Flow Switches

What is a flow switch?

A flow switch is simply a device that monitors the flow of liquid, gas, or steam. When the flow reaches a certain pre-set flow rate, a switch is triggered that has the capability to signal an action, such as shutting down the flow entirely. This is done through electrical signals created by the switching mechanism. In principle, flow switches are similar to a light switch. They just happen to be in a stream of flow and do not require that a person be physically present to turn them off and on.

Flow switches can handle a wide variety of different media running through them, but by far, the most common media for flow switches are water and air.

What is a flow switch?

What is the difference between a flow meter and a flow switch?

Flow switches can either be simple stand-alone units that do nothing but monitor flow rates and trigger at a specified flow rate, or they can also be found as an integral element of a flow meter. Flow meters provide a continuous measurement of the flow rate and can also provide other functions essential to certain applications through integral electronics, like batching and totalizing.

Not all flow meters offer switching capacity, but it is important to note that for certain application areas, a flow meter with a switch may be the best choice because the flow meter can offer certain advantages for application specifications. For example, a simple flow switch may not offer high enough temperature specifications, but there may be a flow meter with an integral switch that can handle the high temperature.

Because flow meters are generally more expensive than simple flow switches, it is usually best to investigate stand alone flow switches first to see if there is one that can meet your application specifications. If there is not, then a flow meter that offers an integral switch may be the answer.

Flow switch vs flow meter

What is the difference between a flow switch and a pressure switch?

A flow switch monitors the flow rate of the media moving through a process line and a pressure switch monitors the pressure within a process line or pipe or vessel. Both pressure switches and flow switches essentially perform the same function, acting as a trigger for a function. They just monitoring different elements of an application. Pressure switches are used in many common places, like the air compressor you may have in your garage. They are also commonly used in pneumatics and hydraulics where force to move something is created by pressurizing a liquid or a gas.

Flow switch vs pressure switch

Types of Flow Switches

Flow switches are primarily classified by the media that they are monitoring (like air or water) the principle of operation, their installation method, and particular application areas. Many flow switches are versatile in that they can meet the needs of many applications. Below are some explanations of different types of flow switches.

Each type of flow switch will offer different advantages and drawbacks. Avoid costly errors down the road by making sure you have chosen the right flow switch for the job. Make use of our free expertise and let us do the work of choosing the right flow switch for your application and your budget.

Water Flow Switches

Water flow switches are plentiful and used in many different places. Most switches that are built for liquids can be used as water flow switches. KOBOLD offers a wide variety of water flow switches, including all metal versions for high pressures, low flow water switches, and plastic flow switches. We offer both inline and insertion water flow switches. Our available technology types for water include variable area, thermal, and paddle flow switches.

Water Flow Switch

Air Flow Switches

Air flow switches monitor the flow of air and most any flow switch marketed for gases is compatible with air. Our air flow switches are available in variable area, thermal, and paddle technologies. There are also inline and insertion models to choose from. It is worth noting that some flow switches like our KSR/SVN and S-Series are capable of monitoring both water and air. This is not true across the board as many switches are only able to monitor water or air.

Here are our suggested air flow switches:

Air Flow Switch

Inline Flow Switches

Inline flow switches are installed by placing them via integral connections into a piping system. They have a “flow body” where the mechanism of monitoring is located, and this is placed between two sections of pipe. Inline flow switches require that the installation either be a new piping system or if not, then the system must be shut down, the pipes must be cut, and the switch then installed. Existing processes requiring a new flow switch are sometimes easier served by an insertion style flow switch.

Here are our suggested inline flow switches:

Inline Flow Switch

Insertion Flow Switches

Insertion flow switches offer ease of maintenance and replacement over an inline flow switch. Generally, the switch electronics will be in a housing that remains affixed outside the pipe, while the paddle or measurement probe is placed within the flow path inside the pipe.

Here are our suggested insertion flow switches:

Insertion Flow Switch

Paddle Flow Switches

Paddle flow switches come in models for liquid (water) and models for gas (air). They are not as likely to be able to monitor both liquids and gases with one model. The monitoring mechanism is simple. A paddle is affixed via a hinge onto the housing where the electronical components reside. The paddle is placed into the flow stream and the force of the flow pushes the paddle downstream. The faster the flow, the more force is created and the more the paddle is pushed. The switch engages when the flow reaches a predetermined rate. Most paddle flow switches are insertion type, although there are inline models as well like our PSR.

