process and minimize disruptions.
(4)Cost savings: By improving efficiency and reducing the risk of accidents or equipment damage, flow switches can help a facility save money on energy costs and repairs.
(5)Increased reliability: By continuously monitoring the flow rate or velocity of a fluid, flow switches can help ensure that the system is operating at peak performance, which can improve reliability and uptime.
Maintaining and Troubleshooting Your Flow Switch
(1) In general, mechanical flow switches cannot be used for flow switches in muddy water, and electronic flow switches (thermal conductivity or ultrasonic) with stainless steel shells should be used more suitable. Because since it is a muddy water pipeline, the fluid in the pipeline has impurities, and the principle of using a mechanical flow switch is that the baffle is washed away by the fluid and restored, and the muddy water will make the baffle insensitive, resulting in unsatisfactory use results.
This situation does not exist in the electronic flow switch, but the price of ultrasonic in the electronic type is relatively expensive. In terms of comprehensive cost performance, the electronic heat conduction type will account for the majority.
(2) The flow switch is a kind of flow sensor. The flow sensor can measure the specific flow value. The flow switch does not need to measure its specific flow value, but the flow sensor sets a value, and when the value exceeds this value, it outputs a switch value to achieve the function of opening and closing.
(3) Some flow switches have a fixed value and cannot be changed. The upper and lower limits of the flow switch are set by the manufacturer according to the needs.(4) The flow switch generally has no power supply, a simple contact is enough, but some control switches with flow displays need a power supply.