Here are our suggested Paddle Flow Switches:

Thermal Dispersion (Calorimetric) Flow Switches

Thermal dispersion flow switches and calorimetric flow switches are different terms for the same technology. A heated probe is inserted into the pipe or duct via a hole in the piping and the housing while the electronics are always outside of the pipe. The flow of the liquid (water) or gas (air) passing by the heated probe dissipates the heat, much like when you stand outside without a coat and the wind removes your body heat and chills you. The temperature drop is then converted by the electronics and used to create a switch-point value. Visit our article on Thermal Flow Technology to learn more about this principle of measurement.

Thermal dispersion flow switches offer an advantage over variable area flow switches and paddle switches because there are not mechanical parts that experience wear and tear, so they require less maintenance and offer a longer service life than their counterpart technologies. Our KAL-Series thermal dispersion switches are best sellers and well known in the industry. They are in use around the globe in a variety of applications. They are available for both liquids and gas. They are also available in 3A models for sanitary applications.

Here are our suggested Thermal Dispersion Flow Switches:

Variable Area Flow Switches

Variable area flow switches operate on a simple principle. They consist of a glass or plastic or metal tube that contains a float inside it. The flow of the media moves the float as the flow increases. When the float reaches the pre-set limit, the switch is triggered.

Here are our suggested Variable Area Flow Switches:

Duct Flow Switches for HVAC

For monitoring the flow of air through HVAC Ducts, paddle flow switches are a good choice. They are used to control air flow set-points. When choosing a flow switch for your HVAC application, it is important to choose one with a dust-tight switch. Choosing one with an easily adjustable switch point that can be modified in the field is also advantageous. Our LSP model offers all these advantages.

Our suggested Duct Flow Switch for HVAC:

Boiler Flow Switches

Boiler flow switches can be used in different parts of the total boiler system. Because boiler water in certain parts of the process can be extremely hot, not just any flow switch will work. What is required is a flow switch with high temperature capacity, such as the flow switching capability included in our BGN All-Metal Variable Area Flow Meter. The BGN also offers the advantage of displaying the flow rate on an integral mechanical pointer scale. For incoming water feeds that are not hot, most any liquid (water) flow switch will be sufficient for monitoring the flow.

Flow Switches for Fire Systems

Flow switches for fire system management require accuracy and dependability. Most flow switches for fire systems are simple paddle switches. The flow switch monitors the flow of water through the pipe of the sprinkling system and there can be multiple switches in different parts of the line system. The switches are used to trigger an alarm when they reach a certain flow rate.

They are typically insertion mount flow switches where the paddle mechanism is fitted into the flow through a hole while the housing with the electronics remains affixed outside the pipe. Inline versions, like our PSR Paddle Flow Switches, are also an option if you prefer to install the device with an integral flow body directly into the piping.

When installing a paddle flow switch for a fire system, use a top mount installation for horizontal pipes and a vertical installation for vertical pipes where the flow is from the bottom up. Take care that the flow switches are kept far enough away from any places where the flow may change directions and keep them a significant distance away from and drains or valves. Be mindful of where they are installed so they can be easily accessed for service or replacement.

Make sure that the switch you choose can fit properly in the diameter of your piping. The length of the paddle cannot exceed your diameter and it should have a decent amount of clearance underneath the paddle so that the flow stream freely moves the paddle backwards to initiate the switch. It should not be hindered by the bottom of the pipe.

Here is our suggested flow switch for fire systems:

Water Flow Switches in Chillers

Industrial process chillers use different types of media in the cooling process, the most common being water or air. Water chillers are much more efficient than air models because the ability of water to dissipate heat is much greater than that of water. Chillers are used in a wide variety of industrial application areas such as automotive, food, beverage, semi-conductors, lasers, and machinery.

Water chillers use water or a water/glycol mix in a set of piping systems that is pumped to a process where it absorbs the heat produced by the process. This heated water is then returned to the chiller unit where it is cooled by the chiller through refrigerant and an evaporative process. The cooled water is then recirculated back to the process in a continuous cooling loop through the chiller and the process producing the heat. In areas where water availability is an issue, these systems limit the use of water by reusing it. Proper functioning of the chilling system is essential to protect valuable equipment from damage and to avoid any downtime from system failure.

Flow switches are used in the cooling circuit to verify flow and are an essential part of the process. Seeing as the cooling media is usually water or a water/glycol mix, many water flow switches are compatible, and the best selection depends on the exact application specifications. KOBOLD has partnered with many companies to provide rugged, dependable, and long-lasting water flow switches for chillers. The most popular models we sell for chiller applications are our inline variable area flow switches.

Flow Switches for Pumps

Flow switches for pumps are used in a piping system that contains liquid flow as part of a process. When the flow rate falls above or below the acceptable flow rate for the process, then the flow switch is actuated and triggers an electronic impulse that can either start or start a pump to increase or decrease line pressure. Turning the pump on increases the line pressure which increases the flow rate. When the pump is turned off, pressure is decreased, and the flow is slowed down. In tandem with pumps, flow switches are the guardians of the acceptable flow range for the process.

Flow switches for pumps also provide the extra benefit of extending the life of the pump and protecting it from damage. If the liquid flow ceases and it not detected, then the pump will run dry, which is damaging and should be avoided through a flow switch verifying that there is always flow to the pump.

Flow switches for pumps are used in a wide variety of applications including cooling tower systems, water and wastewater treatment, and many general industrial processes.

Choosing the right flow switch for your pump depends on the application parameters. The switch must accommodate the pipe size, the maximum media temperature, and the pressure in the line. It also must be able to tolerate the maximum and minimum flow rates of the process. Many flow switch technology types are acceptable for pump applications, and you can reference our flow product line here.

One example of our many suitable options is:

Low Flow Switches

Flow switches come with all different types of flow rate capabilities. Not all flow monitoring technologies can monitor or measure low flow rates. Low flow switches are flow switches that can sense the flow, even when it is very, very low. Depending on how low your flow rate is, certain standard flow switches may offer a low enough minimum flow rate. Our notable lowest flow capacity flow switches come in variable area technology.

Our lowest volume flow switches:

Flow Switch Selection: How do I choose?

Choosing a flow switch can be quick and painless if you speak to one of our expert engineers.

If you prefer to make the selection without any assistance, here are the application variables you should consider in flow switch selection:

Flow Switch Installation

Many flow switches, usually thermal and paddle type switches, are installed using an insertion method where a hole is created in the pipe and a connection is created/added to the hole that is compatible with the connection type on the switch. The paddle of the paddle flow switch or the thermal probe of the thermal dispersion switch are then inserted into the pipe to where they are in the stream of the flow. The housing with the electronics generally sits affixed to the outside the pipeline. We offer one paddle flow switch that already comes mounted in a section of pipe that is then connected to an incoming and an outgoing pipe, the PSR Paddle Flow Switch.

Because of the inherent monitoring/measuring principle, most variable area flow switches will be inline flow switches. These are installed as described above where the switch is part of a device that is inserted into the piping with a line coming in and a line going out that are affixed via connections on the pipes and connections on either side of the flow switch body.

Depending on the technology type of the flow switch, and to ensure accuracy, it is best to make sure that the flow is not turbulent around the flow switch and that it is kept as laminar as possible, without surges of flow. The way to protect against this is to make sure there is a length of “straight pipe run” before and after the flow switch where there are no bends, devices, or other elements that will agitate the flow. Visit our article to learn more about straight pipe runs.

Variable Area Flow Switch Installation

Other types of flow technology, such as a thermal flow switch with a digital display will require following the user manual to properly commission the device once it has been inserted and installed in the pipeline.

Flow Switch Maintenance

For any variable area float switches that are measuring media with contaminants, lime or dirt deposits on the housing and the internal parts should be removed regularly. To clean a variable area flow switch, proceed in the following manner:

If thermal or paddle flow switches experience build-up on their probes or paddles, they will also need to be removed and cleaned.

How do you test a flow switch?

Testing a flow switch is typically done by introducing flow into the system and then seeing if it triggers at the preset switch points. If you are not sure that it is switching at the correct flow rate, you can verify the flow rates easily if you are using a flow switch that is integral to a flow meter that will show you the exact flow rate at any given time. You can adjust the flow rate to the desired switch points and make sure the electrical output signals at those values.

Testing a standalone flow switch that is not connected to a flow meter can be a little less straightforward if you want to check the exact switch points. You can verify that it is switching though increasing and decreasing the flow to see if it is triggered or not. Flow could also be verified through another flow meter near the switch or through a rented clamp-on flow meter that shows continuous flow rate. But most switching applications aren’t going to require that degree of accuracy if the application did not require a flow meter in the first place. What is desired is a repeatable switching point.

If it does not seem that the flow switch is working, you can also test to verify that the electrical components are still functioning and that the switch has the power it needs to function.

How do you reset a flow switch?

Resetting a flow switch depends on the application that the flow switch is being used in. For example, in residential hot tubs, sometimes resetting the integral flow switch is as easy as turning the power off and on. For our purposes however, we are speaking about resetting a flow switch in an industrial process setting.

To reset or adjust the switch point of an industrial flow switch, consult your product manual as the method will vary based on both the technology type and whether or not it has a digital display/controller. Some variable area flow switches are as easy as sliding the switch contact mounted on the outside of the flow tube up or down to the desired flow rate on the scale printed on the flow body. Others, like a digital thermal switch, will likely require following the integral menu programming in the device.

How do I know if my flow switch is bad?

If your flow switch is no longer triggering at your specified flow rate or it is not switching at all, even though it is clear that the set flow rate has been reached, then the switch is probably bad. The first thing to verify is that the switch has power. If that can be confirmed, it may be time to repair or replace your switch. For paddle switches, you can also manually verify that the paddle is still correctly attached to the housing and is still moving freely.

Flow Switch Prices

Flow switches can vary in price depending mostly on the technology type and materials. For example, a metal flow switch will cost more than a plastic flow switch. Flow switches with digital menus and no moving measurement parts, like thermal dispersion switches, will also generally cost more. Switches that come as an integral part on a full flow meter that also provides continuous rate measurement and not just monitoring, will generally cost more.

But in general, flow switches are not very costly. To learn more about the prices of our flow switches, visit our flow switch products or speak with one of our engineers to find your ideal solution.

Flow Switch Manufacturers

While there are many flow switch manufacturers to choose from, KOBOLD offers one of the largest lines of industrial instrumentation in the industry. Because we have so many options, we are not in the position of other companies with limited product lines who may try to force one of their products for an application when it is not the right solution or the right price.

We are well versed in providing ideal application solutions for a wide variety of flow switching and flow measurement needs. Many of our flow switches are made here and assembled by hand in our facility in Pittsburgh. They are tested and verified before being shipped, providing peace of mind that the unit will function as intended straight out of the box.

If you are interested in learning more about why you should partner with KOBOLD for your application, please visit our "Why Choose KOBOLD" page.

Choose A Flow Switch Help
Featured Products
KAL-K
Thermal Flow Switch with Flow Trend Indication
KAL-K - Thermal Flow Switch with LED Flow Trend Indication for Water-Based Liquids

Made in the USA | For Water-based Liquids | Drift Stabilization | No Moving Parts | Negligible Pressure Loss | Up to 1,450 PSI and 250 °F | NPT and Tri-Clamp Fittings

LSP
Air Flow Switch For HVAC Ducts
LSP - Air Flow Switch for HVAC Ducts

For Horizontal Square/Rectangular HVAC Ducts | Adjustable Switch-point | SPDT Mechanical Switch | Up to 1,575 FPM and 85 PSI |

PPS
Plastic Paddle Flow Switch
PPS - Plastic Paddle Flow Switch

Made in the USA | For Liquids | Low Cost | Bi-directional | Low Pressure Drop | 9.5 to 28.5 GPM Switching Range | Up to 145 PSI and 225 °F

PSR - PS
Paddle Flow Switch
PSR/PS - Paddle Flow Switch

Made in USA | Low Cost | For Liquids | Adjustable Switch-point | Simple, Reliable Design | Brass or SS | Inline or Insertion | Up to 3,600 PSI and 230 °F

SMN
All Metal Flow Switch
SMN - Flow Switch for Liquids

Made in the USA | For Liquids | Low Switch Point Capabilities | Low Pressure Drop with High Flow Rates | Brass or SS | Up to 5,000 PSI and 212 °F

About KOBOLD

KOBOLD USA is a subsidiary of KOBOLD Messring GmbH, a world-leading instrumentation engineering business founded in Germany in 1980 by Klaus J. Kobold. With patented technology and superior service, the company quickly established itself as one of the global leaders in sensor and control systems with high quality products. The KOBOLD brand name became synonymous with superior quality and technological advancement in instrumentation engineering.

